Counerpoint SA100/200 power amp scheme

[Gasho]

I need this scheme , so if anybody have it, please help me.

[shusha]

Here is one.

[anatech]

Here is where the fun starts.

-Chris

[ilimzn]

(Sorry for not posting this in English but the guys are from my neck of the woods )

Iskreno, na vasem mjestu bi se rijesio SA-100 cim prije (citaj: jucer). Tesko mi je naci ma i jedan pozitivan komentar o tom pojacalu, pocevsi od cinjenice da je transformator 2x premalen za snagu koju deklariraju, da napajanje za grijanje redovito spali plocicu i iskuha vlastite filter kondenzatore, da se radi strujnog pika prilikom ukljucenja MOSFET-i mogu sami od sebe spaliti (a vec se odavna ne proizvode), do toga da se jedna od trioda uopce ne korsiti a mogla je linearizirati ulaz. S manje dijelova se moglo napraviti puno bolje pojacalo - ovo sto je sad, bi se najbolje moglo nazvati izoblicilo.
Za poblize podatke ilimznAThotmailDOTcom...

[anatech]

Hi ilimzn,
Can you give us the readers digest version?
-Chris

[Gasho]

Hvala Shusha

Thank´s Shusha.

[ilimzn]

Originally posted by anatech
Hi ilimzn,
Can you give us the readers digest version?
-Chris

Well, more or less what i mentioned about it in the other thread...
I got mine as a fixer, not surprisingly with a cooked transformer. I guess someone decided to believe the hype and try driving electrostatics with it or some other difficult load. Too bad there's nothing subjective about P=V * I * cos(phi) - you can't get 100WPC x 2 from a ~~200VA transformer... never mind that it boasts to be 'dual output' and in fact has the outputs connected together inside the transformer shell, but this amp would not even have to be a perpetuum mobile to stand up to its' specs, but even better: 200% or so efficiency
The filament power supply is downright comical. Whoever designed it has no idea what ripple currents are - placing the series resistor before the rectifier saves both rectifier and capacitors from cooking, and presents a better filter too (and yes, they do cook, and they do not filter overly well either).
Designers obviously also do not believe in regulated power supplies.
They do believe in not using one triode out of the 4 per channel, when the remaining one could have been used in a number of successful ways (active load, for instance), at least for the version i had (obviously different than the one in the schematic, perhaps a lower gain option?). Even the one in the schematic is quite od with regards to feedback, which is DC even though coupling of the stages is AC. Output stage on it's own must contribute some 0.5 - 1% of distortion and it's not the nice kind either. 10N12 and 10P12 are not very complementary...
The whole bias and offset setup starting with it's power supply (limiting the output to about to +-35V or so instead of limiting the gate voltage for all conditions) is odd, to say the least.
Etc etc.
The same parts (or less) could have been used to make a better amp...

[anatech]

Hi ilimzn,
Thanks! Yours sounds like an SA-12 where the follower driving the fets is in parallel (both sections). I can't agree with you more!
Now for the funny part .... the designer says he designs through listening tests! Ears of cloth.

-Chris

[ilimzn]

Well, it did say SA100 on it...
As for listening tests... hm, I'm trying hard to find polite words here.
In the end, I decided to do the following:
I used the high power output of my DAC (this can drive my 600ohm headphones directly at negligible distortion levels) as the input to the SA100, and gave the SA100 a pure non-inductive 8 ohm load. It was tapped at one point to alow me to listen to it through the same headphones at effectively zero amplification, via a switch. The switch cuts in a spare set of the same headphones I have as a load to the point (input or output) that I am not listening to, so that things as much as possible stay the same. I just wanted to be fair, I guess.
Now, the input (= DAC output) sounds the way I am used to hearing whatever it is I am playing. The output of the SA100, with this simplest possible load sounds TOTALLY AND UTTERLY different. You would have to be deaf not to hear that. And no matter how carefully I adjusted it to factory spec, or tried to tweak the bias current. Now, whatever differences you hear this way are entirely artifacts of the amp, and by definition they are distortion. I am sorry if this offends anyone, but to me it sounded just plain WRONG, incredibly inaccurate, and unpleasant.
Since I got it as a fixer, before I even listened to it for the first time, I ended replacing the transformer with 2 transformers, one for the output and one for the tube stage incl heaters, the power output one was a 400VA alone. The mod made the whole amp twice as heavy and barely fit inside, both were on rubber mounts. I also corrected the heater supply. The amp already came with a matched set of E88CC by Telefunken. I also added minor changes to other parts of the power supply (bypassed electrolytics with foil caps).
Listening was such a dissapointing experience I felt sorry for wasting good parts and could not get rid of it fast enough.
The funny thing is, the person who bought it told me that it was the best sounding SA100 he ever heared and he even tested the tubes and found them to be incredibly well matched and probably worth half the price he paid. I really could not take his praise as any kind of a compliment. At one point I was very close to just pulling the whole thing apart and re-doing it from scratch, but I decided it was just not worth it, which is why I sold it.
I still wonder how the manufacturer even sold any at all.
Oh, and BTW mine did not have a primary side fuse at all. It's a wonder it didn't burn a house to the ground when the transformer cooked...

[analog_sa]

Your customer got a deal of a lifetime. Can you imagine what the upgraded transformers would have cost if Designer Mike Elliot had fitted them