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Old 14th July 2007, 03:50 PM   #1
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Default blameless amp and doug self

New to this site so may be in wrong area so happy to be redirected. Any one have any opinions of Doug Self's power amp? Im thinking of building the trimodal version with a few mods.
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Old 14th July 2007, 08:35 PM   #2
Netlist is offline Netlist  Belgium
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I'm not familiar with this particular amp but try searching the solid state forum. I know the name Self shows up in many threads.
I'll move your topic over there while I'm at it.

/Hugo
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Old 14th July 2007, 09:28 PM   #3
sam9 is offline sam9  United States
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Some of Randy Slone's amps, particularly those with a single LTP and a BJT output appear to be derivative. His "11.4" which refers to the illustration number in his book has been built by several here, including me. The general opinion seems to be positive. On the other hand there have been some unkind words about Self's "blameless"

The Trimodal should not be confused with the "Blameless". My take on the "Blameless" is that it isn't intended to be synonymous with "perfect", "ultimate", "deal" etc but rather a fairly basic design that avoids anything really dumb. He uses it as a baseline for exploring more exotic ideas. The Trimodal is one of those. I've never read of anyone actually building it. There seems to be something of a philosophical chasm between Class A folks and Class B folks. The chasm is filled with much smoke, noise and debate about the definition of Class AB. I suspect the both faction view the Trimodal as an abomination, i.e., a crime against nature.

That said, I think you should go ahead and build. It probably will sound much like his "Load Invariant", which is pretty much what the "11.4" mentioned above is. But keep in mind Self appears to be of the school that believes all good amplifiers used within their capabilities sound alike, and if it should have a unique sound there is something wrong with it.

I think you would generate a lot of interest if you wcould report back here on the results.
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Old 14th July 2007, 10:04 PM   #4
Dave is offline Dave  New Zealand
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Self's book is well worth the read, some of the stuff he points out in the blameless design isn't totally obvious or dumb.
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Old 14th July 2007, 10:31 PM   #5
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I have built the blameless and other derivatives of my own design. It's a great base to work on if you have some tricks up your sleeve; and most of all, a wonderful thing on which to learn the basic theory of multi-stage amplifier concepts.

The results as far as sound goes, in my opinion, are pretty nice with the blameless and my variants. Very clean, high damping factor, fast, and low on the distortion. There can be issues with stability in them if not built or compensated properly, but otherwise, a good layout.

As far as voltage amplifiers go, the blameless concept and its variants are some of my favorites for work-every-time simple amplifiers of high performance. For friends I almost always build something like that if they aren't looking for fancy or expensive.

I do also have a spot in my heart for the world of variable output impedance and transconductance amps, and my adaptations of the blameless design itself were successful in transconductance mode, but sometimes very hard to stabilize how I would like.
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Old 15th July 2007, 05:05 AM   #6
sam9 is offline sam9  United States
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The biggest worry for me in Self's designs (and Slone's) is the CFB output configuration. When it works, its great but they are prone to oscillation. The difficulty is that they are sensitive to the layout of the PCB. With multiple output devices the difficulties increase. If there is set of rules to make is stable I'm unaware. Trail and error seems to be the only approach. This isn't to say one should avoid that configuration but rather not to despair if it the first attempt doesn't quite work as you wish.
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Old 15th July 2007, 06:27 PM   #7
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Yes I have read D Self's books and was very impressed. He does not position himself as an audiophile but as an informed analogue engineer who really understands subtle 2nd and 3rd order effects in the electonics domain. My take is that he makes no claims for the 'sound' only that what comes out is to the maximum extent an amplified version of what went in where THD+N is the measure of imperfection with suitable qualification on the audability of lower versus higher spectral components etc. Given that it looks like a good baseline to work from I will give it a go. There is a company that makes the PCBs. This has been on my 'to do' list for more than a year so may be a while until I get around to it.
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Old 15th July 2007, 08:41 PM   #8
sam9 is offline sam9  United States
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As an aside: I was amused by Self's suggestion the that Class A / Class B switch be labeled Winter/ Summer. I once spent a couple of summer weeks in the Pennine region of Yorkshire. I could have used a nice Class-A amp to drape my soggy clothes over each evening while planning the next day's excursion.

On the other hand, where I now reside it's been 40+C daily for a month and will stay that way until late September so Class is unappealing.
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Old 15th July 2007, 08:43 PM   #9
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Quote:
Originally posted by sam9
Class is unappealing.
Class is always appealing
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Old 15th July 2007, 09:14 PM   #10
sam9 is offline sam9  United States
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I meant Class A, obviously. I'm a good typist, it's my keyboard that is the klutz.
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