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Hi, amateur rewiring nut here.

I've got an Epiphone Les Paul that I'm putting a piezo bridge in. What I've decided to do is make what was the neck volume and tone be a master volume and tone for both of the magnetics and make the other two pots be a magnetic/piezo blend and a tone for the piezo. The master magnetic volume and tone are no problem, obviously I just wired them after the switch instead of before. The piezo blend is likewise no problem, the preamp for the piezo comes with a pot that allows me to mix the preamp's out signal with the magnetic signal just fine.

The problem is the piezo tone. The piezo preamp has no on-board eq at all and was never designed for the inclusion of any eq or tone control. That's supposed to be done outboard but I'd rather not because then any outboard eq is also affecting the magnetics. I'd also rather not wire them in stereo. So I wired a passive-type tone pot to the preamp side of the blend pot (I used 25k pot with a .020 cap). It doesn't work. It has no effect whatsoever on the piezo sound. My question is, is it possible to wire a standard, passive-type tone circuit to the piezo? If so, would I do so before or after the preamp, and what value pot and cap should I use?

For clarity's sake, I've composed the following diagrams in photoshop. Just click the links to see the jpgs.

This is what I did. The blend worked fine, as did the magnetic tone, but the piezo tone didn't work at all. So I can think of two other options to try, but I'd rather not experiment with both if I can help it. Not just because I'm lazy, but for fear of damaging the preamp's delicate circuit board by exposing it to the soldering iron over and over.

Option A. Wiring the piezo to tone before the preamp. I don't know anything about piezo signals, though, so I don't even know if a treble bleed circuit will work. Will a cap bleed off treble in this case?

Option B. Here's another idea I had: if the piezo signal won't bleed off to common ground through a cap, would it bleed off to the lug on the preamp that is designated for the piezo ground/shield? I mean, there has to be a reason why the preamp has a special lug for the piezo ground/shield instead of the directions telling me to just solder the piezo ground/shield straight to a pot's case, right?

So..... what do you recommend? Option A, Option B, or is what I'm trying to do simply not possible? Or did I have it right the first time and simply used the wrong value pot and/or cap?

Any insight you can bring would be greatly appreciated.

[edit]
Oh, by the way, if the first thing I tried should have worked as far as you know, please say so and I'll check my wires for shorts.

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The Prince of Dorkness

hey man did you ever get anywhere with this? I think I might be able to help -- By magnetics you are refering to your guit pups? piezo is the bridge? correct? Also where did the unit come from? bridge and the pre-amp --

Yes and no. I found that a 0.100 microfarad cap works for a tone pot for this preamp in the first wiring setup I tried. However, after getting it to work I found that the preamp, battery, and all the wires didn't fit well in the control cavity due to every pot but one being push/pull. After much thought, I decided that versatility from the magnetic pups through the push/pull pots was more important to me than the piezo. Probably I'll re-install the piezo bridge when I have the cash to spare to have someone rout a battery compartment into the body.

[Edit]
Oh, by the way, in answer to your question this is the L.R. Baggs X-Bridge piezo tune-o-matic style bridge with the L.R. Baggs Control X preamp. If you're thinking of putting a piezo bridge in a Les Paul style guitar, though, I strongly recommend you use the Fishman piezo bridge and preamp instead. The L.R. Baggs preamp is made specifically for Strats and therefore the pot is just barely tall enough to get through the top of the LP, and you lose the mono/stereo switch unless you either drill a hole in the top of your LP or rewire the mono/stereo switch to a push/pull.

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The Prince of Dorkness

well cool I am glad you got somewhere with it -- I am curious though -- What exactly is benifit or use of the piezo bridges? Just another tone? I have never played one --

A piezo transducer is the method by which most acoustic/electric guitars, such as this one, are able to be run through an amp or PA system. A guitar bridge with built-in piezo transducers under the saddles, like this one, allow an electric guitar to sound like an acoustic guitar when you want it to.

Note that for this mod you would have to drill a hole in the top of your guitar under the bridge for the wires. Not something most people will want to do unless the guitar in question isn't very valuable. Also, if your pickups are clean-sounding like most stock pickups, then there's not a whole lot of point to doing this. If you have grittier sounding pups like Gibson Dirty Fingers or Burstbuckers, then it may be worth it.

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The Prince of Dorkness