AM8131 – Audio Mixer (100M)

Roland 131 Module

Overview  The Roland 131 was a four channel audio mixer and output stage, that was launched in 1979 along with the core Roland 100M VCO, VCF and VCA modules. It was not part of the base “D Set” system of 5 modules, but Roland sold around 1000 units over the next 3 years. It was particular useful in large multi-cabinet setups, to enable mixing of many sounds into a final output mixer with headphones and 6.35mm jack sockets.

I built a couple of 100M clones in 2009 using rotary pots in a FracRac format that predates Eurorack. I designed the AM8131 in 2009 but more exciting filter projects took priority. In 2018 I revisited the module using slide potentiometers but it never made it into production, and in 2020 Behringer created their own version. Initially Behringer envisaged a standalone 131 module but they decided to merge it with the 174 Parametric EQ and created the 305 module.

The Behringer 305 is cost effective (if you want both modules), and it works best as “the last” module and not as an interim module to mix audio signals.  The AM8131 is vestaile and can be patched before VCF or VCA modules or used as a final audio output mixer into external recording.

Euro Rack Module:  16HP wide
User Manual:             
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AM8131 Module

The AM8131 Module Each channel has its own input and 30mm slide potentiometer with subtle green LED lighting. The original circuit has been modernised with RC4580 Op Amps and a different approach to panning has been taken, which removes the need for dual antilog/log slider pots.

There are rotary pots for channel panning and master volume, with green LED’s indicating the signal level on each output (Right, Left, Mono). The 16HP panel width enables Roland 100M style control knobs to be used for panning and a larger knob for master volume.

The original Roland design was intended for connecting the output of the mixer to external audio equipment, and the output is set at 775mV RMS (2.2V ptp). The AM8132 has three jumpers (left, right, mono) to set the output level to either 775mV RMS for patching into a mixer or audio interface, or a higher level of 7V ptp for patching back into a Eurorack system.  The jumpers are on the rear of the PCB so that customers can change the settings.

AM8131 PCB

There are seven 3.5 mm jack sockets on the front panel:

  • 4x audio signal inputs for each mixer
  • Stereo Outputs: Left and Right
  • Mono Output

Outcomes & Availability The AM8131 was developed at the end of 2022 and a prototype successfully tested in January. The powder coated panel was manufactured in April and production modules are now available to purchase on our web store.




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