AM8120 VCF & VCA (100M)


AM8120 Module

Overview The AM8120 is a replica of the Roland 100M 120 module, a prototype that Roland conceived in 1978. It was a combination of the 24dB OTA filter from the 121 module and the VCA from the 130, which has linear and exponential modes. A marriage of two existing modules was also envisaged in the 111 prototype (VCO + VCF).

A re-imagined 120 module could overcome the limitation of the single 100M filter type, and add an alternative VCF. There are many excellent Roland designs to choose from; Jupiter 8, Jupiter 6, 700 Modular.

EuroRack Module: 16HP wide
User Manual:           AM8120 User Manual

AM8120 Mockup

Module Description  The AM8120 has the same VCA circuit as the original, using half of an AS662 OTA chip. The VCF is based on the AS3109 with 12 and 24dB filter modes. The Q compensation has been implemented with the other half of the AS662. This ensures no signal level drop at higher resonance settings, and enables external CV control of resonance. The filter is trimmed to just touch into self oscillation.

The module is 16HP wide and has two PCB’s. The front PCB holds the jack sockets and potentiometers, with SMD Op Amps providing input signal and CV mixing. The main PCB has the VCF and VCA as well as the LED drivers. The PCB is 80mm wide and contains a lot of circuits, so SMD and 1/8W resistors have been used. The output of the VCF is normalised into the first signal input of the VCA.

The physical design uses tall trimmers for signal and CV adjustment, slide potentiometers with subtle green LED’s and a rotary pot for VCA gain.

Front Panel The AM8120 is the second AMsynths module to use a powder coated front panel with white silk screen printing. The basic panel and holes was drawn with Front Panel Designer and exported as a DXF file. This was then imported into Illustrator and used as a background layer to position and draw the lettering. The finished drawing was exported as a 300 dpi PDF and sent for manufacturing along with the DXF file and the choice of panel colour (Pantone Mid Grey 5U).

Module Outcome & Availability  The AM8120 was developed in late 2022 and production modules with grey powder coated panels will be available in 2023.

 

 

 

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