AM8009 SH-5 LFO’s and S&H

SH-5 Modulators

Overview  This is replica of the two LFO’s, Noise, and Sample & Hold circuits in the Roland SH-5 monophonic synthesizer introduced in 1976. They provide the versatile modulation capabilities that this synthesizer is famous for, and form the left hand section of the main panel. Whilst there are more sophisticated LFO’s in later Roland designs such as the Jupiter 8, it is nice to have transistor based designs with the unique waveforms and frequency ranges they have.

Euro Rack Module:   18HP wide
User Manual:          Download PDF

Detailed Description  The AMSynths circuit is similar to the original and based around the same JFET’s and UJT transistors, with 741 and 1458 IC’s. LFO-1 is a basic affair with just a sawtooth and inverted sawtooth waveform, whilst LFO-2 has a wider range of waveforms; triangle, square and sine (which can be delayed).  There are red LED indicators for LFO-1 and LFO-2 rate.

A transistor in avalanche mode is used to generate white or pink noise, The Sample and Hold circuit is driven by its own internal clock (rate set by sample time) and can sample either LFO1 sawtooth, LFO2 triangle or the Noise output. This approach enables the traditional random step waveforms as well as more predictable patterns. The LFO’s have a frequency range from 0.1Hz to 20Hz.

The panel design uses rotary controls to ensure an accurate value match, with one slide potentiometer for LFO-1 Rate.

There are seven 3.5 mm jack sockets on the base of the front panel:

  • LFO-1 output
  • LFO-2 triangle
  • LFO-2 square
  • LFO-2 inverted square
  • LFO-2 sine with delay up to 4 seconds
  • White or pink Noise
  • Sample and Hold Output
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