RS-80

Voltage Controlled LFO, forerunner to the RS-85

INTRODUCTION
Not all periodic oscillations occur within the range of audible frequencies, but this does not mean that you can not hear them. For example, a violinist’s vibrato may take the form of an oscillation at, say, 5Hz, while the growl produced by over-blowing a brass instrument may occur at 18Hz. Even in isolation, you may hear a periodic waveform at subsonic frequencies - for example, a clock oscillator with an output of 1Hz will sound like a series of repeating clicks. (Strictly speaking, these have a high bandwidth due to the transient nature of the waveform, and you would not hear a sine wave at the same frequency, but that is not the point.)

Synthesisers have a class of oscillators - Low Frequency Oscillators (LFOs) - that create these, and many other, effects. They can add vibrato to a sound, produce growl, act as low frequency clocks and, on some synthesisers, double as audio frequency oscillators.

IN USE
The RS80 is a flexible LFO with an extremely low minimum frequency (one cycle every 50 seconds) that allows you to create a variety of slowly varying modulations and effects. Its maximum frequency lies in the middle of the audio range. The RS80 can, therefore, be used in three ways: as a low frequency modulator; as an audio frequency modulator; and as a secondary sound source. It is therefore vital that, just like a primary audio oscillator, the RS80 exhibits pitch stability, waveform accuracy, and a lack of unwanted noise and/or distortion.

The operation of an LFO may be divided into three major categories: its frequency, its waveform, and its level.

FREQUENCY
The FREQUENCY knob has two ranges:

 HIGH
Turning the FREQUENCY control from its minimum to its maximum will cause the RS80 to produce its upper range of frequencies from 3Hz to 1,400Hz.

 LOW
Turning the FREQUENCY control from its minimum to its maximum will cause the RS80 to produce its lower range of frequencies from 0.02Hz to 5Hz. #

You may control the LFO rate by applying a suitable CV to the LINEAR CV IN socket. This conforms to the Hz/Volt standard used by Yamaha and most Korg monosynths. If you use it as a conventional oscillator you will find that the it produces a different tone to the RS90, adding flexibility to the synthesiser.

Waveforms
The RS80 generates four waveforms simultaneously. The first two of these are the sine wave and the triangle wave, which are often used for imitating acoustic characteristics such as vibrato and tremolo. The square wave is suitable for acoustic effects such as trills, as well as for controlling many other aspects of the synthesiser. Finally, there is the sawtooth wave, which can assume both rising- and falling- shapes.

 SINE
This has no associated level control and, in normal use (i.e. with no oscillator sync applied), it outputs a ±5V sine wave at the current LFO frequency.

 TRIANGLE
The level of the triangle wave is controlled using the associated LEVEL control, and has a maximum output of ±5V.

 SQUARE WAVE
The level of the square wave is controlled using the associated LEVEL control, and has a maximum output of ±5V.

 SAWTOOTH
The level of the sawtooth wave is controlled using the associated LEVEL control, and has a maximum output of ±5V. The sawtooth waveform can be inverted from a rising sawtooth to a falling sawtooth waveform by turning the LEVEL control from its fully anticlockwise position through to its most clockwise position. No output will be obtained when the knob is at its "12 o'clock" position.

Reset In
The RS80 offers a reset input ('sync') that allows you to re-initialise the LFO waveform by applying a second waveform at the RESET input. This re-initialises the LFO waveform every time a positive-going voltage is detected. If the reset signal is a low-frequency periodic waveform, it will retrigger the RS80. If the reset signal is a mid- or high-frequency period waveform, it will act as a 'sync' input, increasing the harmonic complexity of the waveform generated by the RS80. If the reset signal is aperiodic, more complex effects will occur.

Status LED
The status LED gives you a direct visual indication of the LFO frequency.

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