AM8109 Module - Roland Jupiter 8 Low Pass Filter

Overview This module is a clone of the Roland Jupiter 8 Low Pass  Filter, which is a 2 and 4 pole OTA design. It uses an actual IR3109 chip. I have kept the design to just the LPF rather than replicating the HPF from the Jupiter 8 as well, that's simply because I have designed a descrete version of this filter the AM8090 which has both high and low pass filters. The IR3109 chip has a set of 4x OTA filter stages, and an exponential CV generator to control the frequency cut off.

AM8109 Module The first stage was to buy an IR3109 chip, and review the Jupiter 8 schematics. I then designed the circuit using Eagle CAD and laided out the PCB, managing to fit the design onto a 100x80mm PCB. I have used polystyrene capacitors for the filter stages and  D80017A clone (15/09/07) from Jeroen Allaert at Analogue Renaissance here>>. I then looked through the Juno 106 schematics and designed both the low and high pass filters. I have added a 2-pole LPF mode by hacking into the D80017A PCB. A PIC micro-cobtroller is used to read both a slider pot for the HPF settings and a switch for 2/4-pole LPF selection, it then controls analog switches in the filter to select the correct filter modes.

The module has the following front panel controls:

• Signal Input Level (x3)
• Frequency, coarse and fine
• Resonance
• CV Level (x2)
• HP filter setting
• Push Button - 2 or 4 pole LPF
• LED for HPF mode
• LED for LPF mode

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, a slider with Juno 106 style knob, a Jupiter 8 style push button and push fit mixer style knobs.

Roland Jupiter 8

PCB