Amplifier design: Truths or Myths?

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Roger A. Modjeski

Re: Amplifier design: Truths or Myths?
« Reply #60 on: 21 Aug 2008, 02:05 am »
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.

pubul57

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Re: Amplifier design: Truths or Myths?
« Reply #61 on: 21 Aug 2008, 02:15 am »
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.

jeffreybehr

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Re: Amplifier design: Truths or Myths?
« Reply #62 on: 21 Aug 2008, 02:33 am »

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.)

pbrstreetgang

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Re: Amplifier design: Truths or Myths?
« Reply #63 on: 21 Aug 2008, 02:52 am »
Quote
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

JerryM

Re: Amplifier design: Truths or Myths?
« Reply #64 on: 21 Aug 2008, 04:04 am »
Quote
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

hmen

Re: Amplifier design: Truths or Myths?
« Reply #65 on: 21 Aug 2008, 04:47 am »
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.
       

6BQ5

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Re: Amplifier design: Truths or Myths?
« Reply #66 on: 21 Aug 2008, 05:45 am »

Power supply regulation in a preamp ....type and design ... does this have a big impact on the quality of sound?

mfsoa

Re: Amplifier design: Truths or Myths?
« Reply #67 on: 21 Aug 2008, 12:51 pm »
Quote
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

Roger A. Modjeski

Re: Amplifier design: Truths or Myths?
« Reply #68 on: 21 Aug 2008, 06:04 pm »

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.

« Last Edit: 22 Aug 2008, 05:15 am by Roger A. Modjeski »

AmpDesigner333

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Re: Amplifier design: Truths or Myths?
« Reply #69 on: 21 Aug 2008, 11:22 pm »
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...

6BQ5

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Re: Amplifier design: Truths or Myths?
« Reply #70 on: 23 Aug 2008, 01:59 am »
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.


Roger A. Modjeski

Re: Amplifier design: Truths or Myths?
« Reply #71 on: 23 Aug 2008, 04:01 am »
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?

6BQ5

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Re: Amplifier design: Truths or Myths?
« Reply #72 on: 23 Aug 2008, 04:28 am »
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



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




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.



AmpDesigner333

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REAL ADVICE ABOUT PICKING AUDIO POWER AMPLIFIERS
« Reply #73 on: 23 Aug 2008, 06:13 am »
Quote
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...

6BQ5

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Re: REAL ADVICE ABOUT PICKING AUDIO POWER AMPLIFIERS
« Reply #74 on: 23 Aug 2008, 07:02 am »

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.









AmpDesigner333

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Re: REAL ADVICE ABOUT PICKING AUDIO POWER AMPLIFIERS
« Reply #75 on: 23 Aug 2008, 07:31 am »

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.

6BQ5

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Re: Amplifier design: Truths or Myths?
« Reply #76 on: 23 Aug 2008, 02:38 pm »
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?



bummrush

Re: Amplifier design: Truths or Myths?
« Reply #77 on: 23 Aug 2008, 03:36 pm »
Class D is certainly not doing favors to audio.

art

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Re: Amplifier design: Truths or Myths?
« Reply #78 on: 23 Aug 2008, 04:09 pm »
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

AmpDesigner333

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Re: Amplifier design: Truths or Myths?
« Reply #79 on: 23 Aug 2008, 04:12 pm »
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...