Clip-on instrument tuners work by sensing the vibrations of a musical instrument and determine the pitch of the individual strings. They are manufactured in massive quantities and are incredibly inexpensive and readily available. A small inexpensive tuner like this can be useful when playing or calibrating an analog synthesizer. Here’s an easy way to convert a clip-on tuner into a plug-in tuner for use with electronic instruments.
From an electrical standpoint the conversion is very simple. The conversion can be nothing more than removing the piezo disk and adding some wire and a plug. However, It’s a good idea to add some resistance in series with the input if you plan on using the tuner on instruments that operate at greater than line-level voltages like modular synthesizers. This resistance will mimic the output impedance of the piezo disk and limit the current that can flow into the tuner. A series resistor of 200k to 1Meg should work fine, I’m using 649K.
The mechanical part of the conversion is more challenging since we are looking for a connection that is rigid yet adjustable and is light weight so it doesn’t put too much stress on the jack. In the past I have used the metal flex hose from a USB LED lamp and it worked well but it’s not readily available on its own and some parts of the assembly are tricky. For this conversion I’m using 1/4” Loc-Line tubing.
Loc-Line tubing is typically used for delivering coolant to machine tools and for other industrial applications but is also useful for DIY projects. It’s rigid yet adjustable and is easy to assemble and take apart. There are low cost Loc-Line clones but in my experience the genuine Loc-Line brand is worth the extra expense. If you plan on using Loc-Line on more than one or two small projects, I suggest you get the hose assembly tool Mfr #: 78001.
If you are interested in trying this conversion for yourself I have put together a kit with the conversion parts. The kit includes the necessary parts except for the tuner, solder and glue.