F4 power amplifier

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#344
jleaman said:
I might have done all this research and calculations, BUT i don't know the exact information on my heat sink's i guess i could ask some one on here, i just wanted some basic info if they really hot or not, that was all.
Click to expand...


I would agree that Jason is simply too lazy! Besides papa, Steen and I are the only who have said we have built the thing. Whilst steen has no problem with heat in his chassis, I have provided plenty of information on the heat produced by my clone.

Just read this thread and your inbox! For those who doesn't have my comments in their personal inbox, just scroll back 25 posts or so and see what I write.
 
#345
Mr. Pass,

For a DIY montage (100W ouput into 2 ohm load), is it preferable to double the number of pair of Mosfets and size of heatsink or to use the diagram of the page 9 (parallel mono connections).

What is the maximal + - Vcc of PSU admissible by the F4 with the 2SK370/2SJ108 if one increases the size of heatsink and maybe also, increases the number of pairs of Mosfet?

Thank you for your answers

Darry
 
#346
I don't think it is advisable to increase the voltage across the jfet pair too much - they are running close to the specs. If you need larger voltage swing I would recommend running balanced, but with 2ohm speakers I guess you need current more than anything.

You can easily turn up the current if you have suitable heatsinks. If you run single ended mono you should be able to get at voltage swing of +/-20V and with increased bias current, you should be able to get 100W - I think.... :scratch:
 
#347
PMFJI but...

metalman said:
...
Why do I mention all of this, Jason, and why are I and some others at this forum a little harsh with you.
Click to expand...

That was a spectacularly good demonstration of how the lessons of the 1 Minute Manager can be applied to engineering or other technical management. (Even if you haven't read the book, it fits well.)
 
#349
Darry said:
Mr. Pass,

For a DIY montage (100W ouput into 2 ohm load), is it preferable to double the number of pair of Mosfets and size of heatsink or to use the diagram of the page 9 (parallel mono connections).

What is the maximal + - Vcc of PSU admissible by the F4 with the 2SK370/2SJ108 if one increases the size of heatsink and maybe also, increases the number of pairs of Mosfet?
Click to expand...

I paralled the two stereo channels to mono for 100 watts into 2.

There is no margin for extra voltage when using the 2SJ108,
which suffers gate breakdown at 46 volts or so.

I have a modification which I'll publish tomorrow which addresses
this.

😎
 
#350
Why wait - you guys will just start second guessing me in
the meantime.

www.passlabs.com/np/F4R0.pdf

This version bootstraps the front end so that the JFETs only
see about 1/2 the voltage swing. It improves THD very slightly,
gets a tad more output swing, and it also extends the bandwidth
a bit. With a proper setup, I get about -3dB at 1 MHz, with a
very good looking 100 KHz square wave.

😎
 
#354
Great work (like always) Mr Pass 😉

Modifications added - I almost redesigned PCB. I will probably place sources in PDF format for a minute.

schematic f4_r0
 

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#360
This version bootstraps the front end so that the JFETs only see about 1/2 the voltage swing.
Click to expand...

WoW! So are you saying we can get into say +-40v or so, assuming adequate cooling? Where would that put us - 50wpch or so of class A?

Thanks Mr Pass

OH, and before I forget - could you please make any more refinements before I complete mine :clown: because if you do it afterwards I may :bawling: . Not a pretty sight.
 
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