Bias tremolo

A tremolo effect produced by varying the bias of the output valves so their gain rises and falls with an oscillator, creating a deep, soft pulse.

Because the oscillation changes how the valves are operating rather than the level of the signal passing through them, bias tremolo has an organic, swelling quality that many players prefer to a hard on-off chop. It also increases distortion slightly as the bias shifts, so the sound thickens as it pulses, and it tends to be more pronounced at moderate volumes. The trade-off is that the effect can be subtle at very low settings and requires careful circuit design to avoid introducing noise.

Example: An amplifier whose tremolo feels like a gentle, breathing sway in the sound rather than a sharp cut is using bias tremolo.

Bias tremolo

See also