P channel jfet preamp circuit

[audionut]

Gentlemen

this is a JFET n channel pre amp circuit...

Lets say I want to change it to a P channel JFET pre amp circuit. how would I do that...reverse polarity and swap resistor r3 and r2??

[lineup]

yes.
Basically I think you do right with that.
(even if I can see no circuit)

[AndrewT]

Without seeing a schematic, I think a safer rule would be to swap the polarity of the power feed and swap all semiconductors to opposite type. eg N to P, pnp to npn, diode/zener diode pointing up to diode pointing down, etc.

No resistors need changing, except that the semiconductor parameters may be sufficiently different that requires a small change in resistor value to bring the circuit back to design currents/voltages.

[audionut]

Here's the schematic for the n channel JFET pre amp. to change to P channel...reverse the polarity and...

Swap resistors r3 and r2? or no?...Where does C1 go?

thanx for your replys

[AndrewT]

swap the power feed polarity.
swap to a Pchannel jFET.
swap the two Zeners around (they end up looking exactly the same.
Swap the direction of C" (the polarised cap must be inserted to suit the reversed polarity.
job done.

Do NOT move or change any other components.

I do hope that C1 is chosen for sound quality vs budget.

[SY]

You don't have to swap the Zeners around.

[AndrewT]

swap the two Zeners around (they end up looking exactly the same)

Originally Posted by SY

You don't have to swap the Zeners around.

That's what I said, but the "rule" is to swap all semiconductors. Far easier if there are no exceptions to be listed nor remembered.

[audionut]

Thank you all....I bought some 2sj74 jfets and put them into aleph j boards...firing up circuit, the mosfets bias up correctly but no gain...so I am wondering about the 2sj74's and if they are genuine...I will put one in the pre amp circuit and see it provides some gain in that circuit...if it does, then I have an error in the aleph j build...

[Josip_Del]

Can we do the same thing with front end of BA2 power amp?

[lineup]

Originally Posted by audionut

Thank you all....I bought some 2sj74 jfets and put them into aleph j boards...firing up circuit, the mosfets bias up correctly but no gain...so I am wondering about the 2sj74's and if they are genuine...I will put one in the pre amp circuit and see it provides some gain in that circuit...if it does, then I have an error in the aleph j build...

You probably have an error in Aleph J setup.
Check the circuit around those 2SJ74 - feedback resistors ....