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.

Picture 9 - Finished box

Picture 10 - Finished box, battery fits inside very well

Picture 11 - Finished box

Danelectro piezo pickup

Hi,

in this post, I will talk about installing a piezo pickup on my Danelectro DC59. I always kind of wanted a piezo pickup on any of my electric guitars. I noticed that there are bridges with piezo saddles on the market, for Les Pauls and probably for other guitars. But those are not cheap, they're not incredibly expensive, but at the time, I did not want to invest in it.

But now that I got into DIY, things have changed. I came across a video on Youtube (here is a LINK), it explains what a piezo is and how to use it as a contact microphone. It also comes with a schematic for a preamplifier, which I'll show you in another post.

So I decided to build myself a piezo contact microphone and use it on my electric guitars. I bought a medium-sized piezo disc, which I wired as shown in the video above. I placed it on the body of my Danelectro, near the bridge. The sound was garbage and it amplified a lot of unwanted things like me touching the guitar (which was obvious). I tried the same thing with my Les Paul with similar results. Then I tried to place the disc on the headstock, just like you would do with some tuners. Results with the Danelectro were again garbage, but with Les Paul, the sound was actually awesome. But having a piezo disc on your headstock with cables going from it is not exactly pretty. And it still picked up a lot of unwanted sounds.

Then it was obvious that it would have to be placed directly on the bridge. I decided to try it with Danelectro first, because its bridge is a Badass wraparound, with very nice place on the bottom for something like a piezo membrane. Unfortunately, I didn't take a photo of the bridge before placing the piezos inside, but you can google it with ease.

I bought a few piezo discs. It's a thin metal disc, 31mm in diameter, with 18mm of the actual crystal in the center of it. When buying these, watch for these diameters, vendors in my country only show the metal disc diameter, which is kind of useless if you want to cut these metal discs away, like me. For example these 31mm discs have the same sized crystals like the 27mm ones, but those 31s were cheaper for some reason, so I didn't really care.

Then I proceeded to cut these discs to shape, I used three, one was cut on four sides into a rectangle and the other two were cut on three sides, so that there would be that metal overhang on both sides, for soldering a ground wire (which is not really necessary on both sides, but it looks better when it is symmetric, and since the bridge itself is grounded, there is really no need for an extra ground wire coming from the discs). Again, I don't have a photo of the whole pickup before it was put on the bridge, so at least I made this picture:

Picture 1 - Red lines are cuts to make the outer pieces, with the green one to make the center piece, blue and black dots are solder joints.

Be careful when cutting the disc, the ceramic middle is very fragile. I used regular tin snips without trouble. Also soldering the middle is kind of tricky as it can easily melt away if you heat it too much, the soldering iron must be in contact with it for only one or two seconds. There are many posts or videos on the internet about soldering piezo disc so look those up.

When the threes discs were shaped and wires soldered to them, I used epoxy to glue it to the bridge.

Picture 2 - Whole pickup is being held in place while the epoxy hardens.

Picture 3 - Pickup is finished.

In the third picture, there is a finished pickup, but it wouldn't work like this, because as I found out, the strings are touching the pickup (cutting through epoxy) and therefore shorting it out. So I covered it with a tape (picture 4). It worked for a few hours, then the strings cut through the tape. As you can see in picture 5, I put a piece of metal beneath the strings in place where they shorted the discs, so the pressure from the strings is more divided on much bigger area.

Picture 4 - Pickup covered with tape.

Picture 5 - Thin piece of metal to prevent shorting.

Picture 6 - Tiny hole drilled for the piezo pickup wires.

The piezo hot wire is wired to a stereo output jack (the middle part of the jack, tip is still the hot output from magnetic pickups, sleeve is a common ground for both pickups) which replaced the original mono jack on the guitar. When a mono instrument cable is connected, the piezo pickup is shorted out. More on that in the post about the preamplifier used with this.

Also while the guitar was dismantled, I thought it would be a good idea to shield it better (it was not shielded at all - loud hum). It's usually done with copper tape, but I didn't have it and it's very expensive. Tin foil is a good replacement, secured in place with double-sided tape. In the pictures, it looks very crappy, because it was not easy to place it inside the guitar, but it works like a charm anyway, so that is good enough for me. I also replaced the pickup wires with shielded microphone cables (they are not the same because of the way the Danelectro is wired, the thicker one is stereo, thinner one mono - it looks little bit silly, but I had those cables lying around so why not use them).

Picture 7

Picture 8 - Pickguard shielded

Picture 9 - Insides of the guitar shielded - not pretty, but works flawlessly. The pickup hole and that bridge recess kind of looks like a face doesn't it? :/

Picture 10 - Pickup wires replaced by shielded microphone cables, solder joints near the pickups covered with tin foil and tape for maximum shielding.

So that's it, I hope someone will find this helpful :)

Oh and it wouldn't be complete without a sound sample, so here it is, just a quick recording to give you an idea on how the sound changes from regular magnetic pickups, as you can hear, it's not exactly an acoustic guitar sound, so I'm thinking of building one of those acoustic simulators for it. Recorded using a Fender Mustang.

LINK to Youtube