The TS-50 Bass Preamp is an adaptation of the Traynor TS-50B, a solid-state bass amplifier that was first released in 1979 and is considered one of the best bass amps ever, with its signature grinding drive tone. It’s far from a clean amplifier, but it imparts its own distinctive character that doesn’t quite sound like anything else. It is notably associated with Bob Weston and Steve Albini (Shellac) and David Wm. Sims (The Jesus Lizard).
The topology is fairly basic at the beginning of the circuit, but after the tone stack it gets interesting. The signal is split into 3 bands (low, medium and high), and each band is run into a pair of PNP transistors that distorts the bands separately before combining them back together. They named this the “Tri-Comp Network”—in this case using the term “compression” to refer to distortion and clipping, as opposed to clean compression as it’s normally thought of today.
Traynor’s lead engineer Eric Von Valtier invented the Tri-Comp Network as a method of rounding out the harsh square waves normally associated with bass distortion (actually more like fuzz). The result was, as they called it, “a round-shouldered, three-tiered pyramid” waveform that resembled a sine wave, but with a jagged sort of clipping that actually occurred within the waveform rather than just cutting off the peak as with most other types of clipping.
The TS-50B was notably adapted by Tronographic for their Rusty Box, first released in 2007 and still in production. The TS-50 Bass Preamp presumably shares a lot in common with the Rusty Box, but we have not seen inside one and our TS-50B is not based directly on that pedal.