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AM8105 Module - Roland Super Jupiter VCF/VCA
Overview This
module is a clone of the 24dB Low Pass Filter and Voltage Controlled Amplifier in the Roland JX8P. The circuit is based around the IR3R05 chip which first appeared in the MKS80 REV5 replacing the IR3109 and CEM3360 , and then made its
way into the JX8P, MKS70, JX10 and Alpha Junos. The filter and VCA was usually proceeded by a High Pass Filter.
The IR3R05 was the final analog filter chip designed by Roland, prior to the arrival of digital filter technology in
1985 and the D50. The 14-pin DIL chip contains a 4-pole OTA LPF with external capacitors with VCA's for Resonance control and the final Audio Level with exponential and linear modes. The IR3R05 replaced the IR3109 and CEM3360 in
the MKS80 The Roland description is that this is a State Variable Filter with BP and LP modes internally.
AM8105 Module The first stage was to buy an IR3R05 chip, and review the JX8P and MKS80 schematics. There is is
just a single input for audio signals, which must be reduced down by an Op Amp buffer to +/- 10 mV maximum. The control voltages are as follow:
Frequency -200 mV to +10 mV Resonance 0 to +60 mV VCA Linear 0 to +900 mV (for the ADSR)v VCA Exponential +110 mV to +10 mV
and signal input has to be dropped down to just +/- 10mV. , and t I designed
The module has the following front panel controls:
Signal Input Level (x2) VCF Frequency VCF Resonance VCF LFO/Modulation VCF Envelope VCF Keyboard VCF Mode (4 way) VCA Level VCA Mode (2 way)
There are six 3.5 mm 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, and push fit mixer style knobs.
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