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AM8106 Module - Roland Juno 106 Filter
Overview This module
is a clone of the Roland Juno 106 Low Pass Filter which is based on the Roland 80017A chip and a discrete 2-pole High Pass Filter circuit. The design makes use of the best 80017A clone on the market, which is available from Analogue Renaissance.
The original Roland 80017A circuit is a classic 4-pole OTA based low pass which can be traced back to the late 1970's and the Roland 100M and Jupiter 4. All the IC's, capacitors and resistors are surface mounted devices, contained
in a 46 x 17 mm black encapsulated PCB. In fact some of the resistors are carbon printed, which means they are rather unreliable and the Roland chip is prone to failure - hence the clone being easily available. The 80017A contains an
IR3109 and 2x BA662 OTA chips, the first controls resonance the second is used as the final volume VCA. You can see the insides at Obsolete Technology.
The 80017A filter contributes a lot to the warm analog sound of the
Roland Juno 106 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 sounds 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:
Quite an interesting set of filters, so I have cloned them both, and made use of the VCA circuit in the 80017A.
AM8106 The first stage was to buy a D80017A clone (15/09/07) from Jeroen Allaert at Analogue Renaissance. I
then looked through the Juno 106 schematics and designed both the low and high pass filters. During 2008 I prototyped a micro processor design for switching the high pass filter and using the original Juno 106 sliders. This design
evolved into a complete programmable VCF/VCA/ADSR circuit, which will reappear in 2010 as a separate design. By late 2009 the AM8106 module had been switched back to a more traditional design with a simple miniature 4-way switch to
select HPF settings.
The D80017A is used as a 4-pole LPF with front panels controls for Frequency and Resonance, it is possible to kludge a wire onto the chip to get a 2-pole response but I have left that option out, to keep the
module features within the scope of the original Juno 106. The VCA level is available externally so a control voltage such as an ADSR can be patched in. The VCA level pot defaults to a simple VCA gain when no control voltage is applied.
The circuit has Op Amp buffers before and after the D80017A chip for converting the audio signals to the higher 10V levels used in analog modular systems. The control signals are also designed for the same higher voltages levels and
have appropriate protection so we don't blow up the 80017A chip.
The module has the following front panel controls:
Signal Input Level (x2) Frequency Resonance CV Level (x2) HP filter setting
There are six 3.5 mm jack sockets mounted on the left hand side of the panel, these are:
Signal Inputs (x2) VCF CV Inputs (x2) VCA CV Input Signal Output
Front Panel The front panel is a 3" wide FracRac with Alpha rotary potentiometers, and push fit mixer style knobs.
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