Most guitar effects circuits are built into a “stomp box” style metal enclosure such as those available from Hammond, Small Bear Electronics, CE Distribution, and other musical instrument parts suppliers. But smaller circuits can be built right into a guitar within the cavity that holds the volume and tone controls. That lets you quickly switch an effect on and off, without having to find a footswitch to step on. This article shows how to build small circuits into an electric guitar or bass, using a fuzz-tone and wiring for a Fender Telecaster as an example. The fuzz-tone could just as easily be a compressor or other effect small enough to fit inside a guitar. And the guitar could be any model re-wired using the Telecaster examples shown here.
The Wiring
Figure 1 below shows the original wiring for a Fender Telecaster pickup switch at top, with two possible ways to connect a fuzz-tone or other effect below it. The “preferred” wiring method replaces the original volume control with a Bourns 500k potentiometer that has a double pole double throw (DPDT) switch attached. This switch is activated by pulling up on the volume knob.
Two versions of this volume pot are available: the PDB183-GTR01-504A2 has a 3/4” threaded bushing, where the PDB183-GTR31-504A2 shaft is 1.1” long for guitars that require more length. I call this the “preferred” method because the push-pull replacement pot switches the fuzz-tone on and off. Whatever pickup combination is selected goes to the fuzz-tone or not. This also keeps the tone control ahead of the fuzz-tone to allow a “creamy” fuzz sound when desired by fully rolling off the high end. Note that the lower switch half separates the fuzz-tone input from the pickup when the effect is not active, to remove it completely from the signal path.
Note the clever switching arrangement shown in Figure 2, which uses a 1/4” stereo phone jack to enable the battery-powered circuit only when the signal wire is plugged in. Rather than require a separate power switch, this method instead uses the ring contact as a ground return for the battery. A standard 1/4” mono phone plug has a solid metal barrel, so the grounded barrel touches the stereo jack’s ring contact when it’s plugged in.
As far as I know I was the first person to do this back in the 1960s when I designed and built fuzz-tones and other gadgets into electric guitars for myself and other musicians. Today, this is a common feature, not only for electric guitars, but also for tuners and metronomes and other devices that have a 1/4” audio phone jack. Of course, you must remember to unplug the cord when you’re done!
The Fuzz-Tone
There are many ways to design a fuzz-tone effect. You can overdrive a transistor amplifier or add a pair of clipping diodes at the output of an op-amp, or some combination of both or neither. The fuzz-tone design shown in Figure 3 is the original circuit I built back in the 1960s, and I think its sound still holds up well. This circuit is provided as a file in the LTspice format so you can play with it and hear how it works. LTspice is a circuit simulation program that lets you create and test circuits before committing to buying parts and building the device as hardware. I’ve explained LTspice in previous articles, so there’s no need to elaborate here.
Fuzz-tone In.wav is a sample input file available in the Supplementary files on the audioXpress website, though of course you can make your own input files when testing. For Wave files, LTspice considers a full-scale level of 0dBFS to be 2Vpp — 1V in each direction — so the input file was normalized to –10dBFS to approximate the 250mV (RMS) output level typical of passive guitar pickups. The outlined net label Output identifies what’s sent to the output Wave file for you to hear, and Fuzz-tone Out.wav is provided just so you can hear the effect without having to load and run the file.
You can power this circuit from either a standard 9V battery, or 6V from a pair of 3V coin cells wired in series. Either battery type will fit nicely within the Telecaster’s cavity under the tone control. Though when using a 9V battery you should wrap it with electrical tape so its metal case can’t touch the switch or pot terminals. A small wadded up ball of tissue paper will keep the battery from rattling around inside the cavity. The Keystone Electronics 3024 battery holder mounts directly onto a PC board to provide 6V from a pair of 20mm 3V coin cells. Many other dual coin cell holders are available — both PC mount or with connecting wires.
Either way, the average current draw of this circuit is less than 2mA with or without audio. So, it will run for nearly 300 hours on a 9V battery, and about half as long with a pair of 3V 2032 lithium coin cells. For maximum “fuzz” and sustain this circuit requires transistors having very high gain, but the 2N3565 I used years ago is difficult to find today. When using SMD parts on a PC board the BC817-40LT3G is a good substitute and is readily available in small quantities for a very reasonable price. A similar high-gain through-hole NPN transistor is the BC337-40, also commonly available for mere pennies in single quantities.
Avoiding Bad Feedback
Speaking of sustaining notes, electric guitar players often use feedback to make notes continue indefinitely, rather than die out over time as normally occurs. When the amplifier’s volume level is high enough, the acoustic sound in the air reinforces the string’s vibration causing it to keep vibrating in sympathy.
A clever guitar accessory called the EBow can sustain electric guitar notes without requiring feedback or distortion. This device has both a pickup coil and a driver coil—when it’s held above a vibrating string the vibration is picked up, amplified, and fed back to the driver coil. This excites the string at its currently vibrating frequency, sustaining the note until the device is moved away from the string. But when played loudly enough, acoustic feedback can sustain notes as long as desired without requiring such a gadget.
Unfortunately, some guitar pickups feed back by making a nasty high-pitched squealing sound, rather than sustaining notes in a useful fashion. This happens when the pickup coil itself vibrates because its windings are not secure. When I used to modify and repair electric guitars for friends as a hobby, I’d fix this by removing the pickups and soaking them in a tub of hot wax from melted candles. After the wax dried and the pickups were put back into the guitar, they’d no longer squeal when playing loudly, and you could then crank the amplifier level to get the good type of sustaining feedback.
Author’s Note: Portions of this article were excerpted from my upcoming book, The Audio Circuits Cookbook. This book includes more than 80 circuits, with files for every circuit provided in the LTspice format.
Project Files
To download the LTspice file for Ethan Winer’s fuzz-tone, and the sample input and output Wave files, visit the audioXpress Supplementary Material page.
Resources
CE Distribution, LLC, www.cedist.com/products/enclosures
DigiKey, www.digikey.com/en/products/detail/bourns-inc/PDB183-GTR01-504A2/3534261
DikiKey,www.digikey.com/en/products/detail/keystone-electronics/3024/2745771
DigiKey, www.digikey.com/en/products/detail/onsemi/BC817-40LT3G/1475949
Hammond Manufacturing, Ltd., www.hammfg.com/electronics/small-case/diecast/1590-stomp
“LTspice,” Analog Devices, www.analog.com/en/design-center/design-tools-and-calculators/ltspice-simulator.html
Small Bear Electronics, www.smallbear-electronics.mybigcommerce.com/enclosures
E. Winer, “Building a Guitar-Controlled Synthesizer: The Sample & Hold Time Machine,” audioXpress, April 2022.
E. Winer, “Building a Guitar-Controlled Synthesizer: Frequency to Volts and Back,” audioXpress, May 2022.
E. Winer, “Building a Guitar-Controlled Synthesizer: LFO and ADSR,” audioXpress, June 2022.
E. Winer, “Building a Guitar-Controlled Synthesizer: Input Section & Pick Detector,” audioXpress, July 2022.
E. Winer, “Building a Guitar-Controlled Synthesizer:VCA & VCF,” audioXpress, August 2022.
This article was originally published in audioXpress, April 2025
