I have a few questions about piezo pickups with an active (9V battery) preamp. In a large body cbg, I’m thinking of installing a system with 2 piezo discs (or perhaps one under saddle piezo rod and one disc) wired in parallel to a blend pot (either mn250K or mn500k) and then to a 9V battery-powered active preamp with either two (1v 1t) or three (1v 1bass 1treble) volume and tone pot knobs. Here are my questions: (1) What value volume and tone pots do you use with a piezo/active system? 25K? 50K? 100k? (2) Have you ever installed an active preamp with piezo discs, or only with piezo rods? On a related note, ave you ever mixed rods and discs through an active preamp?

I realize I could skip the blend pot and use two volume pots, but that’s not my question, as I want to try with a blend pot. My main question is about pot values in a 9V active preamp piezo system.

For clarity, I’m going to build something similar to this item on eBay, except for a cbg instead of for a bass guitar: https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.com%...

Thanks for sharing your experience!

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Strangely, I don't think the value really matters since the pot will be used for blending.

What power doesn't come from one piezo will come from the other, so in essence it should balance itself.

Sorry, to clarify, I’m not asking about the value of the blend pot. I know I’ll use either an my 250K or mn500K for that. I’m asking about the pot values for the volume, bass, and treble knobs. See this picture of a commercial version of what I’m talking about. That’s what I want to build, except I want to build it for a cbg, whereas the one in the pic is for a bass guitar. https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.com%...

With the preamp, you don't need separate volume/treble... the preamp does all that for you...

Given the high impedance of the piezo, I'd guess a larger value for the blend pot might be better, but Francois is probably right...   Truthfully, Piezo Rod is great, I don't see any advantage to adding a disc, unless you like handling sounds and feedback...

Hi. Thanks, but I am not talking about one of those big black preamp/equalizer units with EQ switches built in that we often see in acoustic-electric guitars. I’m talking about wiring one with knobs (aside from the blend pot, there probably will be 3 control knobs: a volume, a bass control, and a treble control). Also, I’m not actually asking asking about the value of the blend pot. I’m asking about the pot values for the other control pots, all of which will be knobs. See this picture of a commercial version of what I’m talking about. That’s what I want to build, except I want to build it for a cbg, whereas the one in the pic is for a bass guitar. https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.com%...
One other note: Even though I am using piezo pickups, the system will not be high impedance, because it is a powered, active system. Thus, the pot values will be very different from what they would be if I were wiring a passive system that uses either piezos or magnetic pickups.

just make sure the blend pot is a linear pot and NOT an audio taper (log) pot. otherwise it will be difficult to get a blend you like..

Wise words.

The round piezo and rod piezo have different outputs(round piezo is louder and more likely to pick up all handling noise). If your using a preamp from Gitty, I believe these have only one input. This would require the parallel hookup making one louder than the other. 

So a blend pot between the round piezo and preamp input would work. You could use a standard volume pot and wire it: piezo signal to lug 1 of pot, lug 2 of pot to preamp and lug 3 of pot to ground. That will work as a blend.

As for the value of the pot: I would try a 500k first.

I obviously must not have asked my question very clearly, because everyone is responding about the blend pot value. I didn’t mean to be asking about the value of the blend pot. I’m asking about the pot values for the volume, bass, and treble knobs. Also, I’m not using an out of the box preamp that you plug into, from Cbgitty or elsewhere. I’m building one similar to the one you can see in this EBay pic, except that I want to build it for a cbg instead of for a bass guitar. That’s why I need to know the proper pot value for the control pots. Also, even though I am using piezo, the system will not be high impedance, because it is an active, powered system. Thus, the pot values will be very different from what they would be if I were wiring a passive system that uses either piezos or passive magnetic pickups. https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.com%...
By the way, although I was not asking about the value of the blend pot, I agree that I’ll go with the higher value 500K blend pot, since the blend pot will be located between the piezo pickups and the onboard active preamp. The other pots, however, will not be located before the preamp, per the design in the eBay picture I attached.

I got that you weren't asking about the value of the pot to be used at that point, I listed it because of the impedance coming from that piezo being higher, the 500k would help to minimize that issue.

The pots for the preamp system are hard to determine without seeing a schematic. Stewmac and other places might recommend 25k pots for Battery operated preamp systems, but they are usually for EMG style pickups with built in preamps. The preamp your talking about could use a 1k, 10k or 25k pot or a mixture of values. So a schematic would be helpful.

While this article is primarily about pots in passive systems, from the one line about active (powered) systems, it LOOKS like I would need 25K pots. Does that seem right?
https://www.stewmac.com/How-To/Online_Resources/Learn_About_Guitar_...

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