AudioCircle
Other Stuff => Archived Manufacturer Circles => Aspen Amplifiers => Topic started by: whubbard on 28 Apr 2008, 09:00 pm
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I'm going to be putting in a TKD stepped attenuator (with the Bob Crump Vishay S102 mods) into my GK-1m. The big problem is that Michael Percy doesn't have any more of the 25k (which hugh recommends). He only has 10k, 100k, and 250k. I went ahead and told him that 100k would be okay, as I figure higher is better than lower. Will there be any loss in sound detail because of the 100k, or will the GK-1 not really be able to tell much of a difference?
Hopefully someone will get back to me soon, as its a bit time sensative.
Thanks,
West
EDIT: I called Michael back up, and he was very helpful. I am going to be using S102s of 100k, instead of 250k, which he explained will bring the impedance down to around 50k, which seems like it will be fine, right? Especially considering the input on the GK is around 45k, and then my input on my ASP is probably going to be 47k (but im modding it so I can make it pretty much anything).
I was wondering however if anyone thinks putting this into a t-pad setup would have better sonics? If so, would someone mind pointing me into the right direction of doing this?...is it worth it?
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West,
Go LOWER, not 100K. I'd suggest 10K. The Zout of the SS section of the GK1 is very low, around 30R, so 10K will be fine. 25K is optimum, but 10K will be quieter than 100K.
With a 10Vpp signal, that's 5V peak, the current through a 10K pot is 5/10mA =0.5mA. The output stage of the SS section of the GK1 runs at 12.6mA, and 0.5mA is just 4% of this, which is fine as the margin reaches up to around 25%.
Sorry for my silence; I'm advancing as usual on four fronts.
Cheers,
Hugh
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Thanks Hugh.
I will go with the 10k, but still use the 100k vishays as I assume it will be pretty much the same as 250k vishays in this case.
How exactly would the sonics be different with a 20k attenuator? Lower noise floor? Noticable to a human?
-West
p.s. I totally understand you've been busy, so take your time. But when you get a chance, would you mind looking at my email from 4/20? Thanks Again.
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West, the resistors need to be 10 to 12 times the attenuator rating, so 100k S102's for the 10k TKD are fine.
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Would anyone care to elaborate for an electronic illiterate like me on what constitutes a good value for money stepped attenuator. For example, Theo has said a simple cheap as chips DIY Audio attenuator gave him a big improvement. Admittedly it uses reasonable/good Vishay Dale resistors and is of ladder type construction.
However, names like TDK, DACT and Goldpoint etc. seem to offer better potential quality but at a commensurately greater cost. Is a ‘cheapie’ worth it over the standard pot as it seems to me that Hugh has optimised the circuitry beautifully for a simple pot? Or should I save up for a far better implemented solution and is ladder really best V series or shunt in the case of a GK1?
:D
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I am certainly no expert, but here was my thinking.
I could have gotten a Shallco attenuator from Michael for $130 with all the PRP/Holco resistors. It would have been an improvement from the supplied pot. However, I would rather spend $250 (+$100 for the Vishays) and do it once, instead of getting the update bug later on. It the same way that I'm going to be putting in Sonicap Platinums. There are caps in the middle that would make a difference, but I would rather do it once, and do it right. I would assume that the difference form the supplied pot to the Shallco would be bigger than the difference from the Shallco to the TKD, but again, I wan't to do it once, and do it right.
The other fact is that the TKD + Vishays was Bob Crumps selection for the BEST attenuator. He claimed nothing was better. Therefore, it really won't be something I will ever need to repurchase.
-West
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LM,
aside from the choice of brand/type which I'm loath to offer an opinion on, the mechanical design of the switch is important. The pricey ones have high quality contacts, ball bearing shaft supports, heavy gold plating of critical contact points, wipers with spring mechanisms that don't weaken and are guaranteed for a number of life-cycles. This means they'll be working as well in 15 or more years time as they are now.
jules
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At the time I got my stepped attenuator from a Sydney supplier I did not know what I was getting but for about 60 dollars I thought it was worth the gamble. I was thinking I did not want to spend near half the cost of my GK(I have the very basic unit of the GK) on the TKD.
When I installed it I was surprised I could hear the improvement so I stuck with it. I then installed the sonicaps platinum at the 2 important spots - again the improvement was noticeable, however buck for buck the attenuator was a better buy, close to the same degree of improvement (?Change) for much much less money.
I have not gone back and taken it out and left the caps in to see how they affect the sound but sonic memory is such a deceiving thing I probably should?
Nor have I compared it to the TKD..........but I mustn't :nono:
Lyn you sound like you researched the attenuator a little and turns out it has half decent components in it.
Theo
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The other fact is that the TKD + Vishays was Bob Crump's selection for the BEST attenuator. He claimed nothing was better. Therefore, it really won't be something I will ever need to repurchase.
-West
Absoloootely! aa What satisfys (or I should say "satisfied"! :D ) the late, great Bob Crump is certainly good enough for me! aa
Many thanks to DSK for researching this great tweak! :D
Regards,
Andy
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LM,
aside from the choice of brand/type which I'm loath to offer an opinion on, the mechanical design of the switch is important. The pricey ones have high quality contacts, ball bearing shaft supports, heavy gold plating of critical contact points, wipers with spring mechanisms that don't weaken and are guaranteed for a number of life-cycles. This means they'll be working as well in 15 or more years time as they are now.
jules
This is a very good point as most tend to focus on the brand of resistors used and whether the attenuator series, shunt, or ladder attenuator, rather than the switch employed.
Elma uses 2 different 24 pole switches. The BV series is made for attenuators and does not exhibit noise bounce like the other Elma switch. DACT and Goldpoint both use Elma switches. Goldpoint uses the noisy one, not sure about DACT. Shallco and Seiden switches are more like Jules has mentioned. For the price, TDK had better be using very good switches!
Remember, the whole audio signal goes thru both the resistive element and the switch contacts in these attenuators. Which is the weakest link?
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Steve,
Your post prompted me to check the DACT site, since I have a DACT attenuator in an old Bottlehead Foreplay preamp that I might audition in the GK-1. DACT has some very specific instructions regarding cleaning the contacts of their switches and attenuators.
See: http://www.dact.com/html/contact_cleaning.html (http://www.dact.com/html/contact_cleaning.html)
Peter
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Peter,
I just read the DACT cleaning page. Interesting.
I suppose this could work, but may depend on what is causing the noise.
In my GP attenuator I have always had a bit of noise on one of the channels and not on the other. On the noisy one it has seemed dependant on contact pressure of the 2 contact points. At the moment it is just occassional, and not a big deal.
The BV series of Elma's come with an attached pcb. I think Goldpoint and Dact cannot use these. I've had a switch apart and looked at the contact points, and they look smallllllllllllllllllllllllllllllllllll lllllllll and thinnnnnnnnnnnnnnn.
But the only ways I know of to get around the switch contact issue is to use something like the Placette Audio attenuator, or GeorgeHiFi's lightspeed attenuator. I would think either of these might be a little difficult to implement into a GK-1.
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Steve,
Years ago I decided that a major weak point in any preamp was the level control.
That's when I figured that something of moderate cost would be best, but with the electrical environment optimised with low source impedance and high target impedance.
That was the genesis of the GK1 back in 2001; the other benefit of this approach was lower noise from the gain block since it's always working at full line level.
I discovered that SFernice made ceramic pots which sounded very good because the ceramic substrate was much harder and the multiple contacts thereby eliminated over the conventional carbon type. But SFernice (a small company established in Nice, the South of France) was absorbed by Vishay, the Philly based US company which also bought Beyschlag, Roederstein, and a host of other passive component manufacturers in the last 15 years, and the ceramic pots are no more.
Dammit.
That's when I went for the Panasonic EUWM, only available in motorised form and used in my Swift. These are very good.
I have been experimenting with shunt wire pots. They seem very good too, and this configuration can tolerate carbon pots without reduction in sound quality.
The switched attenuators are, some say, the ultimate, but they are a mechanically complex, miniaturised component, with so many moving parts, wear and friction is an issue and they do wear out. AND they are VERY expensive. The cheap Asian versions from Taiwan (MY3C.com) are really only durable for a few short years, as you would expect, but they look very nice.
Transformer attenuation to me is ridiculously expensive, and I cannot see the advantage, and I suspect that RF pickup could be an issue. Very bulky.
Cheers,
Hugh
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I can't resist. I've no idea how much these cost but they look the part ....
(http://www.audiocircle.com/image.php?id=14261)
the above is a Jos van Eijndhoven attenuator
and here's an Elma in an AKSA
(http://www.audiocircle.com/image.php?id=13537)
jules
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Jules,
Those implementations are amongst the best I've seen. LOVE the way the GK1 board is cut in two, then joined at the SS sections; wonderful - and the tubes are beautifully set up, LOVE it!!
The attenuator uses relays - an option I briefly considered but dismissed for its digital complexity and potential for hum. It's beautifully designed, I must say......... :drool: :drool:
Hugh
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Thanks for the compliment Hugh.
jules
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Jules,
that is truly jaw dropping. What a wonderful layout.
Is that some windows at the front of the tubes to see those babies glow?
Theo
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Thanks Theo,
yes, they're windows using curved pyrex glass ... must take some photos of the outside.
jules
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Jules,
Sorry I've been away for a few days and couldn't reply till now to your earlier post but quality switching does make sense. What does this item look like to you then http://www.acoustic-dimension.com/ (click on the 41 step attenuator menu item). Here is a review http://www.tnt-audio.com/accessories/stepped_attn_e.html Another item that looked interesting was here http://www.hificollective.co.uk/components/shinkoh_stepped_attenuator.html . I find this all rather fascinating but would have a very difficult time making any sort of informed decision on what to get if it wasn't for this thread. Perhaps Theo has the right option with a good value improvement even if it might not last forever. :?
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Lyn,
I'm away from home myself at the moment so there's a couple of details I can't put my hands on.
If you choose to build one it does save a little on costs. The one I chose, an Elma, is relatively easy to work on for soldering.
It's a slightly different model to the one from Percy Audio and the one you've found. I bought it direct from Elma USA. There are two layers of resistors in there [a total of 90 odd] and it can get fiddly.
The Acoustic Dimension looks great though both it and the model of Elma you've found look a little hard to work on. With 41 steps you're going to have to buy a stack of resistors and while it will give very small steps, my own experience is that 24 is more than enough.
There's quite a bit in the older Aspen posts on attenuators, including the suggestion that I might have overdone it :D. A search could be fruitful though.
Theo is probably right though :)
jules
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this is also not an expensive alternative from a well known source
(http://www.welbornelabs.com/images/remotebig.jpg)
RCA1 Remote Control Option 1 Kit $159.00
http://www.welbornelabs.com/remote.htm
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.....this is the option that I'm considering as part of my repackaging of my GK-1. Though only as volume control as I suspect that the source control part could be a tad fiddly to implement on the GK-1 output board..........maybe?
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Mmmm..
How do these compare soundwise to stepped attenuators. I assume they do not have a mechanical resistor step and work by electronic wizardry therefore would they degrade the sound in comparison?
Theo
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I went from a old passive pre with an Electroswitch ladder attenuator (offered by Sonic Frontiers years ago) to the Welborne passive with no sonic degradation that I could perceive. I switched passives because the Welborne has a remote control volume control :thumb:.
Cheers,
Tom
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Hi Theo,
No, premium quality resistors, with gold plated relay switching. The digital circuits you see are for the remote control function.
Strongly recommended. I deeply respect Ron Wellborne, and also Jim Hagerman, both incredibly good production engineers.
Cheers,
Hugh
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Thanks Kyrill,
Darn it. :duh: Just when I was thinking it was as simple as buying a DACT or similar high quality simple replacement item and that I’m quite prepared to give up a remote and couch potato status, you go and provide a further decision point. Sarcasm aside, thanks – more food for thought though. :thumb:
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Just to keep the stepped attenuator discussion on this thread.
I have researched as best I can, the bulk of the Stepped Attenuator options available to me. The overall prices for good quality switches seem to range from about $150 to $250 landed in Oz (TDK a bit more) so for convenience, perhaps the 20kOhm DACT at $195 sourced from an Oz distributor is reasonable. I must admit that I agree with Hugh and Theo here, not cheap so I hope, well worth it. Makes cap upgrades other than the Platinum seem a positive bargain.
My only remaining concern is that even with my relatively inefficient Vanderstein’s at moderate to high volume, I rarely have the original volume control pot turned beyond about 90deg from ‘off’ out of the approximate 280deg rotation available. In fact, that’s only with the phono selected and it’s rarely beyond about 45deg with CD selected, such is the gain and grunt of the Soraya. I’m just a bit concerned that after looking at the DACT specs, I’ll be in the courser 4db or more per stop attenuation area for common listening levels. What do those who have fitted a DACT or other SA say? Am I concerned over nothing or should I look at other options?
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Just to keep the stepped attenuator discussion on this thread.
I have researched as best I can, the bulk of the Stepped Attenuator options available to me. The overall prices for good quality switches seem to range from about $150 to $250 landed in Oz (TDK a bit more) ...
You get what you pay for, Laurie.
The TDK is a lot more ... when I bought it in late 2006, it was USD250 then there were the 4 Vishay S102 bypass resistors at USD30 each. I suggest if you don't go for the "ultimate" (TKD plus Bob Crump's S102 bypasses) then you may as well go for a non-TKD attenuator ... which will be much cheaper.
If you want your GK-1 to remain in your system for a very long time (ie. so it can't be bested under $10K! :D ) ... go for the TKD/Vishay combo.
Regards,
Andy
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One of the other benefits of the TKD is that it has 40 steps of 0.5 to 1dB.
In late 2002 I was trying to figure out whether to go with DACT, a Goldpoint ladder or something else in my GK-1. I exchanged a number of emails with the late, great Bob Crump on the matter. He had spent some years evaluating just about every attenuator under the sun, including pots, shunts, series and ladders with a variety of resistors and bypasses etc etc. In the end, the TKD with S102 bypasses was the best he found and it became the attenuator of choice for the cost no object CTC BlowTorch pre-amp (~US$15k). I believe it was also used in the $$$$ LAMM Reference 2 (I think that was the model). Bob's advice was that if I was considering an attenuator solution anywhere the cost of the TKD/S102 combo, I may as well spend the bit extra and get the best. He also advised that he had tried a large number of different bypass resistors but none approached the Vishay S102 on the TKD. After a series of emails with Bob through 2003 I eventually pulled the trigger in March 2004 and did just that.
A word of warning though, it does need a fair bit of space to mount and it mounts with 3 machine screws through the front panel (hidden behind the volume knob). It also has a fairly lengthy break-in period to sound its best, though Hugh and I thought it sounded excellent from new. I heard a while back that the price had gone up even further and Michael Percy wasn't going to stock them any more as a result. However, last I heard they were still available from Japan where they are made.
How much better does it sound than the likes of the DACT or GoldPoint ladders etc? I have no idea. I didn't have the time, money or energy to repeat for myself the evaluation studies performed by Bob. I trusted Bob and have never regretted it.
(http://www.audiocircle.com/image.php?id=14557)
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Found on web: http://electronics.dantimax.dk/Kits/Selectors_-_attenuators/index.html
A lot of different options available and prices are very good too :D
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Found on web: http://electronics.dantimax.dk/Kits/Selectors_-_attenuators/index.html
A lot of different options available and prices are very good too :D
If the prices are attractive, why not just take the cheapest? At least there's some logic behind that decision! :o
Oh, wait - why not keep Hugh's volume pot and not spend anything! :D
The problem with the ones listed is that no-one has compared them in an exhaustive shoot-out ... so it's a crap shoot as to whether they will actually make your GK-1 sound better. With the TKD (yes, unfortunately the most expensive option!), we are taking advantage of Bob Crump's work in finding the best-sounding attenuator for his very expensive preamp.
Regards,
Andy
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Oh, wait - why not keep Hugh's volume pot and not spend anything!
No Andy :nono:, I didn't want to hear such good advice though I suspect Hugh and my wife would agree.
The TDK is still $249 (US) in the current catalogue though with no 20KOhm option (10 though) so theoretically available but if you will forgive my ignorance, exactly why are the bypass resistors needed?
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The TDK is still $249 (US) in the current catalogue though with no 20KOhm option (10 though) so theoretically available but if you will forgive my ignorance, exactly why are the bypass resistors needed?
Because Bob Crump told DSK that using them improved the sound, over a "bare" TDK. :D
Regards,
Andy
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Hi Andy,
I got the ‘best sounding’ bit but my question as a non-engineer (and general ignoramus) was that I didn’t understand what needed to be bypassed. Is the TDK not a good enough SA in its own right? Would bypassing apply to other SAs?
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Just to keep the stepped attenuator discussion on this thread.
I have researched as best I can, the bulk of the Stepped Attenuator options available to me. The overall prices for good quality switches seem to range from about $150 to $250 landed in Oz (TDK a bit more) so for convenience, perhaps the 20kOhm DACT at $195 sourced from an Oz distributor is reasonable. I must admit that I agree with Hugh and Theo here, not cheap so I hope, well worth it. Makes cap upgrades other than the Platinum seem a positive bargain.
My only remaining concern is that even with my relatively inefficient Vanderstein’s at moderate to high volume, I rarely have the original volume control pot turned beyond about 90deg from ‘off’ out of the approximate 280deg rotation available. In fact, that’s only with the phono selected and it’s rarely beyond about 45deg with CD selected, such is the gain and grunt of the Soraya. I’m just a bit concerned that after looking at the DACT specs, I’ll be in the courser 4db or more per stop attenuation area for common listening levels. What do those who have fitted a DACT or other SA say? Am I concerned over nothing or should I look at other options?
Hi LM,
In my system I only had Hughs Alps pot at around the 9 o'clock position at my normal listening level. In other words hardly off the stop. With the DACT it's up around the 11 o'clock position. I seem to recall Hugh saying he'd changed the pot he supplied in the kit so yours might not be the same as mine though.
Cheers
CJ
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Thanks CJ,
Yes, often mine is hardly off the stop (many of the latest compressed CDs) so that sounds promising. I was hoping the finer steps would be in my normal listening range. Cheers
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Hi Andy,
I got the ‘best sounding’ bit but my question as a non-engineer (and general ignoramus) was that I didn’t understand what needed to be bypassed. Is the TDK not a good enough SA in its own right? Would bypassing apply to other SAs?
Hi Laurie,
Bob C thought, yes, the TKD is an extremely good-sounding SA. However, by playing around (as he certainly knew what he was doing!) he was able to make it sound better. :D I believe (DSK might be able to confirm?) that these bypass resistors act to almost take the attenuator out-of-circuit. In which case, you might well ask ... why bother to use an expensive TKD attenuator!!?? :D
I would suspect that "the bypass trick" would make any other attenuator sound better ... but Bob found the TKD sounded the best out of the ones he tested.
By all means buy half a dozen SAs and experiment for 2 months each (as Bob did). After all, there are probably some SAs available now which weren't around when Bob did his tests. I didn't have the time to do this - so I went "Bob's route"! :thumb:
Regards,
Andy
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Hi Andy,
I got the ‘best sounding’ bit but my question as a non-engineer (and general ignoramus) was that I didn’t understand what needed to be bypassed. Is the TDK not a good enough SA in its own right? Would bypassing apply to other SAs?
Hi Lyn,
The TKD is fine on its own (it likely would not have survived as a product at that price otherwise) but in his never ending quest for "the best" Bob tried every mod he could think of. Primarily, he found that these bypass resistors improved dynamics.
Yes, the bypass mod could also be applied to other 'series' type stepped attenuators too, but you would need to experiment with various resistors to see which sounded best (to you). Originally I considered using some Caddocks (not cheap but much cheaper than the S102's) but Bob had tried them on the TKD and felt they sounded "crap".
EDIT: For those not aware, CTC was the team of Curl/Thompson/Crump. In this team, Bob Crump was the "parts guy" who scoured the world for the best sounding parts for their cost no object designs. The TKD/S102 setup was the closest thing to a totally transparent attenuator he could find. Theory may suggest that a 'ladder' type attenuator should be more transparent than a 'series' type, but this is not what Bob's testing found. As AndyR said, the bypass resistors effectively "bypass" the resistors in the attenuator to a large degree, thus improving dynamics and transparency.
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Thanks all, my previous lack of knowledge has been successfully redressed. :thumb:
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Regarding the Welborne attenuator.
I have one installed in my GK-1, and I can confirm that it does work. however, there is a subliminal feeling that if anything in the preamp is to be improved, this is it. It is a shunt attenuator, i.e. it shunts the signal through the IC to ground. The series resistor is a Vishay/Dale metal film of good quality. I haven't compared it directly to anything else, as the GK-1 was built with this from scratch. I previously ran a pre-amp with a passive line stake with a switched attenuator which was a significant improvement over a log-faked Sfernice cermet pot.
There are some idiosyncrasies with the operation, but these may have been sorted out with later revisions. I also couldn't get one channel to work initially and had to send it back to Welborne. I never got an explanation of why it didn't work, but it came back with an additional cap inexpertly soldered across two legs on one of the IC's; I had to resolder it as it had come loose in transit.
I have bought from Welborne several times, with very little hassle. However, support is cursory at best (the antithesis of Hugh) and several people on AA have reported non delivery of orders in recent times. This is something any potential purchaser needs to be aware of.
I have recently looked at the relay switched attenuator kits from Bent Audio (http://www.bentaudio.com/index2.html) and Twisted Pear (http://www.twistedpearaudio.com/joshuatree/jt.aspx) as alternatives, but haven't progressed beyond this yet. They may be worth investigating as well as alternatives to the TKD and others, particularly if remote operation is required.
Regards
Mike
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Thanks Darren, Mike,
This is extremely interesting information......
Cheers,
Hugh
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Hi Andy,
I got the ‘best sounding’ bit but my question as a non-engineer (and general ignoramus) was that I didn’t understand what needed to be bypassed. Is the TDK not a good enough SA in its own right? Would bypassing apply to other SAs?
Hi Lyn,
The TKD is fine on its own (it likely would not have survived as a product at that price otherwise) but in his never ending quest for "the best" Bob tried every mod he could think of. Primarily, he found that these bypass resistors improved dynamics.
Yes, the bypass mod could also be applied to other 'series' type stepped attenuators too, but you would need to experiment with various resistors to see which sounded best (to you). Originally I considered using some Caddocks (not cheap but much cheaper than the S102's) but Bob had tried them on the TKD and felt they sounded "crap".
Hi Darren,
I'm not at all interested in a new attenuator. But I'm interested in learning about the "bypass" associated with the TKD. From a post up above, I learned that its 40 steps in the 0.5 to 1.0 db area. This helps explain much of the high cost. But what are you doing with the bypass stuff? Are you making some kind of fancy fake shunt attenuator? You don't have to divulge any proprietary secrets of course, but a couple words can explain a lot.
Steve
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I agree with Hugh’s thanks for all the interesting thoughts and options, more grist for the old mill.
Now we appear to have a couple of options for some relay based attenuators (AKSAphile the Dantimax RelVol1 and MikeC the Twisted Pear Joshua Tree). Where would such items fit in sonic wise with the various series, shunt, ladder, bypassed etc SA’s that have been discussed so far?
:duh:
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Well if Bob Crump was right the bypassed TKD would be better than the rest of the types of volume controls. I believe he didn't just try stepped attenuators, but tried everything available at the time. Therefore the bypassed TKD is superior to all. However, I’m not sure how another stepped attenuator would fit into the mix, but I would speculate a stepped attenuator is better than digital volume control.
Also, Steve, I'm not sure if this is what you are looking for, but the TKD is bypassed from input to output with resistors that are 10x-12x ohms the stepped attenuators. 10k stepped attenuator = 100k-120k resistors. That is the basics on the mod itself, although I'm not sure on what it technically speaking does.
-West
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Also, Steve, I'm not sure if this is what you are looking for, but the TKD is bypassed from input to output with resistors that are 10x-12x ohms the stepped attenuators. 10k stepped attenuator = 100k-120k resistors. That is the basics on the mod itself, although I'm not sure on what it technically speaking does.
-West
West,
If I read the above correctly, then why would 4 resistors be required, rather than 1 per channel?
But really, since I don't want to do any of this, the answer doesn't matter. I was just curious.
Steve
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Lynton mentioned 'grist for the mill', but I have one more to throw in here.
The sonic problems of potentiometers derive from the multiple contact phenomenon of the wiper, and they essentially rob resolution at very low levels. The switched attentuator replaces a continuously variable carbon or plastic track with a ladder of resistors, where the only degradation is in the solder joints and the switching points. This is known to be much 'cleaner', but there is still the problem of high cost, limited availability (or at least convenience of purchase), and highish wear rates, which knocks out the cheaper Asian imports.
The Rolls Royce (now there's a fading metaphor!) of switched attentuators is undoubtedly the Japanese TKD, which is veritably a scientific instrument, made like a Honda F1 engine cylinder head. Just to hold it in your hand is a feeling of wonder, or at least for odd characters like myself who absolutely live for good engineering!! But the cost is absurd, something you would only entertain for a $20K+ preamplifier. That my GK1 is considered in this rarified company is a great flattery, and I'm pretty happy about it!
The Welborne Labs relay system is good, but I would suggest that the relay quality is the pivotal factor here, and they may be cheapies. My favourite is the NAIS Aromat, with silver/palladium contacts, which is supplied in my Swift. I've never heard any degradation of the signal using these relays, but I don't believe they are used in the Welborne kit product.
This third relay approach, wherein the complex, 24 position switch is replaced by several relays under microprocessor control driven from a rotary selector is pretty good, but it's electrically complex, and a whole project on its own to build. I quite like it, and a Norwegian called Kolbrek (IIRC) created a marvellous design later added to by a clever young Viennese EE student, now graduated, with the interesting name of Timo Christ, which is a full on DIY project somewhere on the net.
However, since about 2002 when I designed the GK1 there have been a slowly growing list of microprocessor controlled ladder attentuators apperaing in the market with integrated opamp outputs for buffering and laser trimmed resistors. The most famous is the PGA2310, originally a Burr Brown chip, now owned by Texas Instruments. This product appeared in Oct 2001 but was revised in Sep 2004, and has stellar specification, namely -95dB to +31.5dB in 0.5dB steps (!!!), a distortion figure PLUS noise of just 0.0004%, a Zout of around 100R, a dynamic range of 120dB, and a unity gain bandwidth of 1.5MHz. With a Zin of just 10K, two independent channels on the one chip, and noiseless switching, this is surely just the ticket for a premium quality high end system.
Other chips have since appeared in the market, I believe.
More grist for the mill? :lol: :lol: :duh: :duh: :drool: :drool:
Ciao,
Hugh
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Grist!! That's evil Hugh :)
So at $9.95 for a PGA2310, what's the catch and where does the cost come in?
jules
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The Rolls Royce (now there's a fading metaphor!) of switched attentuators is undoubtedly the Japanese TKD, which is veritably a scientific instrument, made like a Honda F1 engine cylinder head. Just to hold it in your hand is a feeling of wonder, or at least for odd characters like myself who absolutely live for good engineering!! But the cost is absurd, something you would only entertain for a $20K+ preamplifier. That my GK1 is considered in this rarified company is a great flattery, and I'm pretty happy about it!
Hugh,
My personal thinking is that the main component in any preamp is the pot or the attenuator, and then the selector switch. The reason for my thinking this is that those are the only two parts I believe serve a purpose. However, the Gk-1 is special, and it adds tubes. I too purchased 7308s, so at this point the only thing that I have really left alone is your circuit, and from what I hear...it deserves all these amazing parts. I, in my mind, have created the ultimate preamp (TKD + DACT) and then the your wonderful tube circuit makes it everything I could ask for. It is all 'clean and pure' and then your GK-1 adds life and makes it special. Even the best circuit sounds bad with bad parts, so if you take the best circuit and add the best parts...
That is why I got the TKD, DACT, 7308, and Platinums (and soon Solens).
-West
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As an electronic solution then, I sure hope a voice control circuit could be added. Asking my GK1 to set –40db would sure save a lot of effort in looking for the misplaced remote.
On a more serious note Hugh, is this the sort of circuitry underlying the Volume control on my Arcam AVR and perhaps for other brands that have moved on from the old motorised ALPS Blue Velvet or similar. It certainly has a lovely feel and has a full logarithmic range display. If so, are any such complete chip based volume control assemblies available commercially and at reasonable cost for GK1 fitment. :D
Edit: Answering one of my own questions, Arcam appear to use the LM1972 from National Semiconductor. Still haven't found any 'commercial' package or kit though but will keep looking.
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Google turned up this one:
(http://electronics.dantimax.dk/Kits/Selectors_-_attenuators/Foto/ChipVol1-3.180_250.jpg)
http://electronics.dantimax.dk/Kits/Selectors_-_attenuators/index.html - ChipVol1
They have a PGA2310 chip attenuator, a relay attenuator and motorised pots, with controllers with or without displays and remote control.
Cheers,
Ron
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The Welborne Labs relay system is good, but I would suggest that the relay quality is the pivotal factor here, and they may be cheapies.
The input switching on the Welborne kit is by relays. The attenuator has a series resistor in conjunction with an IC shunt attenuator. I'm not sure what the IC is as all markings have been scrubbed, but the total range is only 36dB (60 steps of 0.6dB each). One of my issues with the kit is the limited range - volume setting invariably not low enough on some highly compressed recordings, and can't get high enough with really dynamic recordings. As I said, I will be changing this at some stage, I just need to find something that will work within a casing optimised for remote switching and volume control. A rotary attenuator and/or input selector will require a completely new preamp case, so the TKD is disqualified, unless I can work out a stepper motor drive and display driver for it.
There are some kits becoming available that look like they may fit the bill for me. I really like the look of the Bent resistor (not Tx) kit, but the control board will not fit my case, and it is a bit pricey. The re-designed Twisted Pear should also work, and the Dantimax kits mentioned warrant some investigation.
I think I smell a new upgrade kit from Hugh here :wink:
Mike
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They have a PGA2310 chip attenuator, a relay attenuator and motorised pots, with controllers with or without displays and remote control.
I missed the 2310 based kit at this site earlier so thanks Ron. I must admit the appealing bit here (to me) is the fine adjustment provided by the 1db steps over the whole usable attenuation range. No worries about being caught up in the relatively course steps of the DACT or similar in the -38db attenuation or greater region, even if such fine steps are of little practical use below about -60/70db,
Now the only problem I personally have is whether I should try going that way or go with a more straightforward DACT etc. install. I feel I would have no problems assembling/soldering such a kit but would need advice in ensuring that I had ordered all of the other ancillary kit/components etc to make the package work, particularly with options like remote control. :)
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WOW!! :drool: :roll: Thanks Ron, this is a pearler from Dantimax, and inexpensive, too!!
It's beautifully engineered from the pictures, and when you realise there are several hundred lines of machine code in the software, it's an absolute bargain!
Thanks West, very nice of you..... you are very positive, I appreciate it.
Lyn, we shall speak tomorrow, but in truth you need no more than 1dB steps, and while a range of 40dB is acceptable, 50dB is better, as Mike has suggested.
Not sure I can do one of these cheaper...... I like the Dantimax, I really do. :drool:
Cheers,
Hugh
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Well...PGA 2310 is of course one of the best "digital" volume attenuators available today. It has many advantages over mechanical volume controls such as very high precision, crosstalk, almost unlimited life, but...as any other thing in EE the PGA 2310 has also some disadvantages compared to normal potentiometers.
We shouldn`t forget that PGA2310 is not a passive volume control, but an active, since it has opamp output buffer to lower output impedance. This is not a major concern, but the question is how good is actually this buffer opamp? BurrBrown (TI) never described in their datasheets which opamp they use. Some folks are sure that PGA 2310 has OPA2134 or OPA2604 on the output. These opamps are very good, but not the best to today standards. :?
Few weeks ago I spend a lot of time upgrading my CD player output stage, testing and comparing various opamps from OPA2604, OPA2134 to the latest National LM4562. All the people that were with me during listening tests, confirm my opinion that LM4562 is SEVERAL times better than his BurrBrown competition. It sound is more like to high class discrete design, not opamp. When I put opa 2134 /2604 back to chain I quickly realize that these chips are not totally transparent and they compress sound. I now threw away my opa2134 preamp gain stage and I simply use just 10k Alps pot between CD and AKSA and music just flows naturally. (with LF this should be probably much more evident :P)
I have not tested PGA 2310 yet, but with these listening experiences, I am afraid that PGA 2310 cannot be the purest volume control available. It has a lot of pros, but I think that for high end reproduction, where purity is essential, nothing can beat stepped or relay volume attenuator. 8)
BTW: One of the most popular audiophile integrated amplifier - Lavardin, still uses blue ALPS... aa
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Thanks Andrej,
I can agree with all your points, but, as you say, the pros and cons of these devices must be weighed up.
I see it this way. The spread of distortions introduced by premium quality electronics in the front end are below about 0.001%, and if we use tubes, the distortions they introduce in open loop are all low order, and high, around 1% minimum, and more likely two or three percent. The Cathode Follower used on the GK1 introduces these levels, all H2 and H3, nothing higher, and these colorations, which are responsible for the 'sound' of the GK1 (detailed yet warm and engaging), dwarf the tiny but objectionable distortions of the preceding solid state stage.
We are reaching a point in the technology where people will not buy a product without a remote, and this requirement forces either a motor driven pot (expensive and flawed) or a digital pot in an IC (cheap and flawed)!
In the early nineties ABS was made available on some automobiles as sold as a safety feature. Now, it is mandatory, and I see preamps going the same way - if they survive in their present format, that is.
I'm surprised the Lavardin uses the blue ALPS, I would have expected the black version, or even a DACT!!
I would like to see a Taiwanese company produce an all smd, laser soldered attentuator, using teflon substrate. It should be durable, self lubricating, and sonically wonderful. The problem is one of quantity and ROI. It's not a difficult design problem.
Thanks for the contribution. You give an EEs perspective, very interesting and informative.
Cheers,
Hugh
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Thank you Hugh for nice comments...
I 100% agree that in case of GK1 preamplifier, PGA 2310 should perfectly sit between solid state and output valve unity gain stage. PGA`s harmonic distortion is several times lower that typical valve and you got remote too. Ideally PGA should sit directly on GK1 board eliminating several signal wires. I would call this musical or joy solution. :)
In the case of passive preamp, I would rather put relay volume control there and you can have it remote controlled too... :wink:
About Lavardin...I was also surprised about use of standard blue Alps option, but here is the picture...
(http://img138.imageshack.us/img138/7734/lavardinww3.th.jpg) (http://img138.imageshack.us/my.php?image=lavardinww3.jpg)
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Very interesting thoughts AKSAphile.
On another tack though, does anyone know where else one might obtain a TKD attenuator other than M Percy?
Going right back to the opening post, the 20KOhm version is no longer in stock at that site but I’m sure it has to be available somewhere and at a broadly equivalent price. If so, I could optionally go the TKD way (perhaps at first without the Vishays and then update later with more budget). But if I did so, I would ideally like to get the 20KOhm version. Whilst the forum could undoubtedly help me choose resistors and setup etc to optimise use the 10KOhm version, I would prefer the simpler route. This would apply particularly if I had to experiment with optimising the system gain. At least I can always get 20KOhm and 25KOhm options from Goldpoint and DACT without any extra considerations applying and Goldpoint has some good tables on its site dealing with the resistor values needed for such adjustments.
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It has been a long time but I seem to recall that the TKD was available directly from TKD in Japan.
Also, I recall that www.thlaudio.com (http://www.thlaudio.com) had them.
It is the 25K version that I use with 250K Vishay S102's.
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Thanks Darren,
Great information!! There are many pots offered by TKD, but for those interested in chasing it up, it's this model:
2P65S TKD Step Attenuator
Round, stereo, Best rotation 315°, 25 x 25mm, 19.5 mm(L),
Ohmic law type A( log)
Impedance: 10K, 20K, 50K, 100K, 250K & 500K
Installation triangle hole(center to center): 28 mm
Shaft: 6 mm dia.
For best results on the GK1 choose the 20K version.
Cheers,
Hugh
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Thanks also Darren.
Guess from looking at the TKD pdf, a 2P65CS20KOhm would be the complete description. Interestingly, the S (or blank) is for 'click' or not and it seems to me a click would be useful. Just wondering what you had Darren. No price list at those sites so an enquiry is will be needed to ascertain the damage.
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Thanks also Darren.
Guess from looking at the TKD pdf, a 2P65CS20KOhm would be the complete description. Interestingly, the S (or blank) is for 'click' or not and it seems to me a click would be useful. Just wondering what you had Darren. No price list at those sites so an enquiry is will be needed to ascertain the damage.
Yes, Darren and I have the "click-stop" version (an excellent feature BTW).
We bought the 25K version (stereo) but maybe this is no longer available? :?
Regards,
Andy
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I asked THL about their prices before going with the 10k TKD from Michael Percy.
They charge 17500NT (they say NT, but its the same as TWD) which is about $575. Michael Percy is $250, and the price doubled on him, so he is selling them to us at a GREAT deal right now. If you want a TKD...now is the time to buy. I asked if he could get a 25k TKD, and he explained it would really cost around $500+, which is why I just stuck with the 10k.
They were also out of stock on the Vishay S102 250kOhm. Michael Percy is again, in stock, and also if you go with the 10k TKD you only need to use 120kOhm Vishays, which are once again, cheaper.
Hope this helps.
-West
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I've emailed TKD so we'll see if direct is an option and at what price.
Funny how good my original pot is sounding right now compared to a $500 option. I'm sure 10KOhm is a good option.
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Yes, as AndyR said, we have the 25K version with the clicks (Steps). It is quite useful in returning to the same volume level (eg. when A/B'ing etc).
THL never listed the 25K version, even back when I was buying mine. I did approach TKD directly (http://www.tkd-corp.com/02_products/p_04variable_a.html (http://www.tkd-corp.com/02_products/p_04variable_a.html)) and received prompt and courteous responses. IIRC their pricing was similar to Percy and I think I may have gone with Percy as he could also supply the S102's.
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West,
Wondering if you have received and fitted the10KOhm TKD and bypass resistors yet and if so, what you think.
I still have the same dilemma as before. TKD got back to me and the cost of their attenuator ex factory is about 30% higher than the M Percy ‘old stock’ price. Not unreasonable if I ‘must have’ the 20KOhm version however the other bad news is that the manufacturing lead-time (at least for the 20KOhm version) is a month and a half. Hugh says that whilst the 20KOhm is ideal, a 10KOhm would be OK and it certainly is cheaper. My budget covers a DACT (or similar) right now but could stretch to the 10KOhm TKD now to use ‘as is’. However, this allows the possibility of the Crump/Vishay upgrade later as I know that you, Andy and Darren recommend.
So what I would like to understand, given my lack of electrical knowledge, is that given that 20Kohm is ideal but a 10KOhm perfectly OK, is the 20 worth the solid price premium that would largely pay for the bypass resistors if I ever go that way? Clearly, Andy and Darren bought 25KOhm versions, not 10. Secondly, might the careful choice of bypass resistors in the future restore optimal 20/25KOhm matching or am I really showing my ignorance here? Note: M Percy will be on holidays soon so ideally would like to make my mind up quickly. :duh: :duh: :duh:
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I'll leave it to Hugh to explain the sonic differnce between 20k and 10k, but I doubt its very noticable at all. Doubt its worth the 30%.
I have recieved TKD and resistors but haven't yet been able to hear it. My GK-1 is sitting on my desk and I've just gotten it built today (the board that is). I've still got to fit all the components (amps/asp/gk-1) into cases and wire them...oh and build the orions...before I get to actually hear the system. :x Hopefully that will be sometime soon. I'm going to post a build thread in a bit.
Also the mod didn't have to do with the fact it was 20/250, it had to do with the resistor being 10x to 12x the TKD value.
Hope this helps!
-West
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Also the mod didn't have to do with the fact it was 20/250, it had to do with the resistor being 10x to 12x the TKD value.
West,
Hugh has said 'not much difference' to me. He may care to elaborate but essentially said this at a very early post
It does help but perhaps pretty clumsy wording from me for the 20 to 25K Ohm bit. I suppose to put it another way, I simply want to be sure that accepting the 10K option now won’t be any cause for regret later that I should have paid the premium for the 20K version. Clearly, you have decided it will be OK.
Also, I haven’t seen any diagrams on what is involved with the bypass upgrade so I have no clue as to what change if any they would make to the overall volume control impedance. I have looked at cct diagrams on the Goldpoint site about applying resistors at varying points to the input and output sides to change the SA response to better suit high or low gain amp situations and I wasn't sure if there would be any such considerations to look for in selecting resistors. Its just another reason why an SA alone for me is such a simple start point.
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LM,
I too asked Hugh about the difference between 10k vs. 20k and he said it wasn't much at all. So I wen't ahead I got the 10k, as I think it was worth the 30% discount.
Hugh,
Would you mind explaining the exact difference of 10k vs. 20k? How will the sonics be changed?
-West
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West,
No difference at all - the Zout of the SS section is just 32 ohms, so 10K, 15K, 20K, it's mere bagatelle for the driving circuit.
Cheers,
Hugh
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Well I went ahead and ordered a 10KOhm TKD from Michael Percy last Friday week and received it on Wednesday. Also ordered some Solens Caps as well though that’s a matter for another thread. Had all the new components fitted on Thursday and wired back in to my set-up on Friday night. Overall sound I’ll discuss in the GK1 thread but the TKD is certainly a beautiful instrument; I see now what Hugh and others have been commenting about so thanks to all that suggested it.
The taper is absolutely fabulous and with 40 positions, no problem whatsoever in finding a suitable volume position. The feel is precise and sound as clean as a whistle. I’ll keep the advice about Bob Crumps improvements in mind but at least for the time being, I am perfectly satisfied with using the attenuator stock or as is. Couldn’t recommend it more highly even though it has a bare 5 hours bedding in and I suspect there is much subtle improvement to come over the next few hundred hours or so.
:thumb:
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... Couldn’t recommend it more highly even though it has a bare 5 hours bedding in and I suspect there is much subtle improvement to come over the next few hundred hours or so.
:thumb:
Bob Crump's words were "... approx 45 days of 24/7 ..." to fully break in! I didn't bother keeping track of hours. Like you, we heard an instant improvement from the TKD alone (then another smaller but worthwhile improvement when we added the S102's shortly after). I must say that with no other changes, the GK-1 sounded a little better (to a degree that only an owner would probably notice) a few months later ...my system gets nowhere near 24/7 play time. Bob felt that the S102's improved dynamics and transparency.
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Bob Crump's words were "... approx 45 days of 24/7 ..." to fully break in!
That's both horrible news in the sense of ' I hope I can control my impatience' and great news in that 'you mean it gets better than WOW!'
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Is that at each output step? :o
Nick
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Is that at each output step? :o
Nick
No, it is not a ladder.
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RonR,
I like all the others around here have really appreciated your efforts on another thread to test the various Cap options at C4/C7 etc but I was wondering if you had any worthwhile observations about the TKD you fitted that you could add here. :D I ask because you say you repeated the tests after replacing your original Vishay stepped attenuator and I would love some clue as to nature of the TKD changes.
I know it was not what you tested for but I’m curious because I changed both the caps and attenuator at the same time and unless you can shed some light, will always be wondering what contributed what to the improved sound. :duh:
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Lyn,
After putting the TKD attenuator in circuit I found precision / detail improvements, and also a better frequency balance, as though the response was "flatter" somehow.
My naked Vishays have now arrived, so I'm about to embark on the Bob Crump mod.
Question: Have any of you guys opened the TKD metal case and fitted the resistors inside? Those naked Vishays look very delicate, and I'd hate to trash one while fitting the attenuator in a case!
Cheers,
Ron.
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Inside? I thought they went on the outside.
-West
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Hi Ron,
My suggestion: put 'em on the outside of the case; you probably need three company certificates and a nice white coat to open the case on a TKD. Scientific Instrument, y'know!!
Hugh
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Just to throw an additional cat amongst the pigeons.
For a manual stepped attenuator I would consider this one from John Broskie.
http://glass-ware.stores.yahoo.net/tcj-stepped-attenuator.html
Its a little weird in that it has a central switch which switches left and right channels in 11 "coarse" 6dB increments and then the left and right switches give 6 1dB increment "fine" adjust for left and right channels respectively - thus you also get a "balance" option for free.
The net result is 66 attenuation levels in 1 dB steps.
Its a combination series and ladder attenuator. Basically the coase adjustment is done using the series resistors and the fine adjusts are ladder style.
$US160 PLUS resistor cost (you can fit what you like).
Using JB's "standard" resistor value options the Zin is 50K BUT you can scale up or down easily.
The series resistors will be more important than the ladder resistors to sonic results so you can even target the audio jewelry components to these positions.
Cheers,
Ian
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Hi All,
The Crump mod finally made it into my GK-1. I used 120k Naked Vishay resistors on the outside of the metal case of my 10K attenuator.
TBH I did don my white coat and take a look inside the case, but I wasn't comfortable with shoe-horning the resistors in there.
After a couple of days I can say that the transparency has increased.
Cheers,
Ron
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Hi Ron,
I never doubted the AndyR and DSK faith that the Crump mod would be a further improvement over the stand alone TKD but it’s very interesting to have it reconfirmed. I must say the unmodified item is a corker so this must be some pretty nice icing on the cake.
My question though is has it changed the stepped output in any noticeable way? I have found the taper of the 40 or so steps of the standard item near perfect in my system. I can always find the ideal volume and it’s generally at about the 10/11 o’clock position on the control for normal listening volume.
It would also be interesting to know just how much the overall attenuator rating changes from the original 10K due to the mod, perhaps by measurement or calculation. This may not matter but as I said, more for interest than anything else. :)
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...
It would also be interesting to know just how much the overall attenuator rating changes from the original 10K due to the mod, perhaps by measurement or calculation. This may not matter but as I said, more for interest than anything else. :) ...
Hugh advised it was OK to replace the stock 25K pot with a 10K TKD. Surely that change must be far more significant than any impact the bypass resistors would have so I think you're right that it probably doesn't matter much.
However, like you I am interested. Hugh ... is there a way to calc the change produced by adding the bypass resistors?
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Hi guys,
I didn't detect much change in the way the attenuator functions, just 1 or maybe 2 clicks more were required to give the same sound levels as before.
I measured the bypassed attenuator at zero volume and full volume positions before installation. At zero volume the input to earth/output measurement was 9.22k, and at full volume the input/output to earth measurement was again 9.22k. I'm afraid I didn't measure the effect at other positions.
Cheers,
Ron
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My question though is has it changed the stepped output in any noticeable way? I have found the taper of the 40 or so steps of the standard item near perfect in my system. I can always find the ideal volume and it’s generally at about the 10/11 o’clock position on the control for normal listening volume.
My question is, Lyn ... what does it matter? If you used to listen at 10/11 o'clock then if (as RonR says) it takes a couple of clicks more to get the same volume ... you're listening at 10:30/11:30 o'clock. And so? :?
For tuner & CD, I listen at 12 / 1 o'clock for "normal" sound levels. If I want to crank it up, it's 2 o'clock - or a click or two more.
For phono, because I feed my LOMC directly into my upgraded-gain MM stage, I listen at 3 o'clock or 3:30. Sometimes if the LP is cut low and I want to listen loud ... I listen at 5 o'clock - which is as far as the TKD will go - ie. it's out of circuit.
Regards,
Andy
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just 1 or maybe 2 clicks more were required to give the same sound levels as before
Hi Ron,
Thanks, exactly what I wanted to know, appreciated.
My question is, Lyn ... what does it matter?
Hi Andy,
I must admit I’m rather intrigued by your question. :scratch: Following Ron’s answer and your confirmation, clearly it does change things in a noticeable way but I agree, not enough to matter. The first part is the answer to my question and second is the answer to yours. And so?…. I’m happy. :thumb: aa
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if you want one of the best stepped volume controls :drool:
http://www.tentlabs.com/Products/page31/page31.html
Guido Tent and associated are well respected EE's only interested to be one of the best in his high end audio applications
(http://www.tentlabs.com/Products/page31/files/page31_1.jpg)(http://www.tentlabs.com/Products/page31/files/page31_2.jpg)
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if you want one of the best stepped volume controls :drool:
http://www.tentlabs.com/Products/page31/page31.html
Guido Tent and associated are well respected EE's only interested to be one of the best in his high end audio applications
(http://www.tentlabs.com/Products/page31/files/page31_1.jpg)(http://www.tentlabs.com/Products/page31/files/page31_2.jpg)
This is really one of the sexiest volume controls available ...:drool:
...but good things don`t come cheap :(
Tentlabs said that there should be soon available volume control with added buffer :drool:
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I was just taking a look back at this thread, and while I do think the Tent Labs volume control is very nice, wouldn't it be a bit of a pain to use with a Gk-1? I mean I feel like it would either be one more RCA interconnect (which in my mind is bad) or it seems like it would be a bit complicated to incorperate into the system...
I am personally very satisfied with my selector and attenuator, but it is true that this looks VERY nice. I would love the ability to use a remote with my GK-1 and still have a good stepped attenuator and selector. I'm still not sure if this compares to the bypassed TKD, might be very close!
-West
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Go on Westy ... somebody has to be the first .... :lol:
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West,
I'm confident that Guido's RSA could be hard wired into the GK1 without difficulty.
Don't know the cost, probably 100 Euros or so, and this is quite pricey, on a par with the cheaper stepped attenuator from DACT.
But I'd be confident it would sound good. The relay SA is a very elegant solution, but it's software driven, which introduces a level of complexity not all - especially yours truly - would welcome.
Hugh
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Well maybe that will be in the future but considering the cost of the TKD and Dact, and that I personally like Hugh's M board with the Phono and Sub-Out. So I'm fine for now. One day maybe...
-West