F4 power amplifier

[Dougie085]

I tried reading through this to find out but can't seem to find a spot where it says. Are there PCB's available for the F4? I'm very interested in it for sure. But I don't have the skill nore the space/materials to etch my own board.

[mpmarino]

A search on the words "f4 pcb" currently yields this .

[korben69]

BOM fixed.
The mistake was concerning R3 and R4 : 22.1R - R8 : 22.1K
C5 - C6 caps are optional, printed on Peter DANIEL PCB for PS filtering.
According to Mr Nelson PASS User Manual r0 - 4/17/07.
Many thanks to you Mr PASS !
Value for LED is supposed to be thrue... maybe someone to confirm ?

[nonoise]

Question
According to Fairchild's cross reverence engine
The following fet's are equivalent to the standard IR parts

IRFP9240 = FQA12P20
IRFP240 = FQA19N20C

There are two reasons for the question
Somewhere on the forum some one sed that Nelson actually uses the Fairchild part’s

The Fairchild parts are much cheaper via my local distributor

[pchw]

Originally posted by korben69
BOM fixed.
The mistake was concerning R3 and R4 : 22.1R - R8 : 22.1K
C5 - C6 caps are optional, printed on Peter DANIEL PCB for PS filtering.
According to Mr Nelson PASS User Manual r0 - 4/17/07.
Many thanks to you Mr PASS !
Value for LED is supposed to be thrue... maybe someone to confirm ?

There is one more typo. Q11 should be TL431.
Thank you for maintaining the BOM, and of course, Nelson and many others, too.

[korben69]

You're right pchw, Q11 is TL431 from Ti.
My BOM refers to Peter DANIEL PCB boards, TL431 is masked as Q11.
This is the right value in this case.

[R-K Rønningstad]

Originally posted by GRollins
In an attempt to short circuit the inevitable questions:
--Yes, you can increase the bias as long as you have sufficient heat sinking/power supply/etc.
--Yes, you can decrease the bias.
--Yes, you can substitute the usual MOSFETs for the IRF outputs.
--Yes, you can substitute the input JFETs, but the field of candidates is much more limited.
--I don't have the datasheets for the input JFETs with me at the moment, but I don't think you're going to want to increase the rail voltage much. The outputs can take it, but the inputs can't. If someone knows where to find 100V low noise, complementary JFETs with reasonable current capability, I'm all ears.
--Yes, you can decrease the number of output MOSFETs, but watch the heat dissipation per device.
--Yes, you can increase the number of output MOSFETs, but bandwidth and distortion will suffer as a result--though not fatally.
What'd I miss?

Grey

Hey, the F4 is a great concept. You could of course increase the rail voltage, in principle run it in class B or G or whatever. But as it is basically an emitter-follower (source-follower, OK then) it has gain of slightly less than one. So it would need a large-swing preamplifier to be of any use (with high rail voltages).
This means simplifying circuitry, really. One may say that the traditional input stage of the power amplifier is moved to the preamplifier. In other words less cascading of gain stages.
With a preamplfier able to swing +/-40 Volts you will get quite some wattage out from an emitter-follower. :-) Yes, 100W in 8 ohms.
BTW, all this might be said in the tread somewhere, but I just could not read through all 93 pages after Nelson's original post, so please excuse me for just dropping in like this.
Anyway, nice thinking, NP.

Rolv-Karsten

[Nelson Pass]

Originally posted by R-K Rønningstad
Anyway, nice thinking, NP.

Of course the concept's been around.

Hardly anybody has tried it, though.

[R-K Rønningstad]

One could use the concept to increase the current capacity of whimpy 100W or 200W power amps, so the whimpy one could provide the - hopefully - clean voltage - and the huge follower could provide the muscle. I MUST have heard about a similar philosphy many moons ago... somewhere.... ;-)

[Zen Mod]

old booster amps from toob era.......... for theaters ,but later also for cutters ..............even if they mostly have some gain..........