AudioCircle
Other Stuff => Archived Manufacturer Circles => Music Reference => Topic started by: 6BQ5 on 28 Jul 2008, 12:54 am
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The story goes that audio-legend Paul Klipsch wore a button under his lapel that said Bullsxxt. He would flash it to someone who would engage with him on some audio-related topic (when appropriate of course).
I'm not at all an engineer, but like to read and learn to educate myself the gear I use and how they work (Roger's product manuals are great that way).
Over the years, I've come across various statements frequently made on discussion boards regarding amplifier design. As with all things, there is a bit of truth and some B.S. with each in the list below. These are NOT my ideas. Curious as to what others think ...
1. Transformers: The bigger “iron”, the better, hence massive power supplies and output transfers sound best.
2. Rectification: Tube rectification is better than diode, preferably with a choke in PS
3. Tubes: NOS is generally better than today's Chinese, Russian, Czech and former Yugo production. It's more than just testing well.
4. Parts I - Caps : Good ol’ Sprague caps sound better than new expensive exotics
5. Parts II - Materials: Silver is better if you can afford it. Silver transformers, wiring, etc…
6. Design: Fewer stages the better
7. Negative Feedback: Preferably none. Zero NFB is best
8. Design II: Class A … nuff said, generally sounds better than AB, B and other variants
9. Construction: Hand wired is generally better than PCB
10. Straight wire with gain : Tone controls are generally bad, another complexity to degrade the signal from "purity"
11. Transformer II: Transformer-coupled amps perform better than those using a cap between stages
12. Made in the USA: The Chinese don't care about quality of products. Made in the USA is best if you want your amp to last.
I would say with all of these, its a matter of implementation, thus "generalized" statements are mostly untrue. However, what is the "real story" with these? They can't be entirely right or wrong either.
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Hmm...FWIW, I'll add my 2 cents worth.
3. Few current-production tubes sound even acceptable, much less good or better. Of course there are exceptions.
4. Modern caps, especially the better film caps, do indeed sound better...quicker, cleaner, less edgy...than the old ones.
6, 7, and 8. I agree, as my favorite-sounding amps are SETs, by definition class-A amps, and those that sound best to me have no NFB.
As I said, FWIW. :?
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When I read the original post I wish I had one of those BS badges now :lol:
I don't particularly agree with any of the 12 points.
Everything must be taken in context.
I saw your disclaimer 6BQ5 so I know you are writing what you have read.
Now you need to learn to separate the wheat from the chaff.
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Audio is a religion full of dogma. With big money and big pride involved people try to get a leg up by inventing myths to hook consumers who navigate the waters using only "common sense." When believed, myths become reality. Audio technology is more subtle than common sense can comprehend but understanding isn't as much fun as believing, so suckers fall for the easy explanations then defend the myths and their pride. Developing an understanding of the technology will go a long way toward protecting you from the trappings of audio dogma, as will listening and experimenting for yourself.
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Audio is a religion full of dogma.
No argument there. Ditto.
Developing an understanding of the technology will go a long way toward protecting you from the trappings of audio dogma, as will listening and experimenting for yourself.
That's the hard part, and why I started this thread!!! :scratch:
I don't have the expertise, time and money to be testing transformers, caps, NOS tubes to come to my own conclusions. Thus I rely on other people's knowledge to help guide me.
There are people out there who make a living designing amplifiers, who are indeed, in a much better position to shed light on what is myth and reality, fact from fiction.
It just seems few people are willing to stick their neck out to set the record straight.
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It just seems few people are willing to stick their neck out to set the record straight.
IF you are actually concerned about those knowledgable in amplifier design sticking their knees out, why would you place this topic in a particular manufacturer's Circle? :scratch: This topic would be better served in a neutral Circle such as Audio Central where toes can't be stepped on and varied opinions can be openly shared. 8)
Cheers,
Robin
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Maybe he posted here because he was hoping Roger, as a well respected, no-nonsense designer would answer...
Bryan
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Given I own and RM-10 MKII and RM-5 MK III, certainly Roger's expertise would carry a lot if weitht.
But, other opinions are certainly welcome. :D
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Maybe he posted here because he was hoping Roger, as a well respected, no-nonsense designer would answer...
Bryan
Well that kinda goes w/o saying Brian. :lol: But when he specifically asked by so few folks were willing to stick their necks out, it suggested he was looking for more than just Roger's thoughts. I just thought he might get more responses in an open Circle,,, just like a variety of responses are generated from acoustic issues in the Acoustic Circle. Sound logical to you? :D
Cheers.
Robin
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But, other opinions are certainly welcome. :D
Maybe so,,, maybe not. Are you welcoming other amp designers to freely post their design ideas & philosophies here? I don't know about that, do you? :D
Cheers,
Robin
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Maybe he posted here because he was hoping Roger, as a well respected, no-nonsense designer would answer...
Bryan
Well that kinda goes w/o saying Brian. :lol: But when he specifically asked by so few folks were willing to stick their necks out, it suggested he was looking for more than just Marks thoughts. I just thought he might get more responses in an open Circle,,, just like a variety of responses are generated from acoustic issues in the Acoustic Circle. Sound logical to you? :D
Cheers.
Robin
Understand Robin. Thought maybe he was looking to Roger specifically due to owning the equipment. I'll agree that if he want's open discussion and everyone's opinion, the other circles would be a better place.
Bryan
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I can think of examples that will counter each of the first 11 numbered items. There are no absolutes in amplifier designs, just optimized designs based upon the designer's goals. There are also no "new" circuits in tube amps and preamps, but the quality of passive parts has steadily improved. Some current production tubes, not all or even most, are as good as the NOS from the 50s and 60s.
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As with all things, there is a bit of truth and some B.S. with each in the list below.
AND
I would say with all of these, its a matter of implementation, thus "generalized" statements are mostly untrue.
I'd say the above about sums it up.
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Maybe so,,, maybe not. Are you welcoming other amp designers to freely post their design ideas & philosophies here? I don't know about that, do you? :D
I'm surprised that posting here has caused so much confusion. Given I use Music Reference gear and I respect Roger's opinions, I felt this was a good place to start for me.
It's also a free world (last I checked), so I'm all ears to hearing other opinions and ideas.
If I'm causing problems, I can also just shut-up I guess.
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Maybe so,,, maybe not. Are you welcoming other amp designers to freely post their design ideas & philosophies here? I don't know about that, do you? :D
I'm surprised that posting here has caused so much confusion. Given I use Music Rerence gear and I respect Roger's opinions, I felt this was a good place to start for me.
It's also a free world (last I checked), so I'm all ears to hearing others opinions and ideas.
It wasn't my desire to cause you confusion, it was my desire to give you workable options so that you might just get your "educated" opinions from more variety of respectable amp designers . I'm sorry you can't follow that logic. :thumb:
Cheers,
Robin
ps, I'll just add that you ask very good questions and I for one would like to hear from designers from many different types of amplifier designs on their thoughts, not just from 1 manufacturer and a bunch of opinionated audiophiles. But I'm afraid that's all that will result from your thread emplacement,,, that is if Roger will offer his thoughts to your questions. :D
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I would say with all of these, its a matter of implementation, thus "generalized" statements are mostly untrue. However, what is the "real story" with these? They can't be entirely right or wrong either.
True! ... :D
You've answered you're own questions and other than that, there's far too much in there for any one post to answer in detail.
Take 12, on Chinese products though, just to look at one that others might not. I've used various Chinese products and the quality has been quite exceptional in all respects. Of more interest to me anyway, is the very different philosophical approach to design that can be seen in ideas like modular construction but that's a topic that could take up a page on its own. Also interesting, is the Chinese approach to intellectual property rights ... :), which can lead to all sorts of interesting copies of great designs. I'm sure there's Chinese junk out there as well.
jules
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Who the hell is Mark? :scratch: :wink:
Bryan
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Who the hell is Mark? :scratch: :wink:
Bryan
Another good question,,,,, now please answer my PM! :lol:
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6BQ5, I think Robin has a good point. Why not move this great post over to Audio Central and get a wider audience? You could PM Roger,...and Mark(?), asking for his feedback on the topic.
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6bq5,
Although they are not forbidden by rules to post anywhere outside of their own circle as long as their product or service (tricky interpretation here) is not mentioned, I believe most feel that it's not courteous to post in other industry circles without a direct invitation from the circle owner. So you would have more chance of getting someone from the industry to comment if this were in neutral circles like the Audio Central or Industry Talk. IMHO, good topic.
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Items 1-12 are all true and Items 1-12 are all false. :thumb:
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One reason it would be good to hear from Roger is that I think he has a bit Paul Klipsch in him, but stepping on toes in public isn't always fun. Another myth[?]: Good active preamps are better than passive preamps (assuming some proper matching between source and amp). If this myth[?] prooves false there sure is a lot of money at stake for owners and manufacturers. Secondary, related myth: Transformer-based passive are better than resistor-based passives.
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Well, how's about a few more myths and truths (to fall on deaf ears)? :oops:
What are we up to ... 25 now?
1. Transformer step-ups for MC stages are better than an active gain stage in a preamp
2. Massive power supplies with huge filtering caps are needed to get the most of an amp
3. A stepped resistor pot is best, preferably using Vishay type resistors
4. Some tubes sound "better" in a preamp than others, such as Telefunkens with little diamonds
5. Amplifier feet have a big influence on the quality of sound
6. Hybrid amps using MOSFETs sound warm and fuzzy
7. Tube amps have no bass, especially SET designs
8. SE amps have a purer midrange than PP types
9. Amps with metal fabrication (cases) have a hard sound because they are prone to RFI and EMI
10. Handwound transformers sound better than machine made transformers
11. High-current amps sound best
12. High voltage amps sound best
I can go on. No wonder the typical audio consumer is cynical with this kind of stuff floating around in the ether.
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I am shocked that you havn't mentioned that......opamps are the devils' children.
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I am shocked that you havn't mentioned that......opamps are the devils' children.
13. Op-amps are full of negative feedback and are the devils' children (even OPA627s biased into Class A).
13A. Op-amps have no place in high-end audio gear, a good designer should be able to design an optimized discrete circuit, which will always sound better.
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The biasing, internal or external, of an op-amp has nothing to do with the class of operation. And, if an op-amp did not have NFB implemented in or around it, it would be totally unstable. It would operate more like a comparator.
A well designed discrete circuit topology will usually outperform op-amp based topologies. Usually, not always.
One of the biggest myths I ever heard was; "I have a well designed amplifier but, I need a boutique power cord for it to sound its best".
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One reason it would be good to hear from Roger is that I think he has a bit Paul Klipsch in him, but stepping on toes in public isn't always fun. Another myth[?]: Good active preamps are better than passive preamps (assuming some proper matching between source and amp). If this myth[?] prooves false there sure is a lot of money at stake for owners and manufacturers. Secondary, related myth: Transformer-based passive are better than resistor-based passives.
Paul,
I would enjoy hearing your experience with the RM-9 SE, now that you have been listeneing to it for several months--particularly since you were a long term user of the CAT JL-2.
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GMuffley, I came to the RM9SE because I was looking for something that ran cooler than the CATJL2, which was a room heater in the summer. I started with the RM10MKII and loved it, but felt I needed a little bit more power so I tried an RM9MKII and the added drive was an improvement for my speakers, though I think the RM10 may be all you need with speakers 92db and up. I went to listen to an RM9SE in Virginia and fell in love with. I certainly had no complaints with the sound of the CAT, very powerful, dynamic, and transparent, but I find the RM9SE gives me every bit of that (perhaps a touch smoother), especially with a passive preamp, though it certainly works very well with the Joule LA150MKII I owned when I first got it. To my ears, the amp improved when I moved from the NOS Siemens EL34s to the KT88 RAM tubes, more dynamic, better bass, and larger sense of the soundstage. I take it is ultra reliable like all of Roger's designs (the CAT had no fuses to protect the resistors from tube failure, ugh.), and with the additional power and low impedance drive of the SE versus standard, can drive just about any speaker. My only hesitation was making a move from Class A to A/B and triode to ultralinear, the myths again. I strongly recommend the amp, but I think Roger only made 16 or so and maybe he has a handful left. I also had him add a ponytail extension for use with my own power cords, another myth I find hard to let go of.
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The biasing, internal or external, of an op-amp has nothing to do with the class of operation.
Interesting. I often see DIY people saying they bias an op-amp into Class A mode.
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Thanks to 6BQ5 for stating this thread and those who have participated. Going by the number of replies in a just a few days I see this is a hot topic.
Before I answer his 12 points I would like to share a recent experience in modding two RM-4 head amps that had been extensively modified previously. In one of them all 8 rectifier diodes were replaced with high speed diodes. If high speed diodes make a difference that is where to put them. Yet, on the other RM-4 the 8 original rectifiers were still in place and 3 other diodes were replaced instead. This mod replaced 3 diodes that are never "on" in normal use. They are there to protect the high voltage power supply from damage no matter what a technician does when he is poking around measuring voltages. I think we can safely say that replacing rectifiers that are never on in normal use cannot change the sound. Does anyone care to argue this point?
I have found the following:
1. Smaller output transformers have less iron to magnetize and less copper to go around a smaller core: thus lower magnetizing loss and lower copper losses. Music Reference output transformers generally have half the loss compared to others. It is interesting to note that the amount of iron determines the low end of the frequency response and the amount of copper and the way it is wound determines the high frequency response.
2. Tube rectification has certainly attracted a lot of attention along with the additional belief that a premium tube rectifier sounds better than a common one. A high power amplifier like an RM-9 or RM-200 would need 4 rectifier tubes as the power drawn from the supply is quite high at 500 mA per channel x 2 is 1 amp. Tube rectifiers cannot work into first filter caps larger than 40 uF. The first filter in most of my amps is 500 uF or more. Tubes work best with choke input filters but these supplies have very poor regulation and are not suitable for high power class AB amps.
3. Such a general statement is not likely to be true and how old does a NOS tube have to be to be NOS? More than anything, tubes vary from batch to batch just like cookies do. I unintentionally provide QC for several tube producers by letting them know when I get a batch that is not like the usual from that factory. The last time this happened I had bought some tubes and not tested them for a year. When I got around to testing them I found they had low gain and more noise than the usual from this factory. They sent me another batch made 3 months later. These were no better. They complained to the factory and a new sample was made for approval. This time the tubes were right again. These same tubes are used by other tube amp makers who apparently hadn't noticed the change in performance.
stay tuned for the next 3
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I would like to share a recent experience ...
:D
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I'll take that as agreement.
:D
I was liking the discussion you were having amongst yourselves. Please continue. I'll chime in now and then.
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I'll take that as agreement.
:D
I was liking the discussion you were having amongst yourselves. Please continue. I'll chime in now and then.
We're waiting for your 4, 5, and 6.
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Point :wink: Counterpoint :icon_twisted:
1. Transformers
The HK Citation II lovers seem to attribute a lot to "iron"
http://www.quadesl.com/refurb/refurb_hkCitation2.html
http://db.audioasylum.com/cgi/m.mpl?forum=vintage&n=161589&highlight=citation+Iron&r=&session=
2. Tube Rectification
Supposedly quieter than diodes, but do have their own drawbacks so it seems
Air tight tube preamp description http://www.katli.com/preamplifiers.htm
Both sides of the story ... http://www.welbornelabs.com/drd.htm
3. NOS
Tons of examples ... but this one is typical.
http://www.tonequest.com/articles/article3.htm
Maybe there is more money to be made selling NOS?
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Don't know enough about 1 and 2 to reply...still learning :D
However, I do have an opinion about NOS versus current production tubes. Do NOS tubes sound better? Many, I'm sure, do. But most, I'm sure, do not. Add to that the counterfeiting, the cross-labeling, the extortionate pricing, questionable testing and the lack of significant guarantees and I find that the risks involved with buying NOS aren't worth the 10X to 30X price difference. If after six months my $13 tube dies I won't sweat it. But if my $150 NOS tube fizzles in that time I'm going to be ticked. Current production still sounds way better than solid state to me.
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Don't know enough about 1 and 2 to reply...still learning :D
However, I do have an opinion about NOS versus current production tubes. Do NOS tubes sound better? Many, I'm sure, do. But most, I'm sure, do not. Add to that the counterfeiting, the cross-labeling, the extortionate pricing, questionable testing and the lack of significant guarantees and I find that the risks involved with buying NOS aren't worth the 10X to 30X price difference. . Current production still sounds way better than solid state to me.
Well the good one sound much better in most circuits. Reports that the superbly engineered MR and VAC gear fly against that statement but in the vast majority they for sure are better. If you buy NOS tubes you pay the premium from the good vendors or you become familiar with construction, date codes and vintages. If not you will be burned.
"If after six months my $13 tube dies I won't sweat it. But if my $150 NOS tube fizzles in that time I'm going to be ticked" Thats the beauty I find they last much longer in most cases :thumb:
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Re: NOS
I'm leery of tubes that have not been matched (if needed) or tested/graded for quality. I notice that some sites selling NOS tubes make no mention of the quality of the tube.
An example of good practice would be Upscale Audio, where Keven Deal categorizes every NOS tube, as to standard, low-noise and super low-noise quality.
Some tubes are just plain expensive because they have become rare as stocks have been depleted. So its basic supply and demand, and paying a huge premium simply based on scarcity rather than quality seems ridiculous to me. I once paid a premium for a pair of cryo'd Sylvania 6SNGT's which were nothing special if not noisy, whereas a cheap Mazda 6SNGT for 1/10 the cost sounded incredibly better. I learned my lesson, you don't always get what you pay for.
If I were a gear manufacturer, I just can't see being able to rely on NOS tubes, where a steady and reliable supply is important to meet production requirements. RAM cherry-picking new production is good practice, but I have seen postings here and there by people who have done some rolling that they have preferred NOS in quite a few cases over RAM tubes. I also question why RAM needs to be doing this in the first place ... policing the quality of tube manufacturers. Name me one other industry that does this ... I can't imagine a BMW dealership saying we pick out the best Beemers off the production line and only sell those. The QA in places like China and Russia must be then terrible if RAM is having to do this.
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Re: NOS
I'm leery of tubes that have not been matched (if needed) or tested/graded for quality. I notice that some sites selling NOS tubes make no mention of the quality of the tube.
An example of good practice would be Upscale Audio, where Keven Deal categorizes every NOS tube, as to standard, low-noise and super low-noise quality.
Some tubes are just plain expensive because they have become rare as stocks have been depleted. So its basic supply and demand, and paying a huge premium simply based on scarcity rather than quality seems ridiculous to me. I once paid a premium for a pair of cryo'd Sylvania 6SNGT's which were nothing special if not noisy, whereas a cheap Mazda 6SNGT for 1/10 the cost sounded incredibly better. I learned my lesson, you don't always get what you pay for.
If I were a gear manufacturer, I just can't see being able to rely on NOS tubes, where a steady and reliable supply is important to meet production requirements. RAM cherry-picking new production is good practice, but I have seen postings here and there by people who have done some rolling that they have preferred NOS in quite a few cases over RAM tubes. I also question why RAM needs to be doing this in the first place ... policing the quality of tube manufacturers. Name me one other industry that does this ... I can't imagine a BMW dealership saying we pick out the best Beemers off the production line and only sell those. The QA in places like China and Russia must be then terrible if RAM is having to do this.
Your right a manufacturer cannot rely on NOS tubes. It just isnt possible, Quicksilver did that once and now owners have to convert at great cost and different sound. Mr. Modjeski is a superb engineer and quite possibly has no time or patience for nothing but super tight matches in his tubes. That is not saying however that the same tight matched NOS tubes wouldnt sound better, or just sidestepping different in any case. If there was huge supply and sane prices of all NOS tubes, I wonder which ones he would prefer? I bet it would be a NOS of some vintage.
Also there is huge variance in cars and BMWs, I know Im in the industry of aftermarket performance tuning. There are few "ringers" with higher HP/TQ, and turbos that are just a bit more efficient. There are cars that are quite a bit more knock prone and put out less power than the norm too. You just would never know unless it is tested and compared to many other like vehicles under controlled conditions. (Like Roger does with tubes). Of course BMW doesnt say anything and doesnt consider it a problem. They are more picky and higher QC with the M cars that are mass produced then undergo hands on evaluation by BMW. Also special spec cars and cup racers are tightly matched- though they dont often stay matched because of a huge variety of reasons.
This is evident in the Mazda star series were everything is matched to a "T" though some specd racers put out 5% or more power after just a few laps. Complicated machines made by man are bound to be different even when they are the same.
It would be interesting to test long term validity of the special matching from RAM by testing a quad of KT88s when new, in 6 months then 18 months to see what variability is over the long term
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re: Rectifiers
It seems to me, that the main motivation for going back to tube rectification is to avoid some of the downsides with SS diodes, specifically the noise they can generate. However, tube rectification has its downsides too. Michael Elliott formerly of Counterpoint, when designing his new Aria preamp examined the tube rectification option and created a prototype.
(http://ariaaudio.com/WVImages/WV%20Proto%20Power%20Supply.jpg)
In the end, he said naw, and went with a conventional SS rectified power supply. Looking at that pic, can you blame him?
When I look at my RM-5, I see IN4007 diodes. These are run-of-the-mill diodes that go for as little as 3c bought in bulk.
The newest generation of Cree Schottky rectifiers (silicon carbide) introduced in the past couple of years, supposedly don't have the noise problems of standard diodes like an IN4007.
Would a Schottky in lieu result in audible improvement?
Wish I knew. Certainly, they are way more expensive, going for several dollars each.
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Any word on using SS regulator with tube rectification? I picked up a pre using this and it is impressive, It has replaced some decent classic pres and even went to personal preference against a stereophile class A pre
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RAM cherry-picking new production is good practice, but I have seen postings here and there by people who have done some rolling that they have preferred NOS in quite a few cases over RAM tubes.
You can find 'some people' who prefer anything old over new and who are willing to post their subjective opinions freely without too much trouble. Without the value of a blind test there's nothing more being reported than one man's opinion.
And if you want to talk about the shameless willingness to over charge then Kevin Deal is a good name to start with and Michael Elliot is a good one to finish with.
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I'm sure that is happening (people having pre-disposition or a bias towards NOS).
But I also see people who have the pockets to try out many different kinds of tubes (including) RAM, and have no other objective than describing their experiences, positive and/or negative, with RAM tubes, new production and NOS.
One thing I've seen said before on various boards: just because a tube tests well does not mean necessarily that it sounds good/better. Fact or fiction, I don't know, but I've seen that comment often enough to think that perhaps RAM tubes may test very well, but may not necessarily sound better than some of the NOS varieties fetching premium prices. RAM SLN tubes are not all that cheap either for that matter.
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Im not getting what you are saying. RAM tubes are just a test procedure and guarantee. RAM doesnt make tubes, the ones RAM offers are Chinese, EH, Sovteks, ect just like everyone else, except picked for tight tolerances. The rest not so great testing ones prolly go to the other New production tube vendors. You dont see any comments on a "better" sound of the RAM tubes. They dont sound better by themselves they sound like Chinese, EH, or other russian tubes because thats what they are. The tangible difference and the universal acclaim of RAM tubes are measured by the users love for the MR amps. Thats the whole point and its put into full effect by its utilization in the circuit Roger masterminds. Im sure RM doesnt use 1% resistors that measure 1.5% and Im sure he tries to get matched mirror channels in his amps- this is were the RAM tubes come in completing the integrity and the actualization of the circuit he is designing.
FWIW a clue that RM does recognize the sound difference in tubes is evident by the suggestion the Shugang KT88s on the tube page are an UPGRADE to the RM200 stockers.
Also you wont ever mistake a superb testing RAM EH6922 as sounding like a 50s or 60s Amperex. I cant imagine a person favoring the 6922- but I guess Ive seen crazier things
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...people who have the pockets to try out many different kinds of tubes (including) RAM, and have no other objective than describing their experiences, positive and/or negative, with RAM tubes, new production and NOS.
But their opinion is still totally subjective.
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Im not getting what you are saying.
Sorry for the confusion. I think we are saying the same thing.
Also you wont ever mistake a superb testing RAM EH6922 as sounding like a 50s or 60s Amperex. I cant imagine a person favoring the 6922- but I guess Ive seen crazier things
But this statement confuses me. Are you saying someone would favour the Amperex or RAM?
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But their opinion is still totally subjective.
I guess, such it is. Though I would argue, this is not necessarily bad or wrong if done without self-interest or a bias.
I remember Vacuum Tube Valley magazine once published a rating of various classic tubes such as 6L6GCs and 12AX7s (I think authored by Eric Barbour). Do you take issue with this too?
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Also you wont ever mistake a superb testing RAM EH6922 as sounding like a 50s or 60s Amperex. I cant imagine a person favoring the 6922- but I guess Ive seen crazier things
But this statement confuses me. Are you saying someone would favour the Amperex or RAM?
Yes 10 out of 10 times.
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I guess, such it is. Though I would argue, this is not necessarily bad or wrong if done without self-interest or a bias.
I remember Vacuum Tube Valley magazine once published a rating of various classic tubes such as 6L6GCs and 12AX7s (I think authored by Eric Barbour). Do you take issue with this too?
Yes, I would take issue because it's a limited perspective and highly subjective opinion.
I currently own a Threshold SS amp, Music Reference RM-9 and RM-10, Quicksilver monos, a Dynaco and Pathos and Counterpoint hybrids.
As an example rolling EL-34s in the Quicksilvers versus the RM-9 would lead to vastly different opinions about the same tubes. Both are respected, great sounding amps, but very different in the degree to which a tube has influence on the sound. The same 6922s rolled in both the Pathos and Counterpoint reveals a much greater influence of the tube on one of the amps as compared to the other. Which amp would you like me to base my opinion about either tube on ?
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Great points, and I agree.
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... reveals a much greater influence of the tube on one of the amps as compared to the other. Which amp would you like me to base my opinion about either tube on ?
So let's see if I understand ... Are you saying that a 6922 that sounds good in one amp will not necessarily sound better in another amp relative to perhaps another 6922? And if so, then opinions of tubes will vary amp by amp?
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I have come across some pres especially that all but negate the tubes in their circuit. Meaning they hardly sound like a tube pre in any sense, I think this is what he is meaning.
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I'm saying that the level of influence a tube has in the sound varies significantly by the amps design and an overall opinion about the tubes sound is highly subjective as a result.
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OK. I see. Thanks, I think I now understand.
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I am flattered to hear that Kevin has taken up my nomenclature for noise levels. Does he give numbers and limits or just his perception?
Price of NOS tubes appears to be a function not only rarity but of what is "the kind to have". Five years ago it was all about Telefunken and I couldn't find any enthusiasm for Mullard and Bugle Boys. Now it seems Telefunken has taken the back seat and the others have moved up front. Right now a fellow who specializes in supplying tubes to guitar players is cleaning me out of my Tungsram 12AX7s because they are the current favorite though a few years ago no one cared.
I scan eBay now and then and recently I was amused to see that Amperex PQ were bringing big bucks. Too bad I threw so many away when I was developing the Beveridge RM-1, they were unreliable, prone to developing noise in short order and very discouraging all in all.
You are correct, no sane manufacturer is going to fool with NOS. Though I have steady supply of current production tubes there are distinct differences batch to batch from the same maker. Factories are forced to substitute materials from time to time and hope nobody notices. The tubes may even be in spec but I pick it up right away because the testing I do is different and in addition to theirs.
The theoretical noise for the 12AX7 design is less than 1 uV making their average value about 5 dB above theoretical and their max almost 20 db above theoretical. My limits for the SLN are within 2 dB of theoretical (that is you can't find a 12AX7 that is better than 2db quieter. My LN is within 3 dB of the SLN and SG within 6 db of the LN.
Yes, I do the cherry picking for you. In a flat of 100 tubes there might be 5 that are Super Low Noise, there might be none as is the case with the Sylvania/JAN 6DJ8s that go for very little money. Other than being noisy they are great tubes, but you can't use them in any input stage. I went through enough to convince me that any low noise examples would be a miracle. Sylvania made good tubes but made them to perform well for their intended purpose which for the 6DJ8, was the tuner in a color TV. They are fine at high frequencies but have a lot of low (audio band) noise which did not effect the TV tuner. In a way, we are lucky that there are any low noise 6DJ8s.
This is why I developed a computer driven rack to gather and print the data for each section of each tube. Of course everyone has some "computer driven tube tester" but not for noise. I wouldn't even have attempted it had I not the experience of chasing down noise in the RM-1 preamp and RM-4 headamp where the noise referred to the grid is less than 0.3 uV. To give you some perspective on that I like to use money because we all understand and appreciate money in our everyday lives. Since we are going down to the small change we have to start big. So let's have a volt be 1 million dollars. Your CD player has a typical output of 2 volts so that's $ 2 million. That means a microvolt is $1 and thus my grid noise is 30 cents. Which is a very small amount compared to the $2 million output of the CD player. In the world of vinyl a moving magnet cartridge is typically 5 mV so its voltage output is $ 5,000 while a moving coil will be 0.5 mV or $500. The RM-4 employs 2 sections of a 6DJ8 which reduces the noise by 3 dB thus reducing the grid noise to 0.21 uV or 21 cents, 9 cents better than a single section and very small compared to the $500 output voltage of the MC cartridge. If you like sums more than fractions just ask yourself how much difference is there between $5,000 and $5,000.21? Hardly any, but I have to work pretty hard to get the noise down to 21 cents out of $5,000.
At first I tested these tubes one at a time. The RM-4 was selling well and I had to have tubes for them.
Listening for noise and judging their quietness is not something you can easily teach someone nor will your senses be uniform from day to day. How about the ambient noise? So here is a case where measurements really do make sense and my philosophy is if you are going to charge someone $60 for a SLN tube you ought to measure that tube's noise and if you can measure it let the user have the measurements.
Who would want to go through 100 tubes to find the 5 best and what to do with the rest, but that's my problem, not yours. There are maybe 20 that are LN and there is very little demand for the Standard Grade although I am happy to advise where these tubes will perform flawlessly and contribute less than 0.1 0dB additional noise to the overall circuit. In any two stage amplifier or single stage with a cathode follower only the first tube need be low noise. The second will have to be quite noisy to make any noticeable contribution to the total.
There are only a few tubes that actually have ever had a noise spec. Noise testing is very difficult and not part of a factory's test procedure, I know because I visited the factories and asked them. At EI, the most syphosticated equipment was a Tektronix curve tracer that hadn't worked for several years. I asked them how they produced the curves for the KT-90. The chief engineer said, "we did it steady state with meters, and we did it fast" They had to do it very fast or the tube would go up in flames. This is not the way to generate curves.
What makes noise testing difficult is separating the tube noise from the noise of the tester. White noise from a tube doesn't look any different from white noise from the input of the tester. These are very small voltages going into very high gain amplifiers. The gain of my tester is about 100,000 times which is 100 dB. The gain when I listen via a speaker to check things out is 120 dB. At that gain I can hear everything and I can verify that the numbers printed on the label indeed represent the performance of the tube. Besides the microphonics I can hear the cathode expanding and pushing itself through the mica in little bursts. I can also hear the noise come up as the tube comes on and go down as the tube's transconductance goes up and steadies out in about 15 seconds. Even though there is not much change from there on, some tubes take a good half hour to show some particular problems so they get to soak an hour before the computer runs the test. I get very very few returns, less than 1%.
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Historically there have been fewer than a dozen tube types that have a noise spec at all. A good example is the 12AX7/7025. In many cases the manufacturer simply got the 7025s from the 12AX7 run picking out enough to get what they expected to use for the year. These got branded 7025 and sometimes 12AX7/7025 which is called a "double brand". For that tube the spec is rather lose at 1.8 UV average and 7 UV (microvolts referred to the grid) maximum. In the same manual, the average noise spec is the same 1.8 uV with no stated maximum. Noise is always "referred to the grid" as that takes the gain of the tube into account. Thus all the manufacturers be it RCA, GE, Sylvania or anybody had the same published spec and the same retail price to the penny. Consulting a 1983 price list the 12AX7/7025/ECC83 is a triple brand, it's one tube, no difference at all. By this time either the noise spec was being ignored or all the tubes met the max limit. Of course they weren't testing all the tubes, usually they would test a few out of every thousand. Most tubes were made only once a year in one batch that was determined by past annual sales. If RCA ran out of 12AX7's before the the next run they would simply buy them from their friendly USA competitor or from Europe. The run for a popular tube like the 12AX7 would typically be several hundred thousand. Fender alone was buying 100,000 a year.
They all used the same specs, gave the same applications and were proud of things they had learned. At one point Sylvania was buying plate material for rectifiers from RCA because it had lower back current than their plate material. Those were the days of standardization by the Radio Electronics Television Manufacturers' Association (RETMA). See http://en.wiped.org/wiki/RETMA_tube_designation for more information.
Many current production tubes are not within those specs and there is no official organization to police them. Some of those variations are purposely designed to be different, principally for the guitar amp industry. I have been told many times "For every one tube we sell for a Hi Fi amplifier we sell 100 to the guitar players". We are indeed a small segment of now small market. Although I am not the "Tube Policeman" I do work closely with several importers, letting them know when things have gotten out of hand at the plant. I also get pre-production samples of new designs for evaluation. There are at least 8 distinctly different 12AX7s in current production and they will sound different among their applications. The sonic range of these variants is greater than the range of NOS tubes.
None of this is meant to discourage those willing to take the time to experiment with different tubes, both NOS and current production. There are no "standard" operating parameters (plate, grid or cathode voltages and currents) and many preamps have some parameter which can be very sensitive to either gain, plate voltage or plate current. In a feedback RIAA phono preamp I have measured 2 dB frequency response changes due to gain (mu) alone. That will be quite audible by making the bottom end rise, fall or stay flat in the lower octaves. How one hears this and expresses what he hears with words is an individual thing. We do our best to describe what we hear with language that is drawn from other arts. If a Telefunken tube has more bass than some other brand it may be that their average gain is higher or lower than the standard. But this is a tube/amplifier interaction and not attributable to the tube alone or expected sound in some other amplifier.
When I was developing the RM-9 I realized that the popular output tubes could all be used in the same amplifier if I made the bias range large enough, the filament supply strong enough and the amp stable enough to handle the range of transconductance in popular output tubes. In addition I added a 3 position switch to allow an increse or decrease of about 6dB from the nominal value. For those who are not familiar with the Manley-Modjeski letters in Stereophile around 1985, David took issue with my granting freedom to compare these different tubes in the same amplifier. He contended that things like plate load impedance, operating voltages etc. were written in stone in the tube manuals and must be adhered to the letter. One might think that a 6550 has only the few applications listed in the data book when, in fact, there are an infinite number of possible applications. The purpose of these applications is to give the engineer some guide lines of what sort of voltages, currents and load impedances will give reasonable results. The applications usually cover a range that includes single ended, push pull class A, AB1, AB2, and class B configurations which for some tubes range from a few watts to 100 watts per pair. New tubes, like the 8417 and the 7591 were designed to be particularly attractive to new designs. In the 8417 the transconductance is twice the average of most power tubes thus allowing lower bias voltages and lower drive requirements. It allowed the amp design to have one less driver tube. Rather penny wise and pound foolish. In my opinion they went to far with this idea the result being a rather unstable, squirrely tube. It found its way into only a handful of designs, most notibly PA amps where power and economy were paramount and fidelity was not important. None of the European tube companies bothered with making it and I believe Sylvania and GE were rather sad they ever released it. :(
So I made an amp that would properly run the major output tubes types. At the time I could find no other amplifier that would run EL-34s, the whole KT series (KT stands for Kinkless Tetrode), the 6L6/5881 series and the 6550. I didn't think is was reasonable to say a EL-34 was more musical and a KT-88 was more authoritative when the comparison had to be done in amplifiers of very different design. All the Marantz amps used EL-34's while Audio Research and CJ employed the 6550.
One final comment about tubes, numbers and sound. A 6922 is a 6DJ8 equivalent. They have the same specs. The 4 digit number system designates "industrial" tubes which were sometimes constructed with extra micas, some wire straps holding the elements in compression between the micas all of which was up to the particular maker of the tube. It was even permissible to put 6922 on all or part of a 6DJ8 production run with no internal differences and no extra tests. As tube production became smaller and smaller the tubes might carry both numbers on the tube and on the box. Therefore, a 6922 is not necessarily better than a 6DJ8, nor does it have any inherent sonic advantages.
For the 28 years I have been providing RAM tubes to tube enthusiasts around the world I have been rewarded for my efforts by many a customer for two things in particular. The quotes go something like this:
"I've had this preamp for 10 years, tried lots of tubes, noticed 'tube rush' and accepted as fact that tubes cannot be as quiet as solid state. Now with your tubes the noise is gone"
"Your tubes let me hear more detail and the silence between the notes"
When asked to comment on the subject of NOS verses current production I demur. On cryo treatments I chuckle and on the white gloves I say. "Skip the silly gloves, these are not quartz lamps, just wash the peanut butter off your hands first, that gets kinda messy." BTW, Who started this silly notion that you can't touch the glass?
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re: No fingers on the glass tubes?
I think I know that one. It also ages me.
Remember when .... you had the good old flash bulbs for use with cameras? Or, 1st generation halogen lights? Circa 1960s and even early '70s.
I remember studying photography back then in school, and that was the first thing you were taught: NEVER ever put your fingers on the glass bulbs. The reasons why ... well, supposedly the oils from fingers would remain on the bulbs, resulting in a hot spot when the flash would go off and the bulf could explode. Or with halogens, this would limit the life of the bulb or even cause them to explode too. They were much more delicate back then I guess.
Somehow, someway, the same logic wound up extending itself to vacuum tubes.
Roger, there are markings on my RM10 RAM EL84 tubes. Can you explain what those mean?
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Let me clairfy: Oil from fingers is not and never has been a problem for tubes. They are nothing like halogen bulbs new or old. As to flash bulbs, I have some of the old ones that are as large as a 100 watter but I have no desire to fire them off. The magnesium wool inside is quite attractive.
Tube mythology is a backwards thing when compared to Greek Mythology as it runs in the other direction getting more and more fantastic as time moves forward. Just chat with an old timer radio repairman or radio amateur and he will laugh at the things that are currently taken as fact today.
Due to the large numbers of tubes that have to be tested for a run of 100 amplifiers I wrote a program specifically to test RM-10 tubes at the actual operating voltages and currents. The number refers to the group to which that tube belongs. The groups are very tight with no more than 1/4 volt of grid bias difference in any group. We often ship replacement tubes by their groups if the amp is an RM-10.
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Roger,
you've touched on something here that I've long been wondering about:
There are only a few tubes that actually have ever had a noise spec. Noise testing is very difficult and not part of a factory's test procedure, I know because I visited the factories and asked them. At EI, the most syphosticated equipment was a Tektronix curve tracer that hadn't worked for several years. I asked them how they produced the curves for the KT-90. The chief engineer said, "we did it steady state with meters, and we did it fast" They had to do it very fast or the tube would go up in flames.
Using Telefunken as an example, there are common specs for the E88CC, 6922 and the CCa. On paper there is absolutely no differences in figures or tolerances between the E88CC and the CCa. Current mythology suggests that the CCa tube was selected on the basis of better measurements and low noise. The former belief appears to be wrong. The latter belief appears to be founded on a "low noise" standard that CCa tubes represented the best 10 or 15% [different figures from different sources]. The standard was apparently a requirement since the tubes were used for telephone services [a fine example of hi fi audio in the fifties :lol:] but my question is this:
a) am I right in thinking that "low noise" was the sole difference between a CCa and a 6922
and
b) can you shed any light on the actual testing procedure used for selecting low noise 6922/CCa tubes?
Thanks for the thoughts you've been sharing above. Knowledge of the thinking behind early tube design is something it would be sad to lose.
Why, for example, did manufacturers move away from D getters? Was it for economy or was it regarded as a design improvement.
Sorry, I'll stop now. This is supposed to be an amp design thread :nono:
What are the markings on your tubes 6BQ8?
jules
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[quote author=K.C.
You can find 'some people' who prefer anything old over new and who are willing to post their subjective opinions freely without too much trouble. Without the value of a blind test there's nothing more being reported than one man's opinion.
And if you want to talk about the shameless willingness to over charge then Kevin Deal is a good name to start with and Michael Elliot is a good one to finish with.
[/quote]
Yes I finished with M J Elliot many, many years ago.
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Roger, what do you think of this "myth" or "truth"?
HIFI-Tuning Fuses
By Robert Deutsch • September, 2007 Tweaks come and go. When a new one creates a buzz in audiophile circles, I generally prefer to wait and see if it's still around after the initial excitement has subsided. I'd heard about "audiophile" fuses some time ago, and although the likelihood of them making a significant difference didn't seem as farfetched as such tweaks as the "intelligent chip" or the "clever little clock," I didn't feel inclined to try them. I was persuaded otherwise by the confluence of two separate influences: a report by Michael Fremer, in the February 2007 Stereophile, that the HiFi-Tuning fuses produced a "subtle but noticeable" improvement in the sound of his Musical Fidelity kWP preamplifier; and an encounter at the 2007 Consumer Electronics Show with Robert Stein of importer Ultra Systems (the HiFi-Tuning fuses are made in Germany), who said that they produced a big improvement and offered to send me some samples.
When you think about it, the notion that a fuse can make a difference is not that implausible. If, as most designers of high-end audio electronics will admit, the kind of wire used for a component's internal wiring can make a difference, then why not a fuse? After all, the job of the fuse is to melt when a certain level of current is reached, so might there not be differences in how various fuses react to current at lower levels, possibly constricting or otherwise influencing the power used by the component? The HiFi-Tuning fuses use pure silver wiring, gold-over-silver endcaps, and ceramic rather than glass casings for better resonance characteristics. But a plausible mechanism of action and the use of high-quality materials are one thing; audible improvements are something else.
My first test involved the PS Audio GCC-100 integrated amp, a product I hold in very high regard; if its performance could be improved simply by replacing a fuse, that would be great. I talked to the PS Audio folks to find out what the GCC-100 uses in the way of a fuse, and was told that it uses two, both located on a circuit board, and that accessing them was a bit tricky. Before tackling the job, I unplugged the GCC-100's AC cord for a couple of hours to allow its capacitors to discharge, then removed the screws securing the chassis cover and gently lifted it a bit, looking for the wiring harness that would have to be unplugged before I could proceed. Once I'd located and unplugged the harness, replacing the fuses was pretty easy.
Before doing any of this, I spent some time listening to the GCC-100 to refresh my memory of what it sounds like. Yes, the tonal neutrality, resolution, transparency, and rhythmic thrust that had originally impressed me were still there. If the HiFi-Tuning fuses were to improve on this, they had their work cut out for them.
But improve the sound they did, and not just marginally. The PS Audio GCC-100 now sounded clearer, more dynamic, with improved transients—simply better all around. The difference was big enough that I didn't feel I had to go back and forth between fuses to convince myself that I was hearing it. But I did so anyway, if only to satisfy myself that what I was hearing was not the result of the mere act of replacing fuses, which to some degree can't help but serve to clean the contacts of fuse and fuse holder.
It wasn't. The improvement in sound was far out of proportion with the $60/pair cost of the HiFi-Tuning fuses. (Under its Critical Link label, PS Audio markets special fuses for its own products that are priced about the same as those from HiFi-Tuning. I briefly tried a pair of Critical Links in the GCC-100, and they, too, produced an improvement over the stock fuses.)
As I note in the main body of my Onkyo A-9555 review, the A-9555 benefited similarly from the use of the HiFi-Tuning fuses. As with every tweak, your mileage may vary, but the HiFi-Tuning fuses, available from www.ultrasystem.com, represent what I found to be a very worthwhile sonic improvement for a relatively small investment.—Robert Deutsch
Go Blow a Fuse, Michael Fremer, February 2007 (Vol.30 No.2):
When I was a poor audiophile, I loved tiny tweaks. Without switching out components, I could improve my system's sound without spending too much money. Bypassing or replacing cheap capacitors, cleaning connections, applying Star typewriter-cleaning gum to vibrating headshells, and other tiny tweaks made memorable sonic improvements.
I recently replaced the cheap fuses in my Musical Fidelity kWP preamplifier with fuses made by HiFi Tuning in Germany, sent to me by The Cable Company. These have silver filaments, ceramic bodies, and gold-over-silver terminations, and damn if they didn't seem to produce a subtle but noticeable improvement in smoothness and coherence. For less than $30 each (available in various sizes they're worth trying, if only for the diversionary entertainment.—Michael Fremer
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I hold Stereophile in high regard both in their listening tests and John Atkinson's (JA) measurements. As far as I know JA has not touched this subject and I would be surprised if he did.
As to fuses in general I use more than any other maker and I have studied them in dept. The RM-9 MK II has 11 of them. The RM-200 has 6. I am very careful how I apply and select fuses to not interfear with the amplifier's performance. The benefit for the owner is that they protect both the amplifier and tubes. The benefit for me is that I have very very few amplifiers to fix.
There is no reasonable argument that an inch of silver wire in a ceramic tube with gold plated end caps would affect the sound in the least. Of course it's presence can affect the listener who will want to hear a difference. It's a free country and anyone can make any claims about anything. Shame on the makers of such foolish things. I do my best to discourage my customers from throwing their money at something so futile.
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Agree about JA. For me, the best part of the equipment reviews in Stereophile are JA's comments in the measurements section, easy to read between the lines too. I did try the fuse thing, I could not hear a difference; but my ears are 50 years old. By the way, the KT88s your recommended are terrific in the RM9SE.
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Also you wont ever mistake a superb testing RAM EH6922 as sounding like a 50s or 60s Amperex. I cant imagine a person favoring the 6922- but I guess Ive seen crazier things
But this statement confuses me. Are you saying someone would favour the Amperex or RAM?
Yes 10 out of 10 times.
Really? Someone would favor the Ampererex or RAM tubes 10 out of 10 times? Fascinating.
(ahem...READ 6BQ5's question, pb.)
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Really? Someone would favor the Ampererex or RAM tubes 10 out of 10 times? Fascinating.
(ahem...READ 6BQ5's question, pb.)
You so right- enjoy your tubes
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Really? Someone would favor the Ampererex or RAM tubes 10 out of 10 times? Fascinating.
(ahem...READ 6BQ5's question, pb.)
You so right- enjoy your tubes
:rotflmao: :rotflmao:
Wicked sense of humor there, pbr :thumb: Thanks for the chuckle!
Jerry
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1. My main amplifiers, Atma-Shere M60's have no output transformers. i like them a a lot more than previous tube amps I've owned that have output transformers. I can see the importace of quality transformers although bigger doesn't always mean better.
2. I suppose it depends on the implementation but let's face it - there are some cool looking rectifier tubes.
3. From my experience, true in most cases.
6. Would seem to be common sense, but again it's in the implementation.
7. I have a switch on the back the my amps that provide 2 decibals of NFB. I can't tell the difference when I use them.
8. This is subjective and depends on the system. I prefer class A. FWIW, I think most people would usually agree that X WPC of class A sounds better than X WPC of class AB but obviously there are situations where only the most powerful (and expensive) class A amps can do the job.
11. I think the quality concerns about Chinese made audio are compounded by the fact that a lot of people who thought they got bargains ended up finding out they had no customer support.
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Power supply regulation in a preamp ....type and design ... does this have a big impact on the quality of sound?
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There is no reasonable argument that an inch of silver wire in a ceramic tube with gold plated end caps would affect the sound in the least. Of course it's presence can affect the listener who will want to hear a difference. It's a free country and anyone can make any claims about anything. Shame on the makers of such foolish things. I do my best to discourage my customers from throwing their money at something so futile.
But what did you hear when tried the upgraded fuses in your amps? Oh, that's right, you can tell what things sound like without hearing them. Pretty cool skill - It'd save us all a bunch of $$ if we could do that too.
Given the positive comments from professional reviewers and John Q Public I find it easier to believe that the fuses do indeed do something to the sound than to attribute this whole thing to mass hallucination.
-Mike
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Power supply regulation in a preamp ....type and design ... does this have a big impact on the quality of sound?
Power supply regulation is very important in the early gain stages of a system. When Peter Moncrief was testing several phono pre-preamps around 1980 he found many of them caused his woofer to move considerably every time the elevator in his apartment building was used. I recall he congratulated me on my voltage regulator in the RM-4 was unaffected by the voltage drop that was caused by the start-up of the elevator. The RM-4 and RM-5 regulators are solid state, with very low output impedance, low dropout and very tight line regulation. He also noted that the Counterpoint SA-2 headamp made his woofer move considerably in time with the elevator. That regulator had 3 tubes and a tube rectifier. The problem could have been poor line regulation or actual regulator drop-out which is caused when the line voltage drops below the minimum that the regulator can work with. A good number for drop-out is 100 Volts AC. This will cover most low voltage situations.
Regulation and dropout can be easily determined by raising and lowering the line voltage with a variac while observing a cone speaker or an oscilloscope. I had the opportunity to check the regulation (tube type) in a currently made preamp and found it to drop out at 115 VAC. Since it was a line only preamp there was not much output disturbance. Since 115 VAC is possible in many situations this preamp has a fair chance of being in and out of regulation which makes one question the value of the regulator at all.
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The story goes that audio-legend Paul Klipsch wore a button under his lapel that said Bullsxxt. He would flash it to someone who would engage with him on some audio-related topic (when appropriate of course).
I'm not at all an engineer, but like to read and learn to educate myself the gear I use and how they work (Roger's product manuals are great that way).
Over the years, I've come across various statements frequently made on discussion boards regarding amplifier design. As with all things, there is a bit of truth and some B.S. with each in the list below. These are NOT my ideas. Curious as to what others think ...
1. Transformers: The bigger “iron”, the better, hence massive power supplies and output transfers sound best.
2. Rectification: Tube rectification is better than diode, preferably with a choke in PS
3. Tubes: NOS is generally better than today's Chinese, Russian, Czech and former Yugo production. It's more than just testing well.
4. Parts I - Caps : Good ol’ Sprague caps sound better than new expensive exotics
5. Parts II - Materials: Silver is better if you can afford it. Silver transformers, wiring, etc…
6. Design: Fewer stages the better
7. Negative Feedback: Preferably none. Zero NFB is best
8. Design II: Class A … nuff said, generally sounds better than AB, B and other variants
9. Construction: Hand wired is generally better than PCB
10. Straight wire with gain : Tone controls are generally bad, another complexity to degrade the signal from "purity"
11. Transformer II: Transformer-coupled amps perform better than those using a cap between stages
12. Made in the USA: The Chinese don't care about quality of products. Made in the USA is best if you want your amp to last.
I would say with all of these, its a matter of implementation, thus "generalized" statements are mostly untrue. However, what is the "real story" with these? They can't be entirely right or wrong either.
Someone pointed me to your thread. I'm glad you started off with the Klipsch story. Here's a brief story for you... I grew up with audio. My Dad (now passed) had various hi-fi equipment all around the house, and even built custom equipment for family members (tape decks, speakers, receivers). I learned electronics, especially related to audio from a very early age. At 8 years old, I was able to take a cassette deck apart and put it back together. Coming full circle... My Dad always said "there's no such thing as magic". I live by this. We used to visit the local high end shop and audition speakers and equipment. My Dad rarely made a purchase due to cash limitations. Anyway, he used to tell me about all the myths and bullsh-t in high end audio. A good example is stuff like $10,000 speaker wires. I have to eat dinner now, so I'll cut this short and return to add more later...
Check my thread out:
http://www.audiocircle.com/index.php?topic=58526
Circles > Audio/Video > Industry Talk and Events > Topic: Digital Amplifier Company DAC4800A and Cherry amps
I try to take on the "BS" regarding amplifier design.
I'd like to address your list... More later...
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Power supply regulation is very important in the early gain stages of a system.
This "Lithos" regulator caught my eye, described as: "a discrete fast transient response time ultra low noise a devise 1000 times quieter, 53 times faster, and five decimal places more accurate than the best regulators available."
http://www.soundsofsilence.com/tom_evans.htm
In the end, I wonder how much of a perceptible difference such claims make.
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I went to the site and found very little information on the power supply. Could you send me a link to a specific page.
However, I particularly liked this part...
Like the Groove, The Vibe sounds very Tube like and has a sonic signature that is very difficult to pin down. Used with other source components, The Vibe offers the sonic equivalent of what the Hubble Space Telescope is to traditional optical astronomy; a far cleaner window into time and space.
His claims of the regulator are specious. It can't be done unless his reference is a very, very poor regulator. 1000 times quieter than my regulator would be .001 micro volts. It's very difficult if not impossible to make an AC voltmeter with less than 0.1 microvolts of self-noise over the audio range. The Sound Technology distortion analyzer is 5 uV at the input and my noise meter is 10 times better at 0.5 uV.
When solid state guys claim they have captured the sound of tubes I wonder why they are not using tubes. The reference to the Hubble is amusing in many ways. Will he have to send up the shuttle to fix things up like they did in the Hubble?
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Tom Evans actually sells a tube power amplifier, though this preamp is SS.
There is more information on his Lithos regulator and preamp design here.
http://6moons.com/audioreviews/tomevans2/vibe.html
(http://6moons.com/audioreviews/tomevans2/hero_lithos.jpg)
Quote:
"Tom claims that commercially available voltage regulators suffer voltage noise equivalent to the output of a moving coil cartridge. If you want to uncover all of the information contained in very small audio signals -- like those output by moving coil phono cartridges -- you want an audio signal with the minimal possible corruption and maximum possible dynamic range. This requires vanishingly low noise. If noise and signal are similar in magnitude, a significant amount of data is irretrievably lost. Off-the-shelf regulators also exhibit very slow transient response and recovery times, compounding the signal degradation begun with the noise issue. Tom decided that the only alternative was to develop his own high-performance high-speed regulators, which he christened Lithos. His first efforts at designing them yielded results that were a staggering 1000 times quieter, 53 times faster and 100,000 times more accurate than the best commercially available regulators used for audio applications at the time."
Here too, is another after-market regulator, though, no astounding claims made by Allen Wright.
http://www.vacuumstate.com/index.tpl?rubrik=13&lang=2
(http://www.vacuumstate.com/images_upload/gross/sreg_1.jpg)
Both of these caught my attention, because (in relation to the 10 truths and myths), its only recently that I've seen any emphasis on power supply regulation as having much of an effect on sound in a preamp or amplifier. For the longest time, power supplies seemed to be all about beefier power supply caps.
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There is no reasonable argument that an inch of silver wire in a ceramic tube with gold plated end caps would affect the sound in the least. Of course it's presence can affect the listener who will want to hear a difference. It's a free country and anyone can make any claims about anything. Shame on the makers of such foolish things. I do my best to discourage my customers from throwing their money at something so futile.
But what did you hear when tried the upgraded fuses in your amps? Oh, that's right, you can tell what things sound like without hearing them. Pretty cool skill - It'd save us all a bunch of $$ if we could do that too.
Given the positive comments from professional reviewers and John Q Public I find it easier to believe that the fuses do indeed do something to the sound than to attribute this whole thing to mass hallucination.
-Mike
Here we go... First, I'm always weary of reviews from magazines. There are hardly any bad ones in fear of "burning bridges", getting sued, or losing a potential advertising client. No magazine in their right mind will admit to this. In fact they will deny it tooth and nail. Same deal for "product rewards"; many are bought and paid for indirectly. Reviews that simply show measurements and no opinion whatsoever can usually be trusted, but are hard to find. Measurements can't tell you everything, but can tell you a lot. Manufacturers rarely falsify or embellish measurements due to fear of getting caught. However, there are some tricks that can make measurements look better, such as rating power at 10% THD, but this is also very rare. The most trustworthy source of how something sounds (beyond measurements) is actual customers. However, people have a tendency to like whatever they bought, so watch out for reviews that have no comparisons to anything else. Regarding well recognized brand names, don't believe that just because a brand is well known and has a long history that they only make spectacular products. I had a WELL KNOWN (maybe the MOST well known amp brand of all) amp and was explaining my total disappointment with it to a friend. He said something like "I can't believe you bought one, everybody knows that amp sucks. It sounds just awful and was a complete failure for them". He also said that despite the bad sound of this design, they sold a TON of them. One important figure is signal to noise ratio. Anything less than 100dB with respect to rated power should be avoided like the plague. There's no reason in this day and age that you can't design just about any type of amplifier at least that good. Noise is the enemy of good sound! If there is an SNR measurement at 1W, look for at least 85dB. This is A-weighted. Unweighted SNR is not as meaningful of a spec since the human ear has frequency dependent sensitivity curve. The "ear near the tweeter" test is actually quite useful if you have a single tweeter that's no more than 2" long in any direction. Listen not only to how much noise there is but also the character of the noise. Quality amps are dead quiet or close at idle. Look for amps with THD+N below 0.01% for a good portion of the power curve and at all frequencies. This is especially important at low levels, so look for THD+N well under 0.1% at 1KHz, 100mW. Unfortunately, many manufacturers don't provide this spec, and if they do, it's probably on a graph (THD+N versus power), not in text, and sometimes you need to interpolate. Look for amps with direct coupled output. Output transformers are fine for distributed audio in your local supermarket sound system. They saturate at low frequencies. Another one... Damping factor under 50 is a red flag. If damping factor or output impedance (reciprocal of this divided by the load impedance is damping factor) is not mentioned, it's probably poor. Also, as damping factor goes higher and higher it means less and less. I doubt any human being can hear the difference between an amp with a damping factor of 300 and one with a damping factor of 450 that's otherwise the same. Regarding the "sound" as perceived by any reviewer comparing two or more amps, if the comparisons aren't double blind, they aren't super valuable. The mind simply can't remove bias reliably otherwise. Single blind is much more meaningful than non-blind. You might also be surprised how many so-called "golden ears" fail double blind listening tests (essentially can't tell the difference) when the amps are similar! It's funny to hear the excuses when you call them on it. This is especially amusing with aftermarket modifications. My theory is "buy something that was designed right in the first place". Anyway... Regarding output power, watch out for manufacturers of anemic amplifiers that tell you their 30W amp is great for driving your 10-driver per channel tower speaker system. You need adequate power to drive your speakers through peaks unless you never "turn it up". Big speakers need big power to play loud and clean at the same time. I recommend a few hundred watts minimum per channel unless you're driving a pair of bookshelf speakers in a small room. Also watch for amps with lots of power but bad specs otherwise. Beware of amps with a spec called "instantaneous peak power" of something similar. This is technically twice RMS output power at rated output right before clipping. If you see this rating and it's NOT twice rated power, there's something fishy going on. This spec is used deceptively so beware of its use either way. Regarding inputs, when possible, insist on balanced inputs or both unbalanced and balanced. Balanced audio is inherently better due to built-in noise cancellation, and if you can afford a good preamp with balanced outputs, use one for your primary audio system. Here's something I wrote regarding pro amp measurements more than 3 years ago:
http://www.livesoundint.com/archives/2004/dec/power.pdf
Yes, I worked in pro sound for several years, but learned a lot. I know lots of high-end people think anything pro audio is junk. They are just wrong.
Second, unless you are an amplifier design engineer, chances are you will not be able to make heads or tails of what supposedly is best in circuit design. Good paper designs can also be implemented poorly in actual hardware. I hope to explain more in a another post soon, going through the list in the first post. In general, watch out for BS about amps that sound great but have poor specs. Having great specs is no guarantee of great sound, but if you care about accuracy, amps with bad specs are usually not going to deliver accuracy. Circuit details about the kind of rectifiers or output transformer or "special capacitors" might sound like real engineering talk, but much of the stuff I've seen like this is simply marketing and many times a bunch of crap. Here's one: If someone told you the black chassis sounds better than the silver one is obviously full of it!
Third, some people don't have good enough ears to tell the difference between amps and will swear up and down that their new 30W amp with really high THD and noise they just bought sounds better than the 200W amp with near perfect performance that they previously owned. An "audiophile" I used to know told me that the 48KHz bit rate internet radio he had sounded better than his CD collection! Would you trust his opinion on amplifiers? In my humble opinion, there are way too many lies out there about audio equipment in general. I find this insulting to consumers. Amplifier design is part science and part art. Good amplifier design is much more science than art. Great amplifier design is nearly 100% science. Here's hoping you see right through the hype... I wrote quite a bit, so please forgive any errors, especially spelling and grammar...
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Here we go... First ...
I'm kind of disappointed with your comments thus far, they are all over the place. Why not address the specific points in my first posting?
Many of your observations are also arguable too:
1. Minimum S/N Ratio <100db
2. Minimum amp THD+N of < .01%
3. Damping factor minimum of 50
4. Ideal amp power of 200W RMS
5. Transformers are detrimental and saturate (kind of hard to escape with tubes, unless you favour OTL, and even then) DC-coupled is better
I'd avoid the McIntosh forums, some of the engineers there will take you task regarding transformers (Mac is religious about the merits of their "autoformers" in their SS designs) and they argue that anything over 20 damping factor is superfluous. As for power ... well, there are quite a few people (myself included) where a 200W amp would be an overkill (I use Klipsch rated at 99/db/w/m) My RM-10 (only 30W) is fine. I also think the specs on my RM-10 are .3% THD, so obviously, it would not qualify as a hi-fi amp per your criteria, and I would argue otherwise.
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Here we go... First ...
I'm kind of disappointed with your comments thus far, they are all over the place. Why not address the specific points in my first posting?
Many of your observations are also arguable too:
1. Minimum S/N Ratio <100db
2. Minimum amp THD+N of < .01%
3. Damping factor minimum of 50
4. Ideal amp power of 200W RMS
5. Transformers are detrimental and saturate (kind of hard to escape with tubes, unless you favour OTL, and even then)
I want to address your list eventually, item by item. I even sent myself a reminder to do so. It's just VERY late here (after 3AM) and I should really be sleeping!!!
Sorry, but I'm not a big fan of tube amps in general, but OTL is definitely preferred. I was involved in a study once comparing good SS to popular tube amps, and similar informal blind listening tests since. I'm always surprised how many people prefer SS when they don't know what amp they are listening to. Tube lovers will argue this to death. Tube amps just don't have the "umph" of clean high power SS. What that means to you depends on your taste in music and speakers. Also, as an engineer (and perfectionist), I find tube designs to be old fashioned and plagued with pactical issues.
I like the sound of Class-D the best. Second place is Class-A. Don't get me wrong, I have heard some good sounding tube amps, but they are usually inefficient (heat), large, fragile, overly expensive, and unreliable. I don't like audio equipment because it glows or is "just retro cool". I believe in hard core engineering and technology to make things that work better. I'm pretty upset about what MP3s have done to audio, though! Thanks for reading.
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Well, some of what you say is true ... but not always the case with tube gear. Generalizing will lead to religious battles ... let's not go there ... however I must say that...
Roger Modjeski's designs at Music Reference aim to be:
1) Good value for the dollar
2) Environmentally friendly and efficient
3) Reliable ... both in the short and particularly over the long-term
4) Sound good
I think Roger has specifically focused on these areas because he's been around the block, and at one point in his career repaired many a tube amp of other brands and makes, and saw exactly the downsides that you say. He tends to be very no-nonsense, no baloney type of guy (engineer) and has a track record to prove it with some very desirable gear floating around as part of his legacy. He's well respected (the RM-200 is Stereophile Class A rated) in audio circles though his positions on things hi-fi related also has created detractors.
One of the reasons I've bought and use MR gear is because I like this no B.S. philosophy, and in particular, his willingness to speak openly about his design implementations and design objectives. Which is why his perspectives on some of the truths and myths I listed above I think are insightful to anyone interested in hi-fi.
I'd be curious as to your thoughts on the above list of 10 points?
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Class D is certainly not doing favors to audio.
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That is your opinion, and only an opinion.
I have designed and built virtually every style of SS amp that you can name (and maybe a few that you can't). All have their strengths and weaknesses.
As an engineer who actually does listen, I may conclude some of your opinions fall into the myth category.
But that is only my opinion.
Peace, man.
Pat
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Class D is certainly not doing favors to audio.
This will be a quick one (family stuff today), but I WILL get to the initial list soon...
Class-D is very difficult to design, and many manufacturers have done a bad job of it (lack of experience). I remember when CDs were rejected at first because they are "digital junk". When Class-D is done right, it can be very pleasing to the ear; combining the delicate textures of tubes at low levels and the heart pounding raw power of "big solid state".
More later...
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Send one to hi fi critic and see what they come up with
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I will start with a disclaimer: NB (note well) that I am not a digital amplifier designer, that I have only a passing interest in them and I have no opinion about how they sound. If any class D amp designer cares to state how he has solved any of the problems below I welcome his information. I also welcome any class D amp designer to state his noise specs, frequency response graph, output impedance from 20-20 kHz, short-circuit protection and level of emitted radiation at the switching frequency. Does anyone make on that will drive a 10 uF capacitor (big electrostat) at 20 Khz?
I was working on an unusual class D amp about 19 years ago with Mac Turner, a very intelligent EE. Power MOSFETs were just coming online. The Motorola first edition data book that I have is dated 1984 and is about 1/2 inch thick. By the time Mac and I were at it the IR book was about 2 inches thick and MOSFETS were cheap and easy to get.
The earliest commercial Hi Fi class D amplifier I know of was the Infinity SWAMP which I saw at CES in 1975 driving their SERVOSTATS. Kudos to them for trying and putting a lot of money at it but they were just too soon, the fast switching MOSFETs we have now were not available. They used the fastest switching transistors available but they were not nearly as fast as what we have now.
I know there are many terms for these amps and many designs floating around now; B&O, Tripath and others. I would not call these "digital amps" though I see that term used now and them. They are actually closer to analog amps until you get to the output stage and that's a BIG, FAST Switch. Keep in mind that the switching needs to be very fast just to get the amp to go to 20 KHZ. Fast switching also simplifies the output filter, which is the biggest, and not often mentioned, problem in these amps. Also note that these amps are not necessarily "faster" than other amps and often do not have even as wide bandwith as many tube amps notwithstanding their often derided output transformer.
Now here's a real bugaboo. Many of these amplifiers have feedback before one gets to the output filter thus the filter is out of the loop. What happens then is the amp becomes sensitive to load impedance and will either peak up if the load is higher impedance than the design load or roll off if it is lower. I do recall seeing a test of such an amp in Stereophile in the past few years and it did just that.
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Well, some of what you say is true ... but not always the case with tube gear. Generalizing will lead to religious battles ... let's not go there ... however I must say that...
Roger Modjeski's designs at Music Reference aim to be:
1) Good value for the dollar
2) Environmentally friendly and efficient
3) Reliable ... both in the short and particularly over the long-term
4) Sound good
I think Roger has specifically focused on these areas because he's been around the block, and at one point in his career repaired many a tube amp of other brands and makes, and saw exactly the downsides that you say. He tends to be very no-nonsense, no baloney type of guy (engineer) and has a track record to prove it with some very desirable gear floating around as part of his legacy. He's well respected (the RM-200 is Stereophile Class A rated) in audio circles though his positions on things hi-fi related also has created detractors.
One of the reasons I've bought and use MR gear is because I like this no B.S. philosophy, and in particular, his willingness to speak openly about his design implementations and design objectives. Which is why his perspectives on some of the truths and myths I listed above I think are insightful to anyone interested in hi-fi.
I'd be curious as to your thoughts on the above list of 10 points?
Thanks 6BQ5 for stating my design principles simply and accurately. The RM-10 that I brought out in the early 1990's was the first tube amp where I gave great attention to power consumption. The best measure I could come up with was: rated watts out/idle watts in. This is what is happening up to the point where you play the amp really loud (near clipping) where line power does go up but is dependent on program material. In most listening situations the line draw moves up less than 10% from the idle value. The RM-10 came in with a rating of 70watts RMS capability with 60 watts idle, a number a bit better than 1 (1.16). A Dynaco Stereo 35 which has the same output tubes draws 85 watts from the wall at idle making its green factor 35/83 = 0.4, very close to 3 times more line draw for half the output power. Now these are small numbers but I obtain similar numbers in the RM-200. Even the little EM7-5 does well for a class A single ended amplifier drawing about 40 watts for 10 watts of output. It plays efficient speakers loud enough for my taste and draws less than an RM-10 in absolute terms. We know there are lots of 8 watt (16 w. total) 300B amps out there that draw more than 50 watts and easily up to 100.
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Tom Evans actually sells a tube power amplifier, though this preamp is SS.
There is more information on his Lithos regulator and preamp design here.
http://6moons.com/audioreviews/tomevans2/vibe.html
(http://6moons.com/audioreviews/tomevans2/hero_lithos.jpg)
Quote:
"Tom claims that commercially available voltage regulators suffer voltage noise equivalent to the output of a moving coil cartridge. If you want to uncover all of the information contained in very small audio signals -- like those output by moving coil phono cartridges -- you want an audio signal with the minimal possible corruption and maximum possible dynamic range. This requires vanishingly low noise. If noise and signal are similar in magnitude, a significant amount of data is irretrievably lost. Off-the-shelf regulators also exhibit very slow transient response and recovery times, compounding the signal degradation begun with the noise issue. Tom decided that the only alternative was to develop his own high-performance high-speed regulators, which he christened Lithos. His first efforts at designing them yielded results that were a staggering 1000 times quieter, 53 times faster and 100,000 times more accurate than the best commercially available regulators used for audio applications at the time."
Here too, is another after-market regulator, though, no astounding claims made by Allen Wright.
http://www.vacuumstate.com/index.tpl?rubrik=13&lang=2
(http://www.vacuumstate.com/images_upload/gross/sreg_1.jpg)
Both of these caught my attention, because (in relation to the 10 truths and myths), its only recently that I've seen any emphasis on power supply regulation as having much of an effect on sound in a preamp or amplifier. For the longest time, power supplies seemed to be all about beefier power supply caps.
I took a good look at Tom Evan's website and found the following spec on his Linear A amplifier.
---LINEAR A SPECIFICATIONS---
Frequency Response: 12Hz to 90kHz-these are 0dB down points! Flat.
Power: 25.2wpc Class A
Output Noise: 150dB down 700microvolts(!)(not millivolts)
Output Impedance: 0.5 Ohm
Input Sensitivity: .7millivolts
Price: $8900
His noise output is not referenced so I'll give him the most generous spec. and compare it to his 25 watt output. The answer is 86 dB (20 log 14volts/.7 mv= 86 db), not 150 dB. This makes me doubt his power supply noise claims also.
The Frequency Response spec makes little sense "0 dB down" how about 1 or 3 like the rest of us do.
My output noise is typically 150-300 uV, yes microvolts, not millivolts.
The Input Sensitivity is likely .7 volts not millivolts.
Hey, I've had some errors in my specs too, none of us is perfect. I hope he will clean this up especially since he is claiming noise numbers that are not achieveable with active regulators unless you have a resistor feeding a big cap filter after them which both slows them down and degrades the output impedance.
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Tom Evans actually sells a tube power amplifier, though this preamp is SS.
There is more information on his Lithos regulator and preamp design here.
http://6moons.com/audioreviews/tomevans2/vibe.html
(http://6moons.com/audioreviews/tomevans2/hero_lithos.jpg)
Quote:
"Tom claims that commercially available voltage regulators suffer voltage noise equivalent to the output of a moving coil cartridge. If you want to uncover all of the information contained in very small audio signals -- like those output by moving coil phono cartridges -- you want an audio signal with the minimal possible corruption and maximum possible dynamic range. This requires vanishingly low noise. If noise and signal are similar in magnitude, a significant amount of data is irretrievably lost. Off-the-shelf regulators also exhibit very slow transient response and recovery times, compounding the signal degradation begun with the noise issue. Tom decided that the only alternative was to develop his own high-performance high-speed regulators, which he christened Lithos. His first efforts at designing them yielded results that were a staggering 1000 times quieter, 53 times faster and 100,000 times more accurate than the best commercially available regulators used for audio applications at the time."
Here too, is another after-market regulator, though, no astounding claims made by Allen Wright.
http://www.vacuumstate.com/index.tpl?rubrik=13&lang=2
(http://www.vacuumstate.com/images_upload/gross/sreg_1.jpg)
Both of these caught my attention, because (in relation to the 10 truths and myths), its only recently that I've seen any emphasis on power supply regulation as having much of an effect on sound in a preamp or amplifier. For the longest time, power supplies seemed to be all about beefier power supply caps.
I took a good look at Tom Evan's website and found the following spec on his Linear A amplifier.
---LINEAR A SPECIFICATIONS---
Frequency Response: 12Hz to 90kHz-these are 0dB down points! Flat.
Power: 25.2wpc Class A
Output Noise: 150dB down 700microvolts(!)(not millivolts)
Output Impedance: 0.5 Ohm
Input Sensitivity: .7millivolts
Price: $8900
His noise output is not referenced so I'll give him the most generous spec. and compare it to his 25 watt output. The answer is 86 dB (20 log 14volts/.7 mv= 86 db), not 150 dB. This makes me doubt his power supply noise claims also.
The Frequency Response spec makes little sense "0 dB down" how about 1 or 3 like the rest of us do.
My output noise is typically 150-300 uV, yes microvolts, not millivolts.
The Input Sensitivity is likely .7 volts not millivolts.
Hey, I've had some errors in my specs too, none of us is perfect. I hope he will clean this up especially since he is claiming noise numbers that are not achieveable with active regulators unless you have a resistor feeding a big cap filter after them which both slows them down and degrades the output impedance.
Roger,
First, let me say that it is an honor to be corresponding with you.
I posted some comments about tube amps in general here:
http://www.audiocircle.com/index.php?topic=58526.msg522734#msg522734
Also, let me comment that your designs are well beyonw typical from what I understand, and I wish to do an A/B comparison of my amps to the RM-200. I thought a neighbor of mine had these, but he doesn't (I asked today). He just bought a pair of Quad amps (KT-66?) and has several other tube amps that I have listened to very carefully. Thanks for your open discussion, and I do plan to go through the original list tonight.
Best Regards,
Tommy / DAC
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I will start with a disclaimer: NB (note well) that I am not a digital amplifier designer, that I have only a passing interest in them and I have no opinion about how they sound. If any class D amp designer cares to state how he has solved any of the problems below I welcome his information. I also welcome any class D amp designer to state his noise specs, frequency response graph, output impedance from 20-20 kHz, short-circuit protection and level of emitted radiation at the switching frequency. Does anyone make on that will drive a 10 uF capacitor (big electrostat) at 20 Khz?
I was working on an unusual class D amp about 19 years ago with Mac Turner, a very intelligent EE. Power MOSFETs were just coming online. The Motorola first edition data book that I have is dated 1984 and is about 1/2 inch thick. By the time Mac and I were at it the IR book was about 2 inches thick and MOSFETS were cheap and easy to get.
The earliest commercial Hi Fi class D amplifier I know of was the Infinity SWAMP which I saw at CES in 1975 driving their SERVOSTATS. Kudos to them for trying and putting a lot of money at it but they were just too soon, the fast switching MOSFETs we have now were not available. They used the fastest switching transistors available but they were not nearly as fast as what we have now.
I know there are many terms for these amps and many designs floating around now; B&O, Tripath and others. I would not call these "digital amps" though I see that term used now and them. They are actually closer to analog amps until you get to the output stage and that's a BIG, FAST Switch. Keep in mind that the switching needs to be very fast just to get the amp to go to 20 KHZ. Fast switching also simplifies the output filter, which is the biggest, and not often mentioned, problem in these amps. Also note that these amps are not necessarily "faster" than other amps and often do not have even as wide bandwith as many tube amps notwithstanding their often derided output transformer.
Now here's a real bugaboo. Many of these amplifiers have feedback before one gets to the output filter thus the filter is out of the loop. What happens then is the amp becomes sensitive to load impedance and will either peak up if the load is higher impedance than the design load or roll off if it is lower. I do recall seeing a test of such an amp in Stereophile in the past few years and it did just that.
Roger,
Sorry about the bad spelling in my last post. My laptop battery was about to go, and I wanted to post before I had to start over.
You are correct about the history here. Making a good digital amp was nearly impossible back in the 70s and 80s. I tried, though, with lack-luster results.
Regarding output filter designs, I could write a book on this. Wrapping feedback around the filter actually has some serious downside. I have designed amps like this and the compensation required (even using various modulation techniques) can defeat the purpose. If the output filter is designed just right, it is only affected by the load at ultrasonic frequencies. Even then, the difference is only a few dB from open circuit to 4 ohms. Take a look at the effect on output amplitude here (DAC4800A/Cherry):
http://www.digitalamp.com/DAC4800A%20standard%20measurements%20v3.pdf
http://www.digitalamp.com/cherry%20measurements%20v6.pdf
Several years ago, I went to the trouble of plotting the compound response of the output filter driving the actual speaker load for a few different speakers, and it came out very flat. Many speakers also have controlled impedance in the crossover that makes sure the natural rise in tweeter impedance is kept in check and doesn't do to open at ultrasonic frequencies. The problem I've seen is that many "digital amps" (Class-D, really) are not such good designs, and come from engineers with very little experience in the field. Going from analog amp design to digital amp design is not easy, and many manufacturers just wanted to get something to market to show that "they can do it too". I've been at it for 20 years, and this is the only reason I can be confident in my conclusions. However, the proof is in the pudding --- listening. Thanks again, and have a great day!
Warm Regards,
Tommy / DAC
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I hope he will clean this up especially since he is claiming noise numbers that are not achievable with active regulators unless you have a resistor feeding a big cap filter after them which both slows them down and degrades the output impedance.
Obviously something is amiss. I'm surprised no one else caught this type of error earlier.
Assuming these regulators were actually substantially "better" than typical PS regulation (whatever that may mean given the dubious specs) ... would this translate into a noticeable audible improvement?
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The story goes that audio-legend Paul Klipsch wore a button under his lapel that said Bullsxxt. He would flash it to someone who would engage with him on some audio-related topic (when appropriate of course).
I'm not at all an engineer, but like to read and learn to educate myself the gear I use and how they work (Roger's product manuals are great that way).
Over the years, I've come across various statements frequently made on discussion boards regarding amplifier design. As with all things, there is a bit of truth and some B.S. with each in the list below. These are NOT my ideas. Curious as to what others think ...
1. Transformers: The bigger “iron”, the better, hence massive power supplies and output transfers sound best.
2. Rectification: Tube rectification is better than diode, preferably with a choke in PS
3. Tubes: NOS is generally better than today's Chinese, Russian, Czech and former Yugo production. It's more than just testing well.
4. Parts I - Caps : Good ol’ Sprague caps sound better than new expensive exotics
5. Parts II - Materials: Silver is better if you can afford it. Silver transformers, wiring, etc…
6. Design: Fewer stages the better
7. Negative Feedback: Preferably none. Zero NFB is best
8. Design II: Class A … nuff said, generally sounds better than AB, B and other variants
9. Construction: Hand wired is generally better than PCB
10. Straight wire with gain : Tone controls are generally bad, another complexity to degrade the signal from "purity"
11. Transformer II: Transformer-coupled amps perform better than those using a cap between stages
12. Made in the USA: The Chinese don't care about quality of products. Made in the USA is best if you want your amp to last.
I would say with all of these, its a matter of implementation, thus "generalized" statements are mostly untrue. However, what is the "real story" with these? They can't be entirely right or wrong either.
I addressed each point on your list here:
http://www.audiocircle.com/index.php?topic=58526.msg522867#msg522867
This was put on my thread since I want my readers to see it. Hope you don't mind. Feel free to copy it back here. There are posts on that thread with a LOT more detail about the same topics, so please read through and comment. I'm a HUGE fan of good amp design, not just Class-D or Class-A or tubes. I'm NOT a fan of gimmicks, and feel they are an insult to audio enthusiasts!
Please note that these answers are no replacement for a long roundtable conversation! Thanks for your patience in addressing this list.
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Bad regulators can cause problems worse than simple R C power supply filtering. However, good regulators will give better results as they will have constant impedance over the audio band. In my studies of HV regulators in many popular preamps I was rather disappointed with their performance. In addition, most of them are not short-circuit proof which I find unforgivable.
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Many of the items discussed in this thread are covered in this excellent new article by Nelson Pass on the Six Moons website - in particular: negative feedback, amplifier classes, and distortion measurements. Very much worth a read and quite an education on amplification!
Nelson Pass http://www.sixmoons.com/industryfeatures/distortion/distortion.html (http://www.sixmoons.com/industryfeatures/distortion/distortion.html)