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Test Electrix 21st January 2011 03:08 PM

Guidelines for switching N-channel JFETs to P-channel JFETs (and vica versa)?
Couldn't find anything in the search so I though I'd ask in a thread: I'm wanting to use a P-chan. JFET instead of a N-chan. JFET as I'm trying to incorporate bits and pieces with different grounding for what the original diagram says, what would be the best way of going about working out and implementing this?

DF96 21st January 2011 03:26 PM

Just turn the whole circuit upside down?

Test Electrix 21st January 2011 06:41 PM

So everything in line with the drain is now attached to the source and vica versa?

alexcp 22nd January 2011 07:24 AM

No, that is not what DF96 refers to. Better get an N-channel JFET as specified in the schematic; otherwise, your schematic is likely to end up not working.

AndrewT 22nd January 2011 09:39 AM


Originally Posted by DF96 (
Just turn the whole circuit upside down?

means turn the schematic top to bottom.
Re-label the +ve supply which is at the bottom as a -ve supply.
Swap all transistors for their sisters, i.e. Nch becomes Pch NPN becomes PNP, Pch becomes Nch, PNP becomes NPN.
check and re-orient all polar semiconductors, eg. diodes, zeners, leds etc.

But since you misunderstood the first instruction then I too am inclined to agree with Alex. Don't.

Swap your Pch jFETs to Nch jFETs, you might negotiate 50 to 100% extra devices.
Or hold your stock and wait till a circuit that needs both Nch & Pch jFETs appeals to you.

DF96 22nd January 2011 01:04 PM

Electrolytics too.

Alternatively, if the JFET is being used as a gate or variable resistor it might be possible to just invert part of the circuit. To do this successfully you would have sufficient knowledge that you probably would not have needed to ask the question.

Test Electrix 22nd January 2011 01:23 PM

Haha it's not amazingly complicated and I think it can be done for one particular thing I'm trying to do, this is the schematic:

AndrewT 22nd January 2011 01:38 PM

that is an indicator to tell the operator that "effects" is switched ON.
It does not handle audio signal.

Test Electrix 22nd January 2011 05:35 PM

Of course but the ground is positive for what I'm trying to incorporate it in to, I take it that I don't just copy that circuit with but with the polarities reversed?

Test Electrix 24th January 2011 06:22 PM

I'll just fiddle with it in a circuit simulator and post the results...

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