AMSynths AM8104, the Roland Jupiter-4 filter as a Eurorack module

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Rob Keeble of AMSynths has pulled the iconic analog lowpass and highpass filter of the Roland Jupiter-4 in a solid silver Eurorack module. 

There are very few novel filter design types. Most of the time, developers use existing designs and implement them in their developments. Either as a complete clone/ replica or in a modified form.

If you want high-quality replica filters of well-known vintage synthesizers as Eurorack modules, you should take a look at the handcrafted modules from Rob Keeble (AMSynths). Recently, he also partnered up with Behringer for the ARP clones (2600, 2500 modules…) or the upcoming MS-5 (Roland SH-5). Today he has added another vintage filter to his portfolio.

AMSynths AM8104

AMSynths AM8104

The AM8104 is a modern replica/clone of the two-filter section found in the Roland Jupiter-4 analog Synthesizer from 1978. It features a 4-pole lowpass filter and a 1-pole highpass filter based on OTA designs. AMSynths uses

Rob Keeble of AMSynths is using the BA6110 OTA chips in the filter core and polypropylene filter capacitors. These components should ensure that the filter produces an authentic sound similar to the original Jupiter-4. He also added an OTA chip in the resonance feedback loop and buffered op-amps to get the appropriated Eurorack levels

On the interface, there are two audio inputs, each with level controls as well. You have frequency & resonance controls, a 3-stage keybed functionality (off, half, full). This is a recreation of the original “Kybd follow” function of the Jupiter-4.

Kybd Follow

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.

Further, you have CV inputs and attenuators for the envelope and LFO inputs which re-creates the J4 modulation options. Unfortunately, there is currently no sound demo for the module. At first look, it is an interesting hand-built module at an affordable price.

The AMSynths AM8104 is available now for £140.

More information here: AMSynths 

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