Roland Jupiter-4

Roland Jupiter-4
Roland Jupiter-4 Compuphonic
Manufacturer	Roland
Dates	1978 - 1981
Price	US$2,895 UK£1,810 JP¥385,000
Technical specifications
Polyphony	4 voices
Timbrality	Monotimbral
Oscillator	1 VCO + 1 sub-oscillator per voice
LFO	1 triangle/square/sawtooth/reverse sawtooth
Synthesis type	Analog Subtractive
Filter	1 resonant lowpass, 1 highpass
Attenuator	2 ADSR
Aftertouch expression	No
Velocity expression	No
Storage memory	10 presets/8 user patches
Effects	chorus
Input/output
Keyboard	49 keys
External control	None

The Roland Jupiter-4 (JP-4) was an analog synthesizer manufactured by the Roland Corporation between 1978 and 1981. It was notable as the company's first self-contained polyphonic synthesizer, and for containing digital control of analog circuits (termed "Compuphonic" by Roland), allowing for such features as programmable memories and voice assignment modes.

Priced at US$2,895, it was cheaper than polyphonic machines from its competitors (such as the Sequential Circuits Prophet-5 and the Oberheim OB-X). However, it did not sell well in comparison. (These poor fortunes were reversed on the release of its successor model in 1981, the popular Jupiter-8.)

The Jupiter-4's basic architecture consisted of four identical voice cards, each with a VCO (and sub-oscillator), resonant low pass VCF (Roland BA662 in earlier revisions or IR3109 in later models IC, which could self-oscillate), and variable-gain amplifier (VCA). Modulation included an Attack-Decay-Sustain-Release (ADSR) envelope for the filter, and another for the voltage-control amplifier and a final level output with an overload LED, as well as a separate unmemorized master volume control. The filter ADSR could be inverted, allowing for "upside down" modulation. The final VCA level setting could be memorized in user presets, and was prior to the overall master stereo output volume. The LFO, routable to oscillator pitch, pulse width, filter cutoff and amplifier, was notable for being able to reach audio frequencies, allowing for crude FM and AM synthesis. Those settings were memorized in the user presets but a fully adjustable depth remained independently configurable through the pitch wheel to combinations of VCO, VCF and VCA, as well as a bend range. The VCOs can garner unstable tuning if aging or low-quality electrolytic capacitors are used (two for each voice card). Synthesizer repair shops can replace these tuning capacitors with stable polystyrene capacitors for an instant perfect tune. Individual oscillator card VCO tuning is accessed by four capped holes in the middle of the back of the case, but the unit should be allowed to warm up before adjusting for at least 20 to 40 minutes prior to adjustment.