Unique 1970’s Analogue Synthesizer

via this auction
"It consists of two (19” rack mounting) units (each 3u). I’ll call one the ‘Amp/PSU’ and the other the ‘Synth’

The ‘Amp/PSU’…
Is constructed from tinned steel and aluminium and contains (enclosed) two power transformers (manufactured by GARDNERS – type GR26723 quite large and heavy) and two 20W power amps (Toshiba Power Pack TH9013P - The manufacture dates and availability of the power amps suggest the whole synth was constructed in the mid seventies). There is a mixer/patchbay, a signal preamp (with gain and volume – cw rotation of gain REDUCES the signal), a divide down circuit (?) and a Power (on/off) section which also supplies the power (via a lead) to…

The ‘Synth’…
Two Voltage Controlled Oscillators (VCO) with Low/High switch (can be used as LFO). Square and Triangle outputs.

Ring Mod.

Noise.

Two Voltage Controlled Filters (VCF), one Low Pass and one High Pass.

A ¼” ‘Patchbay’ with ins and outs for the above sections.

An Envelope Generator (EG). The audio signal is fed through it, so I’m assuming there is some form of VCA within the EG. There is also a TRAP out with a level control (I’m assuming TRAP is short for ‘Trapezium’) which can be used as a control voltage.

All of the circuit boards and wiring of the ‘Synth’ are exposed on the back of the 3u panel (not in an enclosure).

*It Works..!
This is a very old (early?) synthesizer, hand built back in the 70’s, so although it 'works', it will need care and attention from its new owner to get the best from it. Some of the pots are ‘crackly’ as well as some of the jack sockets. Eleven of the eighteen (silver) knob caps are missing. There are signals ('square' & 'triangle') from both oscillators and they both switch between high and low. The noise output also works. The Ring Mod appears to work. The filters appear to work (both LP and HP). The output and input jacks (in the colour coded panels on the ‘Synth’) work (some ‘crackling’). The Envelope section works, both in ‘Cycle’ mode (which appears to be a repeating trigger whose time is set by the ‘Rate’ pot) and in ‘Man’ (Manual, triggered by the red push button which is intermittent – needs cleaning?) The inputs and outputs from the Mixer appear to work (some ‘crackling’) and the pre-amp appears to work (with the rather ‘odd’ gain control that reduces the signal when turned clockwise). There’s an amplified signal from both of the power amp outputs. I’m not sure what the ‘panel’ to the left of the ‘Mixers’ does. I assumed that a signal fed to the in socket would appear divided at the (divide by 2, 4 and 8) jacks, but I couldn’t hear anything, so perhaps this part is faulty? Power is via a standard ‘mains’ plug. The ‘Power’ switch works and the neon power light works. I’m assuming the two ‘din’ power (D.C.?) sockets work as the ‘Synth’ plugs into one of them and seems to power-up ok. When powered up there is a ‘hum’ which seems to be ‘mechanical’ and probably from the two Gardner power transformers (could be as simple as loose mounting). It needs a good clean."