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Old 11th February 2005, 11:41 AM   #1
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Location: Bangalore, India
Default Soundstage with Class A/AB amps

Yesterday I tested with the following setup:

Source: NAD CDP541i
Preamp: Nil
Amplifiers: Rotel RB991, AKSA clone, Anthony Holton's N-Channel, same N-channel with cascode front end & Stochino Amp.
Speakers: Klipsch RF3

Given that Interconnects and Speaker Cables were not swapped, yes, each was a different performer with a different presentation of the music and sound stage; while the Stereophile recommended Class A Rotel was clearly the last in the race, the AKSA and Stochino were neck to neck in almost every aspect - ie., timbral accuracy, low level resolution, dynamics etc., even the width and depth of the soundstage were almost as good as the other; however, the AKSA clone had a very forward soundstage (and hence, sounded more robust and brawny) while the Stochino had a more laid back sound stage and hence, sounded finer and more presentable.

I remember Grey saying something about the "forwardness" of the sound stage with the Alephs at some point.

Any comments or observations?
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Old 13th February 2005, 05:49 PM   #2
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Would someone want to comment about soundstage if finally, with all of its ramifications, that is what Hi-End Audio is all about?
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Old 13th February 2005, 06:29 PM   #3
jcx is offline jcx  United States
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we should give up stereo for the potentially wider and more stable sound stage of 5.1?

- not that 5.1 is really designed to improve this audiophile illusion, nor are quality speakers commonly used esp. center, and the mixing is usually for exagerated effects rather than improved imagng
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Old 13th February 2005, 08:38 PM   #4
AKSA is offline AKSA  Australia
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Samuel,

While your comments on the AKSA are generally flattering, you have either a clone - not sold by me, possibly copied from my intellectual property - or a very early pcb from ESP. With some reservations, I disown this clone because the component choice is necessarily different. Component choice (and layout) makes a marked difference to this design. If it's a copy, did you (or someone else?) copy the Aspen artwork; if so may I ask from whom, and are there other examples of my amplifier 'out there'?

I make my living from this amplifier, various other products, and associated service and my company has never released circuit diagrams, artwork or documentation into the wild. Only paying customers have this information, which is all copyrighted. I am deeply concerned when I hear of clones out there in the 'wild'. Despite its apparent simplicity it took a long time and considerable investment to develop this amplifier, and I would appreciate it if you did not identify it as an AKSA because it is not the genuine product and does not perform the same way.

Of course, it's possible you bought one of the early pcbs from Rod Elliott at ESP. If so, no problem at all; please ignore the above. Otherwise I would appreciate a PM on this if you have the time.......

Cheers,

Hugh
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Old 13th February 2005, 10:38 PM   #5
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Well Hugh, when I think about Pass clones, I try to imagine
myself as Bill Gates, still worried that somebody's running
a pirate copy of Dos 3.0, and it always makes me feel better.

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Old 13th February 2005, 11:11 PM   #6
AKSA is offline AKSA  Australia
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Nelson,

The situation is very different for you, Sir. You are established, published, big marketing setup, you even hold patents.

I see the humor in all this too, but there is a dark side I cannot ignore.

Cheers,

Hugh
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Old 13th February 2005, 11:49 PM   #7
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I, being all too human, have strong feelings about Bill Gates...and they aren't positive.
Okay, lemme see. Soundstage. The comments that Samuel Jayaraj is referring to were in comparison to my tube amps. The Aleph 2s that I built (note the DIY aspect, these are not to be confused with Nelson's commercial product) imaged roughly a foot further forward than my tube amps, perhaps two feet. Meaning that if you were to close your eyes and imagine throwing a wad of paper at a given musician, you would tend to aim a foot or two closer. I traded a few e-mails with Nelson over this at the time and my recollection is that his conclusion was 'it's a mystery.'
My working assumption is that image is rooted primarily in two things: detail retrieval and phase relationships. Since, to my knowledge, no one has ever come up with a way to measure image width or depth, we have to gauge such things subjectively. There are a few truisms that tend to hold, although there are enough counterexamples that you can't state them as absolute rules. One is that tube amps tend to image better than solid state. Why? Who knows? A rabid solid state fan will tell you that tubes image the way they do because of distortion products that create a false sense of spaciousness. My feeling is that such reasoning is spurious at best and may boil down to a simple case of sour grapes. It's curious that these so-called distortion products always sound more like the way real music sounds in a real hall. That said, I've heard tubes that didn't image very well, and solid state that did much better than expected.
The Aleph design sounds very tube-ish for a solid state design. It doesn't sound "like tubes" but it leans strongly in that direction. There are going to be at least two known things involved here. One is that it's a simple design, with only two stages. The other is that it tends towards second harmonic. Comparatively low feedback will probably figure in there as well, although the Alephs still use more feedback than most tube equipment; 20dB NFB (if I recall) vs. about 10-15dB for a lot of the better tube lines.
Parenthetically, note that tube equipment gets pretty good specs for using such low feeback. For some reason, the myth persists that tube stuff has several percent distortion. The truth is that most of the good stuff is well under 1%, and achieves that with very modest feedback. You can get really, really low distortion specs out of tube gear if you're willing to use feedback ratios similar to what solid state uses. Be prepared to build in another gain stage or three in order to build up the open loop gain.
So, does NFB have anything to do with image? It's not an open and shut case. Tube stuff is marvellously forgiving. You can do things with tubes that causes solid state people to cringe, like varying feedback ratios on the fly. Yes, the gain changes, although you can jigger things to offset that if it bothers you. At least between about 6dB and 20dB NFB, there is not an enormous, orders-of-magnitude difference in the image. It changes some, but not as much as you might expect. (It does get brighter tonally, but that's another matter entirely.)
Miscellaneous factoids:
Film caps can improve image for either solid state or tubes, but the basic circuit design has to be capable of decent imaging first.
Fewer gain stages tend to improve imaging.
Lower feedback yields a better image.
Low distortion and imaging are not directly related. This one gets complicated, in that distortion is inescapably related to negative feedback, which does influence imaging. Just don't fall into the trap of assuming that low disortion necessarily means that a purer signal is getting through and hence the image must improve. Ain't so. It's a balancing act. At some point you realize that this falls into the category of voicing an amp and you make compromises.

Grey
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Old 13th February 2005, 11:52 PM   #8
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Hugh,
I see both sides, yours and Nelson's. I have not heard one of your amps. I will not build one even if I happen to come across a known "good" schematic. (I seem to recall that there are various incorrect or obsolete versions floating around on the web.)
Folks, if you want an AKSA, go to Hugh. Please.

Grey
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Old 14th February 2005, 02:08 AM   #9
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My previous post isn't quite as clear as I'd like.
Although I haven't heard one, I have heard enough people say that the AKSA is a good amplifier that I believe it to be the case. My saying that I wouldn't build one should be understood to mean that I would not build an unauthorized copy.
Hugh is one of the good guys. Please support him.

Grey
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Old 14th February 2005, 04:41 AM   #10
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Hugh, thanks for your comments and expressed concerns. My apoligies for referring to the "AKSA clone". This was only to let the forum members know, well, exactly what it is.

This is certainly one of your earlier versions of the AKSA as published by Rod Elliot before it was removed from his site. The thermal tracking is via a pair of diodes rather than the modern version that has a Vbe multiplier. If one were to take that erstwhile schematic and juxtapose it with the one published by Carlos (destroyerx) with your permission, a very close copy of the present AKSA would emerge; yes, only a copy but I am not interested to make gains out of that. As you rightly point out the track layout and component choice do make a difference and in my case, I have chosen both going by what I felt would be best, just to make a comparison.

Given the above, the current version of the AKSA must be fabulous sounding, since what I heard out of 'my copy' was itself the best in terms of both timbral accuracy and capturing the stage nuances. I was only trying to figure out the slight forwardness of the whole sound stage. Thanks again.

Nelson, thank you very much for your comments. You are indeed a happy man; you have a very high degree of security feelings and one of the great reasons for your happy state of affairs is yours blessing the diy community out of your abundance, as much as your commercial success is. You are highly regarded and appreciated.

Grey, thanks for your insightful comments on the relationship between NFB and soundstage. That does throw a lot of light and should provide designers with some guidance while taking into consideration other aspects of circuitry.

Would you say that there is any such thing as a "correctness" to the soundstage in as far as the forward and relatively laid back aspects are concerned?
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