F5 power amplifier

[zinsula]

Originally posted by Babowana
The cross line does not exchange any signal voltage between the
left and the right. The reason is that the cross line is an potetial
zero point which is always the centre of vertically symmery in any
case with respect to the electrical potential. Just a thinking . . .

Not exactly.... voltage will sit at zero if the Idss of all JFETs is equal, otherwise it will be anywhere close zero. So far, you are right.

But this isn't important to the function.

Important is the current which flows from one half to the other wîth the signal. This current will change the voltage over R7/8/13/14.
In the F5, this current flows to ground, and here it flows to the other half of the circuit.

It is a diff pair....you have to connect the sources/emitters

Tino

[Nelson Pass]

Originally posted by zinsula
Conceptually, this should work, even if there is no balanced source (pre) available.
"Current Feedback" to the sources of J-Fets, as the F5. Don't know if it would count as X-ed in this case.

Anyone to comment?

Deriving the "voltage feedback" solution (as per susy patent, to the gates) will be trivial for you a-Pass-ionados.

Ciao, Tino

With some value adjustments, this will presumably work, but it is
not an X topology.

[Nicola]

Mr Pass. Sorry to read you hurt yourself in weightlifting x serie. Hope you're recovering well. Thanks for the new F amp, neat design in it simplicity. Single question will FirstWatt build it or will there the opportunity for a PCB group buy ? Regards

[TimS]

Here is a design that I have worked over a year ago, the main difference between this and a balanced F5 is the input mosfets and the biasing circuitry.

I have tried JFETs in the simulation but i can not seem to get the same gain as a mosfet (so higher distortion) and the source impedance is not as low (so lower bandwidth). But then I didn't try the 2SK370 and 2SJ108.

Cheers

Tim

[chrismercurio]

what is the supply voltage? Is it similar to the F4 or wildly diferent?

Thanks,

C

[SCD]

The schematic that Nelson posted lists the voltage as +, - 24Vdc

[Variac]

Don't all First Watt Amps have variations on the same power supply?

[tms0425]

Lots of 18vac transformers

[Zen Mod]

Originally posted by tms0425
Lots of 18vac transformers

yup;

seems that greedy boyz at BAF didn't take them all .....

[chrismercurio]

I was thinking it might be economical to build the PS into a seperate enclosure and tap off of it Naim Style for the various Fx amplifiers.

What do you guys think? Is a possible, relevant, and viable option? More interested in the last 2 options as most things are possible.

C

p.s. I didn't take any traffos. Old Threshold knobs though, and awesome heatsinks!