Aleph AC current gain made easy

[darian]

Hello,

I always wanted to know how to predict the value of the AC gain in an Aleph according to the current source "feedback" resistors (R12 and R15 in the attached image for example). I couldn't find it anywhere on this forum so I finally decided to do it myself the old way on a piece of paper with a pen. It was worth because I understood the quite tricky behavior of the aleph current source which responds to the modulation of the lower mosfets by a sum of positive and negative feedback (yes, I said positive) the later being of course stronger.

I wanted to share with you for comments and to help the people not having an oscilloscope and a sinewave source at home (many people I guess).
My calculation is assuming the output resistance (R20 and 21in parallel in my example) is half the one of the current-source source resistor in parallel (R18 only here) which is the usual topology. It works whatever the number of fets is if this condition is respected.

We will call : B=R12/R15 (so it’s less or equal to 1)
and : A=AC gain

B = 1 / (2xA)

For information :

Imax = Ibias x 2B/(2B-1) = Ibias / (1-A)

but it was already available in the Aleph power xls file.

I hope you will find it useful : I think it’s always better to have a real resistor instead of a trimpot. You just pick your value (or values you can choose from with a jumper) and go… no more trial and error for that!

I think I made no mistakes... Waiting for your comments people...

Bye

[darian]

I see my post is not interesting to many people! Not even one answer... Next time I'll think twice before posting... If there is a next time...

[Zen Mod]

Originally posted by darian
I see my post is not interesting to many people! Not even one answer... Next time I'll think twice before posting... If there is a next time...

don't be so peakey


ppl sometimes do not answer when they have nothing to complain.......


tnx for effort, in any case

and- keep posting

[Nelson Pass]

Originally posted by Zen Mod
ppl sometimes do not answer when they have nothing to complain.......

That's right. Sometimes we have to do triage to keep up.

If you email me and don't get a reply right away, it probably
means that your problem had no dangling eyeballs involved.

You should be complimented that nobody found any errors.

[sprintsun]

Mr Nelson Pass,
Sorry to interrupt, does it mean that my aleph 4 in aleph4 basic question is ok?

[sprintsun]

Mr Nelson Pass,
Sorry to interrupt you again, the aleph 4 sound so good, why do you retire such a good amp?

Don't tell me it's for "us who can't afford to diy".

It would be so generous of you, Mr Nelson Pass. Like you say, "The one and only".

[Nelson Pass]

Originally posted by sprintsun
does it mean that my aleph 4 in aleph4 basic question is ok?

Does what mean your Aleph 4 is OK?

Originally posted by sprintsun
why do you retire such a good amp?

Actually I don't say "the one and only", that sobriquet was
bestowed upon me by administration.

All good amps retire. Design moves on.

[sprintsun]

Does what mean your Aleph 4 is OK?

Embarrassed, I was refering to this concernng non reply on Aleph 4 basic question from your goodself:

If you email me and don't get a reply right away, it probably means that your problem had no dangling eyeballs involved.

[Nelson Pass]

Ah yes, thank you.

I'd better get back to my email pile.