The SEM allows the tone of a single-ended amp to be produced by any push-pull fixed-bias or cathode-biased amp. It also allows for any blend of those sounds with a continuously variable control. The SEM also is often described as "poor man's Power Scaling", as it offers a significant power reduction and early overdrive of the amp. This has been a feature of London Power's own amps for many years, and players call it "the tone control I've been looking for on every amp I ever owned".

For players considering "black-facing" their Fender amp, the SEM offers dialable black-face sound without sacrificing silver-face stability.

The installer of this mod should be able to recognize the relevant circuit points without a layout or schematic for the subject amp.

The SEM comes with notes including installation tips and connection diagrams.