TS-50 Guitar Preamp

The TS-50 Guitar Preamp is based on the Traynor TS-50 combo amp, originally released in 1979. It didn’t get as much attention as the bass version, the TS-50B, mainly due to the lack of big-name users, but the circuits are very unique and they don’t resemble anything else that came before or after.

The topology is fairly basic at the beginning of the circuit: an op-amp gain stage with a gyrator (simulated inductor) that boosts the midrange frequencies. This active midrange control is the main difference from the bass version other than the component values and the bright switch on the output volume control. This is then followed by a passive Fender-style tone stack for bass and treble.

After the tone stack, 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.