JHS SD-1 Pro Rhythm

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Rare analogue drum synthesizer from the late 70's from John Hornby Skewes (JHS). The SD-1 is a battery powered drum synth with sound shaping controls and a rubber pad which, when hit, triggers the analogue circuitry for an infinite variety of possible sounds from deep bass to high pitches to sweeping disco tones. It can be mounted on its stand to provide a drummer with a pre-determined sound of choice to augment his kit or it can be used as-is in a studio setting for hands-on tweaking. In the latter case this can provide huge amounts of sample material.

The controls are as follows:

- VCO 1 Freq.
- VCO 1 Square/Noise/Ring selection switch

- VCF Freq.
- VCF LP/BP/HP selection switch
- VCF Reso

- VCO 2 Freq.
- VCO 2 LFO/OFF/Squiggle (hf modulation) selection switch
- VCO 2 Modulation Amount to VCO1 or VCF

- Sweep VCO 1/2 Selection Switch
- Sweep VCO Direction/Amount
- Sweep VCF Direction/Amount
- Sweep Decay

- VCA Decay
- VCA Volume"

From JHS:

"The JHS Pro–Rhythm is a self contained drum synthesizer,featuring two V.C.O.s', a ring modulator, resonance control, L.F.O., white noise source, a sweep generator for oscillators, area V.C.A. Section. Thanks to it's advanced features and state-of-the-art circuitry, the JHS Pro Rhythm offers the modern percussionist an expanded form of electronic musical expression previously available only to guitarists and keyboard players. The control panel is rim mounted and designed for easy accessibility and fine adjustment, the control themselves are rationally laid out, and easy to operate. The Instrument is supplied complete with a chrome plated stand which is fully adjustable for height and synth angle. The drum head is a tough rubber pressure pad which gives good response and stick bounce. At certain settings it is touch-sensitive, responding differently to varying degrees of stick pressure. The casing is extremely sturdy pressed steel, finished in matt black. The instrument is powered by two 9 v (PP3) batteries, and is switched on by inserting a jack plug into the output socket. The Controls of the JHS Pro-Rhythm Drum -Synth are split into5 sections , which can be briefly summed up as follows, reading anti-clockwise around the rim of the instrument:

A. VCO1 this is the first oscillator and provides the main sound source.
B. VCF this is the filter which enables the player to add to or subtract from the harmonic content of the sound so as to alter its “colour”
C. VCO2 the second oscillator, which provides a choice between LPO (for modulation effects) and sine wave forms.
D. sweep this section generates and varies the rise and fall in the sound “envelope” as used in a lot of today's popular music.
E. VCA This section controls the overall decay time and overall volume. Only by constant experimentation can the musician build up his own individual repertoire of sounds and effects'"