AM8105

Analog Metropolis AM8105 Super JX VCF & VCA Project Notes V1.0 © Analog Metropolis 2014 Rob Keeble Contact: [email protected] Web Site: www.amsynths.co.uk 30 May 2014 AM8105 Module – Super JX VCF & VCA 1 Module Description This module is a clone of the 24dB Low Pass Filter and Voltage Controlled Amplifier in the Roland JX-8P. The circuit is based around the Roland IR3R05 chip which first appeared in the MKS80 REV5 replacing the IR3109 and CEM3360, and then made its way into the JX-8P, MKS70, JX10 and Alpha Junos. The filter and VCA was usually followed by a 1-pole High Pass Filter in these polyphonic analog synthesizers. 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 two 2-pole State Variable Filters configured as a 4-pole Low Pass filter only. The chip has external capacitors with two internal VCA; one for voltage controlled Resonance and one as the final VCA in the signal chain - with both Exponential and Linear voltage control. The IR3R05 is probably based on the IR3109 OTA components but wired on the chip die as 2x SVF. The chip replaced two IR3109 in the MKS80, which were configured as state variable filters, but both running as 2-pole Low Pass filters. The change to the IR3R05 chip was to eliminate the waveform clipping when the IR3109 filters were used in Unison mode. The IR3R05 does not go into self oscillation at high Resonance levels, this is a del...