Hello

I've started making my own piezo pickups for guitars and ukuleles. I don't want to install them permanently in any instruments and so am experimenting with different means to attach them, scotch tape being my current favorite.

I've built only one so far: a 3/4 inch diameter piezo disc soldered to a short length of guitar cable. I bought the disc from Electronic Goldmine in a three-for-a-dollar package. I bought other discs as well, but these were the only ones with pre-soldered leads. Soldering wires to these discs is incredibly difficult. I pulled off the leads and used the solder already attached to the disc.

After I soldered together the the cable and the disc, I dipped the disc and an inch of the cable into black Plasti-Dip, a weird, and according to the State of California, carcinogenic substance. The idea for dipping the pickup in Plasti-Dip from Nicolas Collins' book Handmade Electronic Music. According to Collins, the Plasti-Dip strengthens the pickup connections, reduces hum, and reduces some of the high frequency resonance of the disc. All these things turned out to be true.
Because piezo pickups have high impedance outputs, they require preamplifiers for better sound. I've used some on hand and built one so far. Here are some sample recordings of the above plasti-dipped pickup and some preamplifiers. The samples are a Mel Bay scale exercise played on a nylon string guitar. I taped the piezo right near the bridge under the high "E."

The first sample was recorded with my recording interface, the Presonus Firebox. It contains its own preamplifiers so I could plug the pickup directly into it. Notably, all of the other samples must go through the Firebox. (Click on the pictures to play the clips.)




The second sample I recorded with the Digitech Genesis 1, an effects unit and amp emulator now discontinued. I bought it new about 6 years ago for $70. All of the settings were set half-way and all of the effects (compressors, noise gates, etc.) turned off. I set the amplifier to "Brit Combo," which supposedly emulates a Vox AC30 -- an odd setting for a nylon string guitar, but it sounded natural.


The third sample I recorded with the "Mint Box Piezo Buffer," a preamplifier I built. I was under the impression when I started building the first pickup that I would need some sort of special preamp, i.e. one that could handle very high impedances. This turned out not to be the case, but building this was lots of fun. The design is by an engineer named Scott Helmke. Scott is a very nice guy and answered many of my dumb questions while I was building this, such as why the tantalum capacitor started smoking the first time I plugged in the battery. The mint box sounds great through an amplifier, much better than a piezo alone. I am disappointed that the recording sounds not so good: too much midrange. But, I believe the Mint Box was designed for live settings.


Finally, I recorded the same exercise using an Audio-Technica Pro 37 microphone as a reference.


I'm happy with the sound of this pickup and think that, for accurate reproduction, the Firebox alone sounds best. I have some more discs and some piezo film I'll write about next time.