The Star Synare is a cool looking synth, like a rubber UFO! It can be triggered by hitting the top pad with a drum stick , the sound is modified by the knobs around the edge. The synthesier consists of 2 oscillators, a noise generator, simple decay envelopes, VCF and VCA. Its pretty cheesy but put to the right settings you can get quite odd sounds. The bassy sounds are the most interesting.

Schematic of original

Clacktronics Star synare copy

A4 PDF Version 

Circuit Description

I copied this schematic from the original Star Synare 3 service manual. It splits the circuit up into its different sections in order to analyze them, I have redrawn it as a complete schematic so you can get an overall image of the design. Its basically a synthesizer minus Voltage controlled oscillators instead it uses manually controlled CMOS inverter oscillators.

A really good feature of the design is the power supply, the circuit that conditions the pulse from the transducer also switches the whole sound circuit off when the drum is not being struck. It does this by feeding the trigger into a darlington pair that is connected between the positive power supply. As it is battery powered this means it prolongs the batteries life, and I am interested to see if this changes the sound? Strangely the manual draws a PNP Darlington pair but lists an NPN type , so in the schematic I have drawn the NPN which seems to make more sense.

The sound generation starts at 2 simple CMOS AND gate oscillators (joined to be inverters) and a noise source based on the standard reverse NPN BE junction. The switches let you toggle noise and oscillators. The mix is then fed into a VCF which the most sophisticated part. It is a full 24dB/Oct filter with resonance then a into the VCA and out.

It is peculiar that Osc2 ( when divided by 20 ) is off at centre position , I wonder whether this is true.

That classic Disco Boooooooowwww comes from the control circuitry that creates envelopes out of the trigger, to get the pitch you actually have to make the filter oscillate.

The most peculiar thing about the circuit is the last OTA (the VCA’s) apparently directly drives the output jack which could cause issues with amp inputs, especially ones with variable loads, this may just be in the service manual!

DIY Schematic

  • Replaced the 3080s with Lm13700s as the 3080 is out of production and because the LM13700s are dual and have integrated buffers.

  • Seperated the OSC2 divider switch

  • single supply or eurorack option

Mods for Original

Probably not the best idea if you have a perfect one (sell it and go on holiday!!) Schematic soon, but Mod ideas are.

  • inter oscillator modulation or sync?

  • OSC2 is sub oscillator

  • 12 dB/Oct switch

  • external in (a bit silly)

Contributed work

Davide Gatti beat me to it! he corrected a few errors in my schematic and created this excellent clone on stripboard. He used the original CA3080’s.