The Delta-Trem is a sophisticated pedal with many possibilities for tweaking the L.F.O. to generate different tremolo characteristic throbs. With this pedal design, I was aiming to get as much flexibility in a compact unit whilst keeping the look of the pedal conservative/traditional.
The way “Setup Mode” operates is as follows. When the “Speed” knob is rotated fully anticlockwise the L.F.O. will modulate at a predefined rate and the “Shape” knob functions as mode selector allowing one of 4 modes to be selected:
- Shape knob controls amp waveforms – ping-pong mode
- Shape knob controls Leslie waveforms – ping-pong mode
- Shape knob controls Amp waveforms – independent L.F.O. mode where the Depth knob acts as a control for the second L.F.O.
- Shape knob controls Leslie waveforms – independent L.F.O. mode where the Depth knob acts as a control for the second L.F.O.
Imagine the Shape knob is like a clock face where mode one is roughly 6 to 9 o’clock, mode two is 9 to 12 o’clock, mode three is 12 to 3 o’clock and mode four is 3 to 6 o’clock. Once the mode has been selected with the shape knob, rotate the speed knob out of the fully anticlockwise position, say 12 o’clock and you’ll be back into normal mode.
There are a lot of functions in the Delta-Trem pedal to allow for a great deal of flexibility and options, however this comes at the price of some extra complexity in operation.
The Delta-Trem is a photo-optical tremolo, not bias modulation tremolo. Signal modulation tremolo based on photo-cell circuitry is more costly to implement than bias modulation designs because it requires extra tubes and photo-cells, however is preferred for the following reasons. Bias Modulation tremolos work by altering the cathode bias to the power tubes in the output section and forcing the tube into “cut-off”. This introduces “crossover distortion”, which is a nasty, odd-harmonic distortion caused by the fact that the signal is not being accurately reproduced. This inherently less costly, less complex circuitry is usually reserved for lower-power, inexpensive amps, such as the ’64 Fender ‘Princeton’.
The Delta-Trem emulate a bias tremolo. One of my customers has spent some time on this and provided some settings: Mode: Leslie Shape: 11 o’clock Depth: Full Speed: 3 o’clockish The key to the bias trem effect is the asymmetrical wave coupled with smoothed peaks. Obviously speed and depth are to taste but this is a good demonstration of the full on effect.