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AM3030 Module - SCI Prophet 5 Revision 1 VCO
Overview This
Voltage Controlled Oscillator (VCO) is based around the classic SSM2030 chip that was used in the original Prophet 5 (Rev 1 and 2). The SSM2030 was the first non-proprietary VCO chip ever produced, Dave Rossum created it in 1977. The
chip was the basis for a number of custom
E-mu Systems synthesizers, as well as the original Prophet 5 and 10. This is a good VCO design which has HF trimming, and the relatively similar performance of each chip within a batch
enabled polyphonic designs. However its performance has been exceeded by more recent discrete designs, although an ultra stable power supply helps alot.
Original Circuit
The original design in the Prophet 5 is very simple, with basic pulse, triangle and sawtooth waveforms being created from the VCO core. This is exactly out of the datasheet with an external tempco resistor (1K 3600ppm) and some simple CV and modulation summing Op Amps.
AM Circuit The Analog Metropolis circuit is based on the original but with soft and hard sync options. The VCO can be switched into LFO mode with a large capacitor, but the cross talk in the wiring makes this an
unstable feature and is therefore not included in the AM design.
The base PCB produces Triangle, Pulse and Sawtooth waveforms. I have added push button control to select the waveforms and sync on/off, using the same momentary
buttons as on the Prophet 5. This makes for a more interesting control surface, complete with red LED indication of the selected waveforms. A high quality audio Op Amp on the back of the switch assembly mixes the selected waveforms into
both a normal and inverted audio output. The switch PCB's are generic and can be used to control any analog synth module. More details on Push Button Sub Module (PBSM) are here. more »
Panel The front panel is a standard AM design, 90mm wide and 4U high, with black lettering. Controls knobs are standard ARP2500-like designs.
Build History
The schematic was transferred into Eagle CAD in July 2005, and prototype boards were sucessfully tested in November 2005. Production boards have been available since January 2006.
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