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AM2000 Module - Eµ Systems VCA
Overview This module
is a clone of the single VCA in the Eµ Systems Analog Modular Syntheszier, called the 2000. Whilst the performance of this VCA has been well and truely superceeded by modern designs, its still nice to have an original Rossum designed
VCA. The Eµ Systems VCA has both linear and exponential control modes, and it is very similar in design to the Roland 704 VCA from the System 700 Modular.
Original Circuit The original Revision 1 design dates back to
the Autumn of 1972 when Dave and Scott were setting up their new synthesizer company in Santa Clara. The 2000 VCA module is based around a CA3080 chip with a pair of NPN/PNP transistors for the exponential converter (called the MP-1 by
Eµ - Matched Pair 1). The linear and exponential control voltages and signal paths use 556 Op Amps, which are higher quality than the contemporary LM301 and 741's, but no longer manufactured.
The VCA control has
both linear and exponential control. From October 1974 the front panel toggle switch had a centre position for simultaneous linear and exponential control. The CA3080 based VCA was a bit noisy, so by 1980 it was replaced by a SSM2010
based version, which improved the S/N ratio and reduced the audio distortion. Hacve a look at the AM2005 module if you want one of this.
Cloned Circuit The clone is exactly the same as the original with a CA3080 core
but with NE5532 Op Amps. The exponential converter has been built from a matched pair of 2N3094/2N3906's put on an 8 pin DIL header. I have added a LED driver circuit for monitoring the audio signal output.
Panel The
front panel is a standard AM design, 90mm wide and 4U high, with black lettering. Controls knobs are standard Eµ Modular designs.
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