AM8105 VCF & VCA

AM8105 Roland Super JX Filter and VCA

This module is a clone of the 24dB Low Pass Filter, fixed High Pass Filter and VCA in the Roland Super JX10. 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 fixed High Pass Filter in these polyphonic analog synthesizers. 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 VCF capacitors with two internal VCA’s; one for voltage controlled Resonance and one as the final VCA in the signal chain – with both Exponential and Linear voltage control. The IR3R05 implementation in Roland synths does not go into self oscillation at high Resonance levels, as they wanted to avoid the self oscillation distortion from SVF’s and provide a smoother sound. We have implemented Resonance into self oscillation, so you get the best of both worlds! This module is limited to a production run of 50x.

he AM8105 module uses an original and new Roland IR3R05 chip, which delivers a 4-pole voltage controlled low pass filter, with a smooth and controlled resonance. There is a linear VCA input for connnecting an external ADSR, the VCA exponential input is not used. The VCA is followed by a fixed single pole High Pass Filter which has 2x HP modes and a wicked Bass Boost. These modes are selected by a momentary push button, with LED indicators for all 4 modes (blue, blue, green and red). The front panel has rotary pots for Frequency Cutoff (FREQ) and two frequency modulation pots; CV1 and CV2. The VCA gain is controlled by the GAIN potentiometer, which doubles as ENV level amount when an ADSR with a 0V to +10V signal is connected to the ENV input. A Resonance potentiometer enables increased Q factors into the start of self oscillation and then into full oscillation. The VCF does distort a little at full self oscillation, like most SVF’s, but the journey of resonance provides some really useful and creative sounds. There are 2x signal inputs with level controls (SIGNALA and SIGNALB). This module has a really nice smooth and laid back filter, with the added benefits of an onboard VCA and a fixed filter to cut or boost the output. Just connect one of our dual ADSR’s and a dual VCO and you have a complete synthesizer!

http://www.amsynths.co.uk/products/filters/am8105-super-jx-vcf-vca/