Guitar Electronics • Custom Circuit

1992 Jackson.
JFET Preamp + Kill Switch.

A custom onboard preamp developed around the guitar’s existing pickups, with adjustable output from a slight cut through clean boost and into light overdrive — plus a momentary kill switch for rapid stutter effects.

1992 JacksonJFET PreampMomentary Kill SwitchCustom Guitar Electronics

Finished 1992 Jackson with added JFET preamp switch, indicator LED and momentary kill switch

01 • The Project

Keep the pickups. Change what they can do.

The customer came in wanting a momentary kill switch for Tom Morello and John 5-style stutter effects. They also weren’t happy with the guitar’s pickups and were considering replacing them with an active set.

Instead of immediately changing the pickups, I showed them a few small onboard preamp ideas that could add output and change the response while keeping the pickups already in the guitar. They chose the preamp route, so the goal became building something specifically around this instrument.

02 • Circuit Development

Developed with the guitar plugged in.

The preamp wasn’t treated as a generic module. The circuit was breadboarded and adjusted while listening to this guitar and these pickups, then transferred to a compact board for installation.

JFET boost circuit being developed on a breadboard beside a hand-drawn schematic — Breadboard development and working circuit notes.

Compact JFET preamp circuit built for installation in the Jackson guitar — The compact circuit after moving off the breadboard.

03 • One Circuit, Several Jobs

From a slight cut to light overdrive.

Trim Down≈ −2 dB

With the internal trim pot all the way down, engaging the circuit gives a small preset level cut.

Trim Up SlightlySubtle Boost

A modest increase in output and response for some of the feel the customer was looking for from an active setup.

Trim Up MoreClean Boost

More level on tap, functioning much like having a clean boost pedal built directly into the guitar.

Trim FullLight Overdrive

At the top of the range the circuit begins pushing beyond a clean level increase into light overdrive.

Rear cavity cover labeled JFET PRE AMP LEVEL MORE LESS — The internal level adjustment is accessible through the rear cover — labeled the same way it works: more or less.

04 • Installation

Fitting the new circuit into the existing guitar.

The finished circuit, battery, switching and wiring all had to live alongside the guitar’s existing electronics. The preamp level is set internally, while the front-mounted switch lets the player bring that preset sound in and out instantly.

A separate momentary switch kills the signal only while it is held, making fast rhythmic cuts and stutter effects possible without changing the player’s normal switching setup.

Jackson guitar electronics cavity during preamp installation

Compact preamp and wiring being installed inside the Jackson control cavity

Completed compact JFET preamp board inside the guitar

05 • The Result

More range without replacing the pickups.

The finished modification kept the existing pickup set while adding an adjustable second level/drive character and the momentary performance effect the customer originally wanted.

Full view of the modified red 1992 Jackson guitar — The finished 1992 Jackson.

Close view of the finished Jackson controls — Front-mounted switching and indicator LED integrated into the existing control layout.

Bench Video

Have an Idea?

Not every modification comes out of a catalog.

If you’ve got an idea for a guitar or electronics project, get in touch and we’ll talk through what’s possible.

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