AM8106 Module - Roland Juno 106 Filter

Overview This module is a clone of the Roland Juno 106 Low Pass  Filter, which is based upon the Roland D80017A chip and a seperate 2-pole High Pass Filter circuit. My design uses a D80017A chip clone, but I have also designed a descrete version of the Roland 4-pole OTA based low pass filter - AM8090.

The original circuit is a classic 4-pole OTA based low pass which can be traced back to the mid 1970's, but all the IC's, capacitors and resistors are surface mounted devices, mounted on a 46x17mm black encapsulated PCB. The Juno-106 filter contributes a lot to the warm analog sound of the synthesizer and makes it a very popular analog polysynth on the secondhand market. Owners say the filter is softer, and not so aggressive as earlier Roland filters and possibly more plastic or sandy. This could be due to the use of SMD ceramic capacitors rather than high quality polystyrene "Through Hole" capacitors from earlier designs.

The Juno 106 also has a 2-pole High Pass filter which does not have a traditional variable Frequency control, but instead has 4 fixed filter responses controlled by the on board micro-controller:

• High Pass Filter setting 1
• High Pass Filter setting 2
• No filtering
• Low frequency boost

Quite an interesting set of filters, so I have cloned them both.

AM8106 The first stage was to buy a 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 Juno 106

PCB