The L4 Bass Preamp is a pedal adaptation of the two-channel preamp of the Lab Series L4 bass amplifier from the late 1970s. It is based on the preamp section of the Lab Series L4 bass amplifier, which was released in 1977. The L4 is a 200-watt head that was originally sold with a matching 2×15 cabinet.

The Lab Series brand was owned by Norlin, who also owned Moog. Moog was responsible for the design of the Lab Series lineup, including the L4. The L4 and its single-channel sibling, the L2, used the circuit of the Lab Series L5 guitar amp as a starting point for the preamp design.

The overall topology of the L4 Bass Preamp is similar to the L5, with tweaks to the frequencies to make it better suited for bass. The tone controls, overdrive, and limiter sections are nearly identical to the L5. The major difference is the addition of a low-noise input section for the second channel, designed specifically for passive bass guitars. The “Bright” switches on each channel have been replaced with “Deep” switches to enhance the bass frequencies. The multifilter feature, which enhanced upper frequencies, was removed since it is less important for bass.

The L4 Bass Preamp project closely replicates the original L4 amp, with the only substantial change being the conversion of the input stage of channel 1 from inverting to non-inverting to reduce noise. The input impedance and frequency response remain the same as the original amp’s “Lo” input.

Channel 2 is unchanged, except for the conversion of the complex switching jacks into an internal slide switch. It is recommended to keep the second channel in the higher-gain mode all the time, even when using an active bass, as it provides more gain and can be turned down as needed. However, the low-gain mode is still available if desired.

An Interactive BOM tool has been created for this project to assist with the build process. It groups components by value and allows users to click on a component to see which other parts have the same value and where they are located. This tool is compatible with Chrome-based browsers only.

Summary created by AI from the original source.