|
AM 8121 Module - Roland 100M VCF
Overview This module is a
clone of the VCF from the legendary Roland 100M modular synthesizer. This VCF appeared in two formats:
- a dual LPF in the 110 module
- a LPF and a HPF in the 121 module
It is this later circuit I have cloned, with a simple non-voltage controlled single pole 6dB High Pass Filter in front of a fully voltage controlled
4-pole 24dB Low Pass Filter with resonance into fuill self oscillation.
AM8121 Module The AM circuit is a careful replication of the original
design with the HP and LP filters in series. The LPF is a 4-stage OTA design, which became the basis of the later IR3109 chip in the Jupiter 8. The OTA are BA662's in the original, but I have used the BA6110 which are still available at
a low price. I have modified the CV circuit to make use of easily available 1K tempcos and to use european transistors (2N3904/06), The circuit was designed using Eagle CAD and laided out onto a 80mm x100mm PCB, which is the standard AM
format for FracRacs.
I have used 1% polystyrene capacitors for the filter stages and upgraded the audio path capacitors as well. Basic TL07X Op Amps have also been used along
with 2N5485 FET buffers after each OTA. I have not useitilised the BA6110 buffer, although some other Roland filters used this approach.
The module has the following front panel controls:
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.
|
