Features a switchable onboard preamp with bass/treble controls. The preamp or gain control works differently on different guitar amp designs. It had a single GZ34 rectifier, two 5881/6L6GC power tubes and four 12AX7 preamp tubes. Electrical Audio produces a two channel microphone preamp (EAPreq) and Mid Side Matrix. Combinations of these types of pickups may be used, with an integral mixer/preamp/graphic equalizer. It is also used by Slate Digital for the VMS1 microphone preamp. The sound was then fed directly into a preamp with no equalization. Some homemade stomp boxes include customized features such as a built-in preamp or equalizer. The line was launched with three products&colon; the Gain Cell DAC/preamp. All wired to the onboard preamp which has 3 knobs for volume, tone, and blend. This eliminates the need for a combo preamp. Tom Walker played a large part in the design of the bass preamp. It houses eight 6550 power valves plus three ECC83 and one ECC82 preamp valves. The Sustainor was essentially a configurable two-channel preamp with compression. The electronics were the Jackson J-50BC pickup with JE-1000 preamp.