F4 power amplifier

Babowana said:
Again, thanks for the help.
But, the server is blocked here for certain reason I don't know.

I will try to get it from Lee . . .


just sending to ya


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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?



2005-11-08 11:27 am
First stage (complementary JFET pair) is just an input buffer and it's not that critical. Any favourite low current buffer stage with appropriate voltage swing capability can be used.

I think that I would build F4 as na integrated amp, in the same box with Aleph L or Aleph P.
In that case the input JFET pair could be left out of the circuit.

2N4736 should probably be 1N4736 (6.8V 1W Zener)
This one looks fun.

A couple of things please! Thanks in advance.

I remember seeing a reference that the IRFP140 is a better complement to the IRFP9240 than is the IRFP240. Is this true? Would anyone have spare IRFP9240? I have spare IRFP140 I would like to trade off for 9240. :) maybe we could help each other.

Amongst the guys that know jfets - Please don't be shy in suggesting suitable replacements (and hashing out which is best, and why). I am sure more than myself could benefit in how you come to the conclusions you come to.

heatsink on the jfet?

I promised myself no more amps. This one will be the last:rolleyes:

Thanks Nelson!
mpmarino said:
I promised myself no more amps.

Hehehe....I have built ZEN V9 and an F2 lite. Great! Very friendly amps to fullrange speakers. At least I don't need another amp! But...what could be better than a fullranger on the Open Baffle, driven by Zen v9 or F2?
Uhm....you bet-F4 driving big woofers on OB!

But...Yea, no more amps....

Someone on diyaudio once said "Stop pushing my Woo-woo button!"
:D :cool:
I have heard this amp.

Very, very nice amp. It has the JFET sweetness, like the F3, but also has push pull control and is direct coupled. An awesome little amp for those you can live with it's limitations (low gain and low power).

If your system does not work with these limitations consider this amp to be a great excuse to build a better pre-amp and get into high efficiency speakers. Yes, it is that good.