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Old 7th August 2003, 06:41 PM   #1
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Default Does Anyone Here Like Class A amps?

Hi everyone!

I would like to humbly ask that everyone please be kind to me as I am new to the forum. Your patience is tremendously appreciated!

I am thinking about building (or modifying) my Project Amp to class A Standards.

I think Class A is for me as I am wanting to absolutely minimize distortion and I am willing to pay for the Electrical Power to do it (I am a BSEET working in the electrical power industry).

We talked about class A amplifiers in college but focused and built primarily class AB and Class D in lab (wether we like it or not the industry revolves around these designs right now). As with any project I begin, I wish to start with research and approach class A Amplifiers as a Novice while learning the particular aspects of this class.

Any class A design that I will commit to build will be solid-state (nothing against our fellow tube fans). I really prefer the more predictable and stable operating characteristics of IC's.

My early research has revealed that there is a tremendous amount of material on the web (more "this is my design" and "what I did's" than theory and application).

So what I sincerely hope is that someone here can help me get to "The Real Good Stuff" so I can develop/select/modify a design and deplete my checking account in the not too distant future and start the building and testing process (I always love how very few people mention the testing part...).

As far as construction I am pretty confident I can handle most designs, but I am looking to start a little higher up the ladder since I have built many electronic circuits in and out of college (PCBs, enclosures, the whole ball of wax!).

I am very much looking forward to this groups suggestions since you are much more versed on this subject than I. Thanks Everyone. Hope to hear some suggestions!
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Old 8th August 2003, 12:48 PM   #2
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Default Re: Does Anyone Here Like Class A amps?

Quote:
Originally posted by johnzimm
Hi everyone!

I think Class A is for me as I am wanting to absolutely minimize distortion and I am willing to pay for the Electrical Power to do it
Here's some places you might want to start:

1 - The 'JLH' amp, a John Linsley Hood design dating back to the mid-60's. There's a topic here:

JLH 10 Watt class A amplifier

and a popular web page at:
http://www.gmweb.btinternet.co.uk
(this wasn't working for me at the time of writing, for some reason)

you can get kits at:
http://users.breathe.com/williamshart/classa.htm


2 - Rod Elliott's 'Death of Zen', which is a very similar architecture to JLH's:

http://sound.westhost.com/project36.htm

the 'Zen' bit is a reference to...

3 - Nelson Pass' Zen series of amps. These are described at:

http://www.passdiy.com/amps.htm

plus of course there's a whole Pass Labs topic on DiyAudio.

4 - The Aleph series of amps, also from Mr. Pass. There's not so much info on these on passdiy, but the Pass Labs topic here is a good place to ask.

5 - The 'Monster' amp by Jean Hiraga. There's a schematic here:
http://www.bonavolta.ch/hobby/fr/audio/monster.htm


6 - You could make yourself a Musical Fidelity A1 clone. There's a useful web page here:

http://www.mhennessy.f9.co.uk/mf_a1/


Personally, I don't have any experience of any of these, but I thought you deserved an answer by now!

If you want my (uninformed) opinion -
(1) and (2) are good, solid designs, and you shouldn't have any problems getting an easy-to-assemble kit.
(3) is more intended as a learning experience, not a genuine attempt at a hi-fi amp. I wouldn't, for instance, want one as my reference amplifier.
(4) is sold commercially as an amp with a good reputation; I'd imagine it's a bit ambitious if this is your first project
(5) is just a bit mad. Car batteries plus every variety of large PSU capacitor thrown in for luck, yet a tiny power output. You might, of course, want something totally mad.
(6) also found fame as a commercial amp; it's unlikely you'll find any kits or PCBs, but it might be simpler than (4).

Relatively low output power goes with the territory, of course.

Cheers
IH
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Old 8th August 2003, 05:24 PM   #3
moe29 is offline moe29  United States
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(3) is more intended as a learning experience, not a genuine
attempt at a hi-fi amp. I wouldn't, for instance, want one as my
reference amplifier.



IH,

for someone who hasn't built a ZEN amp you seem pretty sure
that it isn't HI-FI quality.... hmmmmmm. ok.

I'd say my SOZ is HI-FI, and i actually built one

Zen's are educational though! a nice bonus to go with the nice sound!


moe29
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Old 8th August 2003, 05:40 PM   #4
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Default Re: Does Anyone Here Like Class A amps?

Quote:
Originally posted by johnzimm

I think Class A is for me as I am wanting to absolutely minimize distortion and I am willing to pay for the Electrical Power to do it (I am a BSEET working in the electrical power industry).
If "absolutely minimal distortion" is your goal, I'm not sure that class A is the answer. Many class A designs call for little (or even no) negative feedback, resulting in higher THD numbers. But then, THD isn't everything... I'm no expert, but the consensus seems to be that high amounts of negative feedback are more detrimental to the sound than higher (but still within reason) distortion levels.
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Old 8th August 2003, 06:03 PM   #5
MikeW is offline MikeW  United States
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We love class A amps.
Look in the Pass Labs forum there are plenty to choose from. I haven't built one that sounds bad.
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Old 8th August 2003, 06:34 PM   #6
Netlist is offline Netlist  Belgium
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I've heard a lot of amps in time and must say that the best sounding amp was definitely the AlephX. Sure there will be amps out there with better characteristics.
Take a look at the birth of this nice amp here:
The Aleph-X
Here you will find a very good reference to a 'special version':
This is not just another Aleph
And here is my implementation of this beauty:
Industrial AlephX High Power version

BTW, a warm welcome to the forum.
Keep us informed.

/Hugo
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Old 8th August 2003, 06:53 PM   #7
sam9 is offline sam9  United States
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If absolute distortion numbers are the goal, check the class A design in D. Delf's book (or even his trimodal for which pcbs are available via his website). Randy Slone has one in his amplifier book as well. Both look a lot like their class B designs but biased into Class A. The distortion numbers are ultra low -- few hobiests will have the equipment to verify them.

No - I haven't built them - I live in rather warm climat and don't have AC. I'm not being funny by saying this - I've an aquaintance who uses class A's and I don't know how he stand to use them in the summer months. Self's Trimodal is cute in this regard - you can swith it between class A and B - he labels it Winter and Summer - but he lives on a cold wet island!
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Old 8th August 2003, 09:42 PM   #8
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I have been told THD under 1% is inaudible
and even Mr. Pass has amplifiers rated for 1% THD.
D. Self's book focuses alot on lower distortion perhaps
for technical reasons, because as an engineer it's
the cool thing to do.....not necessarily for audible reasons.

And tube amplifiers are even worse for THD and people love it

What is more noticable is power levels and low powered
amplifiers are typically overdriven by the end user
which causes audible nasties..... if you need 50w, design
for 2x more min. - hehe
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Old 11th August 2003, 11:15 AM   #9
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Quote:
Originally posted by moe29

IH,

for someone who hasn't built a ZEN amp you seem pretty sure
that it isn't HI-FI quality.... hmmmmmm. ok.

As I said, this as my uninformed opinion. I'm paraphrasing threads such as this one:

Zen V4 audio quality

in which NP himself warns that it's "not for everybody".

I wouldn't want somebody to build one with the wrong expectations, and then accuse Nelson of peddling poor designs. Personally, I've got nothing but admiration for someone who's prepared to risk his company's and personal reputation in an open, online forum like this one.

Cheers
IH
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Old 11th August 2003, 11:37 AM   #10
PMA is offline PMA  Europe
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Yes - I like class A amps. But they must be the low distortion ones, not only "simple".
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