AM8176 Triple Resonator (100M)

Introduction Back in 2009 I replicated many of the Roland 100M modules and built 20 modules into two FracRac cabinets. In 2018 I started recreating my 100M designs into Eurorack but the launch of the Behringer 100M clones in 2020 meant these plans were scrapped.

In 2022 I bought some of the Behringer modules secondhand to use as a new test rig and to check how they are designed. The limitation of only two filter types (24dB LP and EQ) in both the Roland original and the Behringer copy became very apparent. The AMSynths 100M project was restarted as a result but as additional modules, or modules that Behringer have not replicated too well.

The AM8176 Roland never made a resonator circuit but Korg did and put an excellent triple bandpass resonator into the PS3100 synthesizer of 1977. The circuit is quite simple and has three vactrol filters with fixed resonance and variable shared frequency control. A dedicated LFO is used to sweep the resonant peaks.

The AMSynths design uses the same three vactrol based filter circuits but opens up the controls. There are separate inputs and outputs for each filter, along with separate frequency control and resonance. Filter 1 and 2 have a rotary level control, and the third filter has a mix level control for  a summation of all three filter outputs.

over each resonator. The filters are pre-configured to operate in parallel, with signal input 1 normalised to 2 and 3, and the modulation input 1 also normalised to mod 2 and 3. The filters can also be used with 3 separate signal and/or modulation sources or the first two filters can be patched in series. An external LFO (140 or 150) is used to sweep the filter frequency, in fact any CV generating module can be used.

Module Outcomes & Availability The AM8176 module was designed in December 2022 and a second prototype tested in November 2023 (other projects took priority). The design proved sucessful and the module produces some excellent resonant filtering. The module will be available in 2024, please check our webstore for more details.

Copyright AMSynths 2022