JP04 Analog Modular Synthesizer

Overview The AMSynths JP04 Analog Modular Synthesizer is a set of five Euro Rack modules that together with a 84HP Euro Rack case such as the Roland SYR-E84 create a dual VCO, single voice replica of the Jupiter 4 and Pro Mars from 1978. More modules can be added to create more voices, perhaps controlled by a MIDI to 4 voice CV/gate module.mixer.

There are five modules that have a total width of 104 HP and an internal PCB.

  • AM8410 LFO’s
  • AM8400 VCO-1
  • AM8400 VCO-2
  • AM8104 VCF
  • AM8108 Dual ADSR & VCA

The JP04 provides the flexibility of a modular synthesizer based on a traditional 1978 analog synthesizer, with the addition of 3.5mm cable patching to either recreate the original signal flow or to create new internal an external connectivity.

Cabinet and Power I have used a Roland SYR-E84 case for my JP04 modules, which is expensive but very good quality. I removed the ribbon power cables as they are an absolute pain to use! Instead I have fitted a power bus into my Ensemble PCB which then uses normal power cables to each of the modules.

Chorus Ensemble  The Jupiter-4 had a dual channel BBD chorus to enrich the sound of a single VCO voice. I have recreated this using the original MN3004 BBD chips, and designed a PCB that fits into the bottom of the case. It also has a power bus on the PCB as well with the CV and Gate lines connected to external jack sockets at the rear, for seamless connection to a keyboard or MIDI module.

Normalisation The JP04 modules have been normalised to a common modulation CV range of 0V to +7.5V, which means all the CV generators create signals in this range and all the modulation and envelope inputs of the VCO’s, VCF and VCA are at maximum depth at +7.5V. The gate inputs are all set for 0 to +5V operation, and the S&H will generate trigger signals of oV to +10V.

Documentation All the modules come with a high quality printed JP04 Quick Start Manual that explains the functionality of each module, and how the five modules and ensemble PCB can be used as a complete analog synthesizer.

We also provide a set of hard copy and online blank patch sheets, as well as the JP04 Synthesizer Patch Book which contains patches created on the Jupiter 4.


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