AM8060 Module - Roland Jupiter 6 Multi-Mode VCF

  Play the Demo Sample

Overview This module is a clone of the Roland Jupiter 6 voltage controlled filter which comprises two 2-pole OTA filters in series, and was launched in 1983. Each 2-pole filter can be switched into either Low Pass or High Pass modes providing three VCF modes all with variable resonance:

• 24dB Low Pass Filter
• 24dB High Pass Filter
• 12dB Band Pass Filter

The AM8060 module uses the original Roland IR3109 OTA chip as the core of the filter. I have salvaged two of these chips from an old Boss PH-2 Super Phaser pedal. This Phaser is really quite useless and the PH-2 can be bought for 30 to 40 UK pounds. It provides not only 2x IR3109 but a M5218 low noise Dual Op Amp, 5x IR9022 Dual low power Op Amps, a 4053 analog switch and NE570. The original filter in the Jupiter 6 (and MKS80 REV04) use two IR3109 chips, one as the filter cores and the other to control RESONANCE level as a dual VCA.

AM8060 Module The circuit is based directly on the Roland Jupiter 6 filter even though the original schematics do not show the resistor array values. Fortunately the MKS80 schematic does show the values (The MKS80 REV04 version is implemented as just a single 24dB low pass filter). Having already built an IR3109 based Low Pass Filter from the Jupiter 8 it was easy to replicate the frequency circuit I had designed for this earlier module. The audio signal level is buffered and reduced down before going to the filter core, and then boosted back up after the core.

The filter response of both 2-pole filters can be manually switched between low and high pass 24dB modes, and when the filters are set to Low and High you get the 12dB Band Pass. I could have added 12dB outputs, but that would have meant more PCB space and its packed already to fit into my standard 80 x 100mm.

The module has the following front panel controls:

• Signal Input Level (x3)
• Frequency
• Resonance
• CV Level (x2)
• Push Button (x2) - filter modes

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

Outcome The CAD files were designed in March 2010 and a PCB ordered from Olimex. The PCB arrived in April and went together easily, however there are a large number of parts and the signal tracks are narrow at 10 mil, so care is needed. The frequency response trimmed up nicely to give a good range and cutoff at low frequencies in LP mode, and the converse in high pass mode. It uses the same design I successfully proved in my Jupiter 8 filter clone, complete with Tempco resistor (AM8109). All 3 filter modes work properly, the type of Band Pass response varies between the 2 options of (LP+HP) or (HP+LP), one version has a narrower band than the other.

The Resonance voltage control I designed for the prototype was not suitable, as I had aimed for 0 to +60mV on Pin 9 of the second IR3109 but it turns out the voltage range is more like -120mV to +120mV, so this needed a little Op Amp circuit adding via Veroboard on the prototype PCB. Production PCB's have the revised Q control on the main PCB, it shares the CV Op Amp which is now a Dual version at the bottom of the PCB - pictured on the right.

The OTA capacitors are 330pF Polypropylene versions (the red boxes in the picture), which I matched to within 1%. The M5218 low noise Op Amp in the original pedal and Jupiter 6 was replaced with a TL072 which sounded a lot better. I tried a few Op Amps in this position, ranging from bipolar NE5532 to the high grade OPA2134, but the trusty TL072 sounded the best. There are some abnormalities in terms of frequency response at higher cutoff which are minimized by the TL072.

Overall the filter sounds very smooth with a nice wide range of resonance up to and including full oscillation (60 Hz to over 14 kHz), the high pass and band pass modes provide very useful additional sonic possibilities. Sounds just like my old Jupiter 6, but a lot cheaper than the second hand price. The total cost for this module is less than 100 UK pounds.

Front Panel The front panel is a 3" wide FracRac with Alpha rotary potentiometers and push fit 15mm mixer style knobs.
 

AM8060 Eagle CAD Files REV04