The circuitry, utilising a pair of 5670 double triodes, comprises a gain stage directly coupled to a low impedance output buffer. It incorporates 4 inputs and 2 pairs of outputs. Attenuation is via an ALPS motorised potentiometer. The HT power supply is split into two separately filtered rails, one for each channel, while the filament supplies are also smoothed to minimise noise.

The L5 preserves the dynamism & energy inherent in recordings in a way that many passive attenuators do not.