Best Amplifier?

Xavier

Member
2001-09-07 6:08 am
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".

Thanks
- XL.

[Edited by Xavier on 09-28-2001 at 10:24 PM]
 
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.
 

Xavier

Member
2001-09-07 6:08 am
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.

Thanks
-XL.

Simpson-Can you help me with Neil's GM75 package.
 
Xavier:

"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.

http://users.ece.gatech.edu/~mleach/lowtim/

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.

http://www.sealelectronics.com/supplies/supplies.htm

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.
 

Xavier

Member
2001-09-07 6:08 am
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.

Thanks

- XL
 

wessol

Member
2001-08-14 12:11 am
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.
 

djk

R.I.P
2001-02-04 4:23 am
USA
A friend of mine has four channels of the Leach low TIM amp.It is better sounding than 99.9% of all commercial amplifiers.His have been running for 20 years now.The last 10 years driving a 2 ohm load.They put out 300W per channel at 4 ohms and use three pair of MJ15011/15012 at +/- 63VDC.I was going to upgrade to heavier outputs when he went to 2 ohms but it hasn't been a problem.This guy likes to hammer too.The only serice required has been to replace all the small electrolytics about five years ago(they just dry up and go away).If you want a state of the art project build the Super Leach and add a floating supply. http://www.passlabs.com/images/misc/pat_5343.jpg This will allow you to run class A bias without the heat.I'm sure Nelson Pass won't mind you using his patent.You only have to change a couple of resistors on the Super Leach to do this(and of course the extra supply).It can be retrofitted to a low TIM Leach but will require adding the cascoded output stages.
 

Nelson Pass

The one and only
Paid Member
2001-03-29 12:38 am
I don't think anyone has ever built an amp based on that
patent (which is mine), except of course me, and then only
by way of prototyping. I have tucked it away for some future
use when I run out of new ideas.

Actually, I recommend #4,115,739, Sano et al, as the circuit
you should try. It would be simpler for you to build, and
also works very well.
 

Nelson Pass

The one and only
Paid Member
2001-03-29 12:38 am
Oh, sorry, I forgot that you were asking how it worked:

The idea is simply to get the actual gain devices up to a very
high idle current that doesn't pass through the main supply,
thus increasing the overall efficiency. This extra idle current
comes from constant current sources which are supplied by
an isolated low voltage source.
 
Going back to the original question, I don't think there is a best but all of the options mentioned are good. Which one may depend on your needs. Some of Self's designs for which you can buy PCBs (see link on his site) strike me as exploratory vehicles. I.e., investigating a means to attack one or more particular problems. As a result the Trimodal and Load-Invariant are pretty complex in the sense of high component count. I'm not adverse to that, but it does increase the odds of incorrect assembly.

For example: For me the Trimodal addresses a problem I don't have. On the other hand the Load Invariant is very germain as I have speakers that have low impedance over much of their frequency range.

The straight Blamless design is pretty straight forward and relatively simple. The performance results are good.

The last I heard the only Slone amp for which he still sellsPCBs is the Opt-Mos. This is a fairly complex looking design but from what I've seen of the PCB layout he keeps the part density reasonable. A big plus is that if you run into difficulties Slone will respond to e-mails and walk you through a diagnostic process figure out what went wrong. Other posts here indicate that Self id fairly non-comunicative.

Power may be an issue as I believe the Self designs top out at 100W unless you feel up to making modifications. The Opti-Mos can be configured for rather hgh power levels.
 
I too would reccomend you seriously explore the Pass designs in depth...which won't take much of your time unless you're going to sift through that huge Aleph-X desigh thread with close to 2K posts.

Although I've not built many other amps myself I have owned quite a number of approaching 10K dollar high end amps over the years. So far none of them has even came close to the less is more Nelson Pass concept. My present amps are Aleph 2's...my next one will be a mini Aleph and then a pair of water cooled Aleph 2's with 1KVA toroids in them.

You would be wasting yout time building anything else!!

Mark