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FDP Forum / Guitar Mods, Repairs, and Projects / Volume and tone control on a piezo preamp

Contributing Member

New Jersey

I'm back with the otters again
May 20th, 2017 04:57 PM   Edit   Profile   Print Topic   Search Topic

I'm looking at a very simple jfet preamp that seems to be a popular design but no one seems to ask the question on this website about a volume control or maybe a tone control. The source lead of the jfet goes thru a 10K resistor to the output. I'm thinking that a pair of 250K pots (volume and tone) should be fine. Its a little bit more than 10 times the output resistor but I don't know anything about active circuits.

Contributing Member

I've got my own

double-cross to bear
May 21st, 2017 08:37 AM   Edit   Profile   Print Topic   Search Topic

This looks like a pretty good one that will conserve battery power too.

2-stage JFET pre schematic

Contributing Member

Paris, France

It's just a guitar, not rocket science.
May 21st, 2017 09:07 AM   Edit   Profile   Print Topic   Search Topic

I don't know enough about these things to answer with anything resembling confidence but I wonder if adding 250kΩ to the back end of the circuit will mess up the jfet bias or somesuch whatnots. 250kΩ seems too high. For magnetic pickups, fine, but not an active circuit. Volume pedals for example, typically use 250k pots for passive guitars, and 25k pots for active circuits.

FDP Forum / Guitar Mods, Repairs, and Projects / Volume and tone control on a piezo preamp

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