AMSynths AM8400 JP04 VCO, the Roland Jupiter-4 oscillator for Eurorack

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AMSynths has pulled the characterful VCO section of the legendary Roland Jupiter-4 in a new Eurorack module (AM8400 JP04 VCO)

The British Synthesizer developer Rob Keeble is a specialist in the field of cloning. In addition to his numerous vintage synth circuit replicas for Eurorack, he collaborated with Behringer on many projects. Among other things, the excellent 2600 Synthesizer or the new 2500 modules. They are currently working on the Roland SH-5 replica, which we can be very excited about.

Things are going on in his company AMSynths too. He recently released the AM8104, a replica of the filter circuit of the Roland Jupiter-4 from 1978 in Eurorack. The AM8400 module now also brings back the VCO of this famous vintage synth.

AMSynths AM8400 VCO

AMSynths AM8400 VCO

The original Jupiter-4 oscillator is special to this day because of its unique character and circuit. It uses a 555 timer chip and a CMOS divider chip to create square waves which are then shaped into sawtooth and pulses.

According to AMSynths, they use the same complements to be as close as possible to the original VCO but with one exception. It uses a new Tempco based matched transistor pair instead of the obsolete heated uA726 chip, as the exponential generator. This gives you better warm-up time and precision.

The AM8400 VCO has all the original features. Starting with the pitch that ranges from 32′ to 2s, adjustable with the dedicated pitch and range knobs. Saw, square, and pulse waveforms are available as main waveforms. Plus, you get a sub-oscillator with an on/off switch that adds a square wave one octave below the VCO frequency. Nice, if you turn the waveform off, you can only hear the sub-oscillator. Then, you get pulse width modulation with manual & external control as well as FM depth.

Interesting, there is no 1V/oct input on the interface. The VCO derives its frequency from the Doepfer keyboard bus which is in the power cable. Alternatively, you can use the MOD input that has a 1V/octave calibration with the slider at maximum.

At this point, there is no sound demo of the VCO.  Nonetheless, it’s nice to see that you can now get the Jupiter-4 VCO next to the VCF (AM8104 JP04 VCF) as a replica in Eurorack at a very fair price. The Jupiter

The AMSynths AM8400 VCO is available now for £150 from the official store.  It’s currently sold out (article release day).

More information here: AMSynths 

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