F4 power amplifier

[jacco vermeulen]

Originally posted by juma
In that case the input JFET pair could be left out of the circuit.

Without the JFET input it would look like a PP output stage for a hybrid tube-MOSFET power amp, such as the one on the picture.
I've tested that output stage, connected to a pre-amp before the tube front end was hooked up.
Adding a buffer and then running the circuit balanced is a really cool idea. Wish i thought of that, as usual.

[wuffwaff]

Originally posted by flg
There is something a little confusing here though Grey The old Class A peak output current rule... That you can get double the queicent current out. Nelson gets more than that???
Dosen't this thing idle at 1.5A or so??? Gets 20V peak to the load??? O.K. thats good for 25Watts out...
But when you drive a 4 ohm load... If you can drive 20Volts out, thats 50 watts like he says but thats 5A pk??? Well beyond the double the idle current addage of old. Does this thing do Class AB for that power level???
Did I miss something???

Yes,

AB it is.

William

[MRupp]

While the rails are similar, I'm not a big fan of running tubes at reduced voltages.

Yes, but in this case you have a tube designed for low voltage, max. anode voltage for ECC86 is 30V and running them at say 12 V is within their normal operating range. It might not be the best tube for other reasons though ....

[steenoe]

I have a nearly infinite capacity for 'woo.'

Me too I can be woo-woo'ed all day with no ill effect, at all. I think it was Metalman who said the "woo-woo- button" thing
F4; another genious act of Mr. Pass. Did anyone build this thing yet?
Being a study in simplicity, it shouldn't take long to weld one together

Steen

[Nelson Pass]

Originally posted by flg
You mean that bootstrapped TL refrence bissiness???

There's a bootstrap in the amplifier?

Originally posted by wuffwaff
AB it is.

The calculation goes 1.59A * 2 = 3.18A peak

3.18 * 3.18 *8 = 80 watts peak Class A into 8 ohms

and 40 watts peak into 4 ohms

[Zen Mod]

Originally posted by steenoe

Me too I can be woo-woo'ed all day with no ill effect, at all. I think it was Metalman who said the "woo-woo- button" thing
F4; another genious act of Mr. Pass. Did anyone build this thing yet?
Being a study in simplicity, it shouldn't take long to weld one together

Steen

who can be faster than you in this?

hehe
you even have pcb pdfs.........

[steenoe]

you even have pcb pdfs.........

And also even have matched IRFP9240's in the drawer, together with a bunch of Toshiba's

Steen

[Zen Mod]

Originally posted by steenoe

And also even have matched IRFP9240's in the drawer, together with a bunch of Toshiba's

Steen

hehe..........you don't have N and P jfet in one case ..........

[Nelson Pass]

Commenting on the particular mis-match of the complementary
types, notice that the distortion is primarily second harmonic
on the amplifier and that the distortion vs power curve looks
just like a classic single-ended amp.

This imparts a particular sonic signature different from the
usual push-pull arrangement where the character is 3rd harmonic.

[steenoe]

Mr. Pass, that was just, what I needed to hear (read!)

Steen