The AM8104 replicates the high and low-pass filters from the Roland Jupiter-4 and presents them in a neat and silver Eurorack module.
AMSynths continues its exploration of vintage gear with a modern replica of the two filters found in the 1978 Roland Jupiter-4. It had a 4-pole low pass filter and a single-pole high pass filter based on OTA designs.
To accurately replicate the sound AMSynths is using BA6110 OTA chips in the filter core and polypropylene filter capacitors. Some buffering op-amps are needed to get to appropriate Eurorack levels and the filter uses an OTA in the resonance feedback loop.
The Jupiter-4 was all about the sliders but for the front panel AMSynths has opted to go with knobs for the LPF and a single slider for the HPF. You have CV inputs and attenuators for Envelope and LFO inputs which mimics the modulation options on the synthesizer. There are two audio inputs, both with level controls which can be very useful. There’s also an intriguing KYBD switch that reflects the “KYBD FOLLOW” function on the Jupiter-4. This was used to control the filter with the voltage from the keyboard but you don’t have that information going into the AM8104 so instead AMSynths are tapping into the Doepfer CV Bus system via a 16-pin power connector.
From the manual:
The AM8104 includes a keyboard follow feature which enables the keyboard CV on the Doepfer bus to effect lowpass filter frequency cutoff. Some Eurorack keyboards like the Waldorf KB37 include this signal in the design,alternatively a simple keyboard CVand gate breakout module can be used.
The AM8104 is a tidy looking module, hand-built with decent components and should be available any time now for a reasonable price of £140. No sound demos or videos are available at the time of writing.
More information from AMSynths