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AM8110 Module - Roland 100M VCA
Overview This module is a
clone of the VCA from the legendary Roland 100M modular synthesizer. The VCA appeared in two formats:
- a dual VCA with linear and exponential modes in the 130 module
- a single VCA with linear mode in the 110 module
It is this former circuit I have cloned, with a simple non-voltage controlled High Pass Filter in front of a fully voltage controlled 4-pole 24dB Low
Pass Filter.
AM8120 Module The AM circuit is a careful replication of the original design with both linear and exponential control modes. The
VCA is based on the BA662 OTA chip, which I have replaced with the easier to find BA6110 which has the following specifications:
Whilst this is not a leading edge VCA, these specifications are fine for use within a modular synthesizer and are certainly better than the venerable
CA3080. I have modified the CV circuit to make use of easily available European transistors (2N3904/06), and a TL071 Op Amp in the CV circuit. I have added a simple LED driver to display the post VCA audio level. The circuit was
designed using Eagle CAD and laided out onto a 80mm x100mm PCB, which is the standard AM format for FracRacs.
The module has the following front panel controls:
Initial Gain Signal Input Level (x3) CV Level (x2) LED for post VCA level
There are six 3.5mm jack sockets mounted on the left hand side of the panel, these are:
Signal Inputs (x3) CV Inputs (x2) Signal Output
Front Panel The front panel is a 3" wide FracRac with Alpha rotary potentiometers, with 15mm diameter plastic mixer knobs.
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