Dual Piezo Wiring with Passive Tone Controls, balance pot and Active pre-amp

Hi everyone,

I am a newb to this site but a long time diy instrument hobbyist with a big interest in electronics. I am currently working on electrifying my banjo and so far I am getting good results that I want to expand on. I've gotten some great info already from the forms here which helped verify some of my own research so I thought starting a forum before I go any further would be a good idea and I reckon this project is fairly applicable to cigar box guitars. I am also thinking to make a cigar box banjo now :)

I will outline my current setup and then pose a few questions:
Two piezo pickups (different types commercially bought, Shadow dual ceramic bridge and Schaller oyster) wired to a balance pot (two outer pins = piezos, center = out) routed to a Shadow piezo 9v pre-amp going to jack. Balance Pot = 25k. The sound is pretty good but when the balance pot is hard left or right it still picks up some of the opposite piezo. I have tried 1M, and 220K pots and gotten better control so I will be trying them again, I think the 220K was better, any thoughts? (- I didn't keep notes so I'll post any new tests and developments once I have my banjo back on the table.)

I need to add a passive bass cut (HPF) to the bridge piezo because it has WAY to much bass. I use an external eq pedal after the preamp to shape the sound before going to a DI box, PA system but I want a permanent low cut on the pickup. My main question is what values should I be looking at for a passive bass cut given that it will go before the balance pot and preamp? I know I could add a 25k tone control after the preamp but I need it right after the piezo and before the balance pot. Should I use active or passive component values? I am now thinking maybe adding the tone after the preamp would be the best way to go.

I have also been getting goods results mixing a magnetic pickup with an external mixer (Boss Line Pedal) and plan to move onto integrating it permanently with the piezo circuit, so more on that soon I hope.

... re: I now think instead of adding a tone control pot I am just going to add a permanent HPF capacitor and resistor after the pre-amp. I need to cut everything under 100HZ or so, maybe up to 2or300HZ. What capacitor and resistor values should I use? Is this probably the best solution instead of trying to make a HPF before the pre-amp? - While I would prefer to have the the bass cut only the bridge piezo the compromise of a master bass cut at the end of the circuit might make the most amount of sense.

.... re,re: The preamp has volume, bass cut/boost and treble cut/boost. Sounds good but even with the bass cut all the way down the bridge pickup is still very bassy. While the external EQ pedal solves the problem I would like to have a permanent bass cut in the circuit so the setup is more "plug and play" on its own.


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This link has a great bit of info on a HPF / bass cut for magnetic pickups.  Would I be correct in thinking this circuit would work after a piezo pre-amp?

I won't have my banjo on the table until next week but I will test all this and post the results.

Reading something some where got me thinking the balance pot could be making the piezos react in a strange way. I have a switch circuit designed that will change from series, parallel and the current "balance wiring". I suspect its almost like the balance wiring makes the pickup act like a capacitor. Its sounds pretty good like this except for the excessive low end.


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