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