DIY electric guitar projects: Piezo pickup preamplifier

Hi,

in this post, I'm going to talk about my piezo preamplifier. As I mentioned in the previous post, the whole idea for a piezo pickup came from a video on Youtube (LINK). In this video, you can find a schematic for this preamplifier circuit, so I won't post it in here (not even sure if I can). Instead of a MPF102 transistor, I used BF245C, simply because I had those at home. No other changes were made to the preamp circuit.

Now lets talk about how I decided to wire the piezo pickup from the guitar. The idea was simple - to not make any, or at least very small, alterations to the actual guitar. So with my Danelectro, I only did two things - drilled a small hole from the bridge recess to the insides for pickup wires, and replaced the original mono jack with a stereo one. Nothing more, except for the actual piezo installation of course.

So the preamplifier, along with other controls, like pickup switch and a volume control, needs to be in some external box or a pedal. I decided to use a box that would hang from the guitar strap, just like for example wireless transmitter boxes.

Picture 1 - Complete circuit. (first version)

Picture 2 - Detail of the preamp board.

In the first picture, you can see the first version of this preamplifier, used in those experiments with just one piezo disc placed on various parts of the guitar body. It still has mono jacks on both ends, no potentiometer for volume control. Revised schematic is in picture 3. As you can see, the switch in one position puts through the magnetic pickup, kills power to the preamp and disconnects its output, the other position does the opposite, obviously.


Picture 3 - Final version of the schematic.

Now for the enclosure. I didn't have any guitar effect enclosure, or any other plastic or metal box ready for this project, but I had a pack of cigarettes and a steel sheet. And as it happens, 9V battery exactly fits in a pack of cigarettes. In the picture 4, there is sort of a steel frame for the box, because obviously just the paper cigarette box wouldn't last very long, so it is "reinforced" like this. The frame is made from two larger sheets forming the top and the bottom and a bent pieces that hold these two sheets together and form the actual space between them. All pieces are glued together using epoxy.


Picture 4 - Steel frame.


Picture 5 - Steel frame, switch yet to be glued to it.

The cigarette box needed to be unwrapped in order to fit the steel frame inside, and while it was like that, I taped a tin foil inside of it, just so it would be shielded a little better, it's probably not necessary because the steel frame should do the shielding quite well.

Picture 6 - Box already with holes for the jacks and control parts


Picture 7 - Top sheet added.

The whole gadget was tested before each important part, because after the addition of the top sheet, it was impossible to do any modifications or repairs. I also made a short stereo cable, simply because this is a DIY blog and also because my local audio stores didn't have any short stereo cables that look any good.

Picture 8 - Home-made stereo cable

After all that, there was just one thing to do - put it all together. So that's it :) It was a nice little project, not very hard. I still need to make something to hold it on the guitar strap, so far I used plastic cable ties as a temporary solution, but will probably use some velcro straps.