L5 Preamp

From the vendor

A pedal adaptation of the two-channel preamp of the Lab Series L5 amplifier from the late 1970s, often considered to be the best solid-state amp ever designed.

Lab Series is a registered trademark of Gibson Brands. Use of the Lab Series name is not endorsed by Gibson and is used for comparative purposes only.

Project overview

The L5 Preamp is a pedal conversion of the preamp of the Lab Series L5 guitar amplifier, a Moog-designed solid-state amplifier from the late 1970s that is widely considered the best and most tube-like solid-state amplifier ever made. It has two channels which are both merged into a shared distortion/master volume circuit as well as a compressor/limiter.

The original amps had the preamp integrated with the power amp. By splitting out the preamp, we can use this either as a normal pedal in a chain (e.g. tuner → overdrive → L5 Preamp → modulation / delay → amp input) or as a true preamp by plugging its output straight into a power amp (either a dedicated power amp or just the “return” jack of an amp with an effects loop). The main difference will be the volume setting. It’s capable of enormous signal levels, far more than any stompbox—so if you’re using it like a pedal, it’s normal to keep the master volume down really low.

The updated L5 Preamp is a full redesign of our original project from 2016. The biggest difference is that this one is much easier to build, with greatly simplified wiring and a cleaner layout. It also now runs on standard 9V DC power instead of AC like our earlier one.

There are also a few circuit tweaks. The first is a new feature: making the Multifilter section switchable so that it can be applied to either channel. There’s still only one of them, but now people who prefer channel 1 can also experience the unique sounds of the multifilter.

The second tweak was to reconfigure the input op-amp stages as non-inverting, which cuts down on noise and is typically viewed as better design practice. We’ve done simulations and A/B tests to ensure the tone is unchanged.

The third change is to remove the hi/lo switches for each channel, which corresponded to the hi/lo inputs in the original amp, and hardwired it to “Lo” mode (i.e. the one intended for low-level signals, providing more gain boost at the input). The only function of the “Hi” input was to attenuate the input, but the attenuated input sounds dull and lifeless in nearly any normal use case. You’ll generally get better results just turning down the channel volume if the “Lo” input is too hot with your instrument.

We have also created an Interactive BOM tool for this project to help with the build process. Components are grouped by value, and you can click any component to see which other parts have the same value and where they’re located. (Chrome-based browsers only)

Note: This project uses a type of capacitor that has been temporarily discontinued by WIMA. Please see our news article about the issue and the substitution spreadsheet for project-specific recommendations. We are stocking a limited supply in the mean time. The build document has not yet been updated to reflect this.