My AB amp inspired by AlephX

[DarkOne]

Hello,
I allways loved class A amps, but it's allways problem to get all heatsinks needed (mostly because their high price), so I designed my amp like alephx which can work in class AB. Both output halves are biased to 1A, which can drive my 8 ohm speakers 20Wrms in class A, but circuit is able to run more power in class AB. I know I made some sins like complementary differential input stage etc. But the question is - what do you think about it and what would you make other way?

The amp is running for 4 months and I'm very satisfied with results (sorry no measurements). I'm going to integrate 4 chanels to one chassis and use active crossover for my speakers.

Attached schematic is very simplified so here are some details : for thermal stability I change current biasing diff pairs (this sulution took me some time to develop, but works and it's simple). Source resistors on output pairs (IRFP240 & IRFP9240) are 0R47 and currently I have 16 output transistors per chanel. In my future project (4 chanels) I'd like to run only 4 devices (minimum for this circuit) per chanel.

So, what do you think?

[Nelson Pass]

Looks great. Congratulations.

[DarkOne]

Thanks Mr. Pass

[B.L.]

Actual schematic please.


No problems with DC offset?

[DarkOne]

No problems with DC, as can be seen on actual schematic, there are 4 resistors from both outputs to each CCS (like in AlephX). Currently I have 30mV between outputs and 150mV to ground.

[LBHajdu]

It’s a very nice amp and truly simple ! Could you comment on the sound (maybe a comparison to something else)? What rail voltage are you running them at? If others want to try building it you should post the component values.

[DarkOne]

It's hard for me to compare, because I haven't had opportunity to compare to other amps on the same gear. Currently I have Canton LE103 speakers, which I heard playing on Krell amp, but there was different source, than I have, so hard to tell. Within few months I'll compare amp on Dynaudio BM6 with Meridian (there will be a pair of golden ears with me, so we'll see).
According to my ears the amp has very smooth sound, L/R localization is perfect, F/R localisation can't check, speakers are not so good and currently I don't have good source. Bass is strong and well controled.

Rail voltages are +-25V with 180mF capacitance

Send me an email for component values (I have them only in Eagle pcb format)

toudy@chello.sk

[Zen Mod]

Originally posted by DarkOne
It's hard for me to compare, because I haven't had opportunity to compare to other amps on the same gear. Currently I have Canton LE103 speakers, which I heard playing on Krell amp, but there was different source, than I have, so hard to tell. Within few months I'll compare amp on Dynaudio BM6 with Meridian (there will be a pair of golden ears with me, so we'll see).
According to my ears the amp has very smooth sound, L/R localization is perfect, F/R localisation can't check, speakers are not so good and currently I don't have good source. Bass is strong and well controled.

Rail voltages are +-25V with 180mF capacitance

Send me an email for component values (I have them only in Eagle pcb format)

toudy@chello.sk

if you send me that files I can put it on my web for (temp) download if someone else is interested...

[LBHajdu]

That’s very interesting, I’ve never heard of a class A\B push pull amp describe as “very smooth”. I wonder if it’s distortion from the output stage. Is there a high end roll off?

How is the noise floor, is there any hum? This is the Achilles heal of common source operation as you know. However the symmetry must help out some what.

I also wonder if that is why Mr. Pass didn’t use this topology in his amps.

[LBHajdu]

Here is another option, taken from half of a Pass A75 and Xed. But it may have too many stages to make the x concept work. The P.S. rejection will be better.

I’m really ashamed of this drawing. I think I put about ten min. it to it.