The P-Retro is a simple but flexible active/passivebass preamp equaliser which offers huge tonal variation to one of the most popular styles of bass of all time, without the need to permanently modify the instrument itself. P-Retro features two stacked knobs each with a pull-switch, class A FET input stage and a high quality relay for pure passive bypass. Power is provided by an internal rechargeable battery. The normal volume control becomes the Volume/Tone Stack and works in exactly the same way as the P style bass original controls, passing the passive signal directly to the jack. When the volume control is pulled up, the active circuit is switched in, post passive tone control, and adds 2.5dB of gain with a flat response. Additionally, the upper knob allows either a mid boost, or a combined bass/treble boost. The lower knob sets the variable frequency points for either mode.