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Old 29th September 2001, 03:15 AM   #1
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Guys, it may sound insane but I have been trying to build an amplifier which would really worth my time and money, for every step I move ahead, there comes a problem which pushes me a furlong back, therefore I came here for your valuable help.

My first choice was Load Invariant Amp by D.Self, but now I have ruled out that option and trying with the other design of his( Blameless Class-B or Trimodal Amplifier). I feel not many of them had built these amps, but I welcome your precious information about these amps if u have over heard any.

I'm kind a biased towards Self'd design, but I also welcome your comments about any other amplifier which might have excellent THD, Bandwidth, solid reliability etc..

I'm looking for an amp in the range of 120W-200Wrms. I'm also looking for the articles publised by Self on "Muting Relays".

- XL.

[Edited by Xavier on 09-28-2001 at 10:24 PM]
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Old 29th September 2001, 04:45 AM   #2
hifiZen is offline hifiZen  Canada
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Well, Douglas Self does make very thorough investigations into amp design, and does an excellent job backing them up. A good read of his series on power amp distortion in EW&WW should be a required read for every amp designer (shame on his critics who havn't read and fairly evaluated his words), whether they agree with his philosophies or not. There is much more to be gained from his papers than just his point of view. However, in the years since I first read these articles, I've come to understand that Mr. Self is not the ultimate authority on power amp design. Really, I don't think anyone is. Mr. Self tends to focus strictly on traditional measurements which I feel are not entirely adequate to explain the subjective qualities of solid-state amplifiers. Doug also likes to dismiss subjectivists as irrational, simply ignoring the fact that the subjective opinions of many audiophiles may actually have undiscovered scientific explanations.

Several years ago, I built an amp based pretty much directly off of Mr. Self's designs... the GM75 by Neil McGann. Neil's website is no longer on the net, though I have mirrored the whole thing on my own website. Unfortunately, my site is currently without a home, but I hope to fix that soon. In any case, the GM75 was one of my early projects, and Neil's site had superb documentation on his design. This was one of the reasons I chose to build it. As far as sound quality goes, it is excellent, but not the best I've heard. It is currently the amp I use most.

There is another set of Self-style designs done by Randy Sloan, which might be the ticket for you. Look for his book, "High-Power Audio Amplifier Construction Manual". This book presents some nice designs, but is basically a verbatim regurgitation (interspersed with some highly opinionated statements) of Doug Self's EW&WW articles, which are much more detailed and thorough. So, I suggest you not bother with the book, and instead read straight from the source articles in EW&WW. The only thing you might get from the book which is not covered in Doug's articles is an overview of some output protection circuits. Sloan has a website and sells some parts I think. It's called Seal Electronics or something.

Anyway, if you agree with Doug's philosophy, you should find that building one of his designs or derivatives thereof will be well worth your time and money. The GM75 has been a very solid amp, and it's MOSFET outputs have some agreeable benefits over the bipolar outputs Self typically employs (Doug doesn't seem to like FETs). If you're interested in the GM75 design, I can package up the entire HTML archive of Neil's website and send it to you...

I'll also have a peek and see if I can't find which EWWW issue contains the Muting Relays article.
- Chad.
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Old 29th September 2001, 05:47 AM   #3
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Simpson, thank you for your post. My idea about amplifiers had so far been the same, which is; any amplifier that is transparent and can faithfully reproduce sound at it output without ANY(far less) distrotion is the one. Keeping this in mind and searching for an amplifier made me read two books, one by Douglas Self and the other by Randy Slone.
Though Slone follows Self's thoughts, Slone focus is on mirror-image topology which might absolutely increase slew-rate and PSRR. As like any other DIY hobbyist I kept pondering over those design every night until I finalised a design by Slone. Then I called him and was surprised to hear that the design(OPTI-MOS) he had publised on the web is way and far better than all of his text book design which again put me form where I started. Therefore I continued with Self's book then joined this forum and now I don't know what design to choose for there are many here.

Every person's view in matter how an amplifier should sound, preceived and heard is high individualistic.
Reading through all posted threads I found out that nobody had said that "this is The Best Amplifier" I have built or listened to. I know that "mind" always saying that the neighbour's amplifier is sounding better.

All I want is an amplifier that has very less distortion, excellent bandwith, slew rate, PSSR and high reliability.
Is OPTI-MOS a good choice? I welcome your commnets and opinions.


Simpson-Can you help me with Neil's GM75 package.
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Old 29th September 2001, 09:12 AM   #4
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Where can I find the OPTI-MOS design?


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Old 29th September 2001, 02:36 PM   #5
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Default opti-mos
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Old 29th September 2001, 04:52 PM   #6
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Sam, pmkap is right, may be u can even try his book "High Power Audio Construction Manual". Many cookbook designs there.

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Old 29th September 2001, 07:18 PM   #7
Super is offline Super  United States
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You can always try a Pass Labs design...

I don't think there's a person on this forum who has built one and been displeased. And in terms of troubleshooting, if the typical members can't help, well, you can always ask Mr. Pass himself, who's a frequent visitor here! Good luck.
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Old 29th September 2001, 09:06 PM   #8
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"Best" is a very difficult quality to define in amplifier design.

I tend to prefer Self's and Sloan's designs and opinions,
and think you can build very good amplifiers based on their designs. At present I prefer to work with bipolar transistors rather than MOSFETs, and Class A amplifiers are
simply impractical for my needs.

Try also looking at Marshall Leach's design; it is a nearly perfect mirror-image topology with a high PSRR and eschews active current sources and mirrors--some people tend to prefer the sound of resistive current sources. I've built
and used his designs for the last couple of decades with
very good results. I'm presently updating my amplifer to
his current version 4.5 boards; his design has changed little over the years but I wanted to incorporate all of the design refinements.

Otherwise I'd recommend biting the high-current bullet and building one of Nelson Pass's Class A MOSFET amps; Class A
should have the lowest possible distortion, but the high
power dissipation is a severe drawback for me.

All three designers offer sources for circuit boards; Sloan has many of the semiconductors, transformers, heatsinks and capacitors you'll need.

I've recycled parts from earlier projects into a new/old amplifier and intend to use it as a test bed for some circuit ideas I want to try out. Among these are a complementary-feedback output stage (aka Sziklai), and using
2SA1302/2SC3281 power transistors in place of MJ1500x devices as these are more linear over a wider current range.
Since the worst distortion offender is the output stage, I focus my present thinking there.

There is a danish design that is similar to the above design topologies but does not use global negative feedback--at all. Zero. Zilch. I have no idea of the quality, and
don't have a URL handy at the moment, but I >think< they do offer a circuit board.
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Old 30th September 2001, 02:26 AM   #9
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Thank You Damon. I have browsed through Leech's amp, but most of my time had been spent with staring at Self's design, so I'm going ahead with his Load Invariant or Class B design. For time being I'm not considering building any Class A or amplifiers that incorporate mosfet output stages, therefore I have looked nothing beyond though Pass Amps is being popular among DIY hobbyist.

Speaker impedence is a variable, therefore Load Invariant will provide better distortion even when the impedence dips to 4 ohms.


- XL
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Old 30th September 2001, 02:38 AM   #10
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I have built 6 of the opti-mos amps, 4 of the 200 watt versions and 2 of the 400 watt versions, and am very pleased with the sound quality, and the time Randy Slone has taken to answer all my questions about his amps and anything else.
If you have any questions I am sure he would be more then happy to answer them.
If you want to piece one of his amps together he is willing to sell you the whole kit or any parts of the amp kit individually.
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