Building an FET Buffer/Preamp for Piezo Equipped Guitars

By Paul Marossy

Last Updated 12/31/05

One day, I was looking for some info on how piezo pickups work and somehow I stumbled upon
this page. I hadn't really thought about my acoustic-electric needing a buffer in front of it since it has an on-board EQ and all that, but I thought I'd build this simple circuit just to see how it works and it actually made my guitar sound better.

One of the main problems that piezo equipped guitars have is they need to feed a very high impedance input or the sound will suffer badly - not much low end and the mids and highs won't sound that good, either. This is one reason why an acoustic-electric plugged into a regular guitar amp usually doesn't sound very good. With this circuit, it can make it sound much better when your guitar is used with a regular guitar amp. It does so by presenting the piezo pickups with a very input impedance which is presented by the FET. The output impedance is much lower in comparision and is akin to the outout impedance of a stompbox. This is what makes the circuit suitable for using a piezo equipped guitar for use with a regular guitar amp. Below are some details of this project.


Here are some pictures of my project:


My "little black box" is a project enclosure from RadioShack which measures approx. 4"x2"x1" and is made out of some tough plastic. I used a some paper graphics for labeling it, which is glued to the enclosure and protected by some clear tape. It's not the world's greatest quality, but I really only put the label on there to help me remember what does what.

Here is the inside. Everything barely fits in there, but it worked out pretty well. The circuit is built on a piece of perfboard that measures about 1.5"x1", just a scrap actually.

Here's a little closer view of the circuit board. The gain switch can be seen at the upper part of the picture. The inside of the box and the cover are both shielded with aluminum tape.

I used a socket for the FET so I could experiment with different FETs at a later date. Total time spent on the project was about 2.5 hours.

Overall, this is a handy circuit for use with piezo equipped guitars. It's simple, inexpensive and can be built quickly with the most basic of tools. I'd recommend this circuit if you are looking for something simple and effective to use with your piezo equipped guitar. I used it the morning after I built if for about an hour, and I must say that it makes a huge difference with my
Parker Mojo Nitefly's piezo pickups. It actually sounds like an acoustic guitar when plugged into something designed for conventional magnetic pickups. Now I have an idea to combine this buffer circuit with my stereo splitter box for an all in one unit. Could be pretty handy for Parker Fly owners...

Perfboard Layout

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