Product Code: AM8400PCB
Product Description
This is set of 2x PCB's to build a replica of the VCO in the Roland Jupiter 4 polyphonic synthesizer introduced in 1978. The Jupiter 4 is famous for its powerful sounds and efficient controls.

Euro Rack Module: 14HP wide
Project Build:         Download PDF

The AMSynths circuit is very close to the original except for a new Tempco based matched transistor pair rather than the obsolete heated uA726 chip, as the exponential generator. Original components have been used (like the DN819), along with a few careful upgrades:

  • 1% Polystyrene Capacitors
  • LS312 Matched Transistor Pair
  • Precision 10V reference

The panel design keeps close to the original with a rather sparse set of controls; Range from 2' to 32', a choice of three wave forms (off, triangle, square, pulse), a modulation depth slide, a pulse width selection switch from manual to active modulation, a four way switch for modulation amount and a sub oscillator on/off. The VCO can be used standalone, or in pairs like the ProMars using the Doepfer bus, or four VCO's can be used with a MIDI to polyphonic converter for the full Jupiter 4 sound.

There are just three 3.5 mm jack sockets on the base of the front panel:

  • Keyboard Input (defaults to Doepfer bus)
  • Modulation input
  • Audio output




£15.00 inc. tax
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Product Details
Brand: AMSynths
weight: 300g
Product Condition: New
Product Description
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