Analogue Systems RS240 FrequencyShifter

Bode type frequency shifter, faithful reproduction of the circuitry of this classic unit.

A frequency shifter is a highly specialised module capable of shifting the spectrum of a signal by a fixed amount. This is very different from a pitch-shifter and other effects such as ring modulation or frequency modulation. The RS240 allows you to shift the frequency linearly within a number of ranges, the widest of which shifts the signal by approximately ±5kHz at its maximum setting. You can use manual and voltage controls (or a combination of the two) to achieve the desired effects. Upwardly shifted and downwardly shifted signals are available simultaneously, both as independent signals, and as a user-defined mix of the two. This module also allows you to shift the frequency exponentially, which will produce a number of conventional - and less conventional - pitch shifting effects.

The RS240 offers two front panel frequency shift controls. These are the large pitch control knob in the centre of the panel, and the scale selector that determines both the maximum amount of shift, and whether this shift is linear (i.e adding an amount to the frequency of the incoming signal) or exponential (multiplying by a factor the frequency of the incoming signal). There are also three CV inputs that allow you to control the amount of pitch shift using external voltage sources. Each of these accepts CVs in the range ±10V. However, the maximum range of the three summed sockets is also ±10V, so you cannot apply +10V to each of the three inputs and expect a frequency shift proportional to +30V.

Pitch Control Knob

You can shift the frequency of the incoming signal between the maximum and minimum ranges shown. The internal CV generated by the knob is equivalent to ±5V (i.e. a 10V range in total) applied to any of the CV1, CV2 or CV3 inputs.

The scale switch has six positions, as follows: Zero, EXP, 5, 50, 500, 5k.

The RS240 offers one signal input and five signal outputs, as follows. The amplitude of the output is approximately equal to that of the input.

Squelch

When the input signal drops below the threshold, a noise gate cuts off the output, thus minimising unwanted noise and artefacts generated from background noise. (The term squelch is an early radio industry term for a noise gate.)

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