F4 power amplifier

[R-K Rønningstad]

Originally posted by Nelson Pass


C3/R25 and C4/R24 are bootstrap networks for the front end.
They slightly improved the maximum output and bandwidth, but
their primary purpose is to protect the JFETs from over-voltage.

R24 and R25?
or ?

[Nelson Pass]

Originally posted by Kashmire
DC servo to null the output DC offset due to potentiometer drift, natural changes during the warmup phase, etc.

Depends on what you want. I get <10 mV after warmup.

[Nelson Pass]

Originally posted by R-K Rønningstad
R24 and R25?

Yes.....

[R-K Rønningstad]

Ahhh! I was looking at http://www.firstwatt.com/downloads/f4_om.pdf.
Could not believe you did not knew your own design .

rkr

[spencer]

Mr. Pass,

I do not have 220uF capacitor handy for C4 and C5 and I am now using a 330uF capacitor. Is that fine? Yes the drift of DC at out put is easily adjusted within 10mV. The drift is mainly on the bias of the mosfet when the amp warms up (from 0.3A till 0.5x A per fet).

Spencer

[Zen Mod]

Originally posted by spencer
..........

I do not have 220uF capacitor handy for C4 and C5 and I am now using a 330uF capacitor. Is that fine? Yes the drift of DC at out put is easily adjusted within 10mV. The drift is mainly on the bias of the mosfet when the amp warms up (from 0.3A till 0.5x A per fet).

Spencer

sometimes even your ( or mine- whatever) fancy schmancy 220uF elco have enough tolerance to approach 330uF in real life ;
accent is on "sometimes" , but that's the fact.
so- why worry........ at least not in that position ............
just use same specimens in sym. positions

[Kashmire]

OK ... thanks guys ... looks like a DC servo is overkill with the F4 topology. Great forum, thanks.

Also, R-K, thanks for answering the C3/R25 and C4/R24 question with a Pass original quote. I appreciate the clarification.

[Gyuri]

Dear RKR!

Look at this:

http://www.passlabs.com/np/f4-power-amp.pdf

Regards:

Gyuri

[R-K Rønningstad]

Originally posted by Gyuri
Dear RKR!

Look at this:

http://www.passlabs.com/np/f4-power-amp.pdf

Regards:

Gyuri

Yes, that was the one I searched out, and made me understand it all.

RK

[Nicola]

Originally posted by cviller


If you had read the thread you would know that "some guy" from Lowther-America has compared them already. It is pointless to keep asking questions already answered in this thread - it is too long already!

Thank you for the comments, I had read the thread, especially this one (http://www.diyaudio.com/forums/showt...12#post1260712), i reckon is the one you refer to, but was hoping to get a bit more from a comparison between the F1 and the F4. Kind regards