MATRIXSYNTH: Sequential Circuits Prophet~600 | By Design

Thursday, November 21, 2019

Sequential Circuits Prophet~600 | By Design


Published on Nov 21, 2019 Alex Ball

"Another synth demo, this time with the Sequential Circuits Prophet~600 buddied up with its siblings.

This synth was the very first instrument released with midi (with Dave Smith of Sequential being the "father of midi"). He was later awarded a Grammy for its invention along with Ikataro Kakehashi of Roland. It was famously hooked up to a Roland Jupiter-6 at the Winter NAMM of 1983 to demonstrate that a universal protocol had been achieved.

The Prophet~600 was the third of this iconic series to be released after the Prophet~5 (1978) and Prophet~10 (1980). With their eye on affordable poly synths such as the Kory Polysix and Roland Juno-60, Sequential looked to create a cutdown version of their earlier Prophets and the 600 was the result. Around 6,000 of them were made between 1983 - 1985.

It has 6-voice polyphony with two oscillators per voice and has mixable saw, triangle and pulse available on both of those oscillators. The VCOs are identical to those found in the Prophet~5 rev3, Pro~One and Prophet~10 but the other ICs are different.

It has a resonant low pass filter, two envelopes, an LFO, poly mod, glide, oscillator sync, unison mode, patch memory, an arpeggiator and two sequencers.

And here's where things get interesting: the 600 has digitally generated envelope, LFO and glide voltages as well as digital values for the switches and potentiometers. In order to keep the cost down, an 8-bit Z80 processor and DAC were used that didn't quite have the spec to perform these functions at the speed or with the resolution that was ideal (it was 1983 after all). The result was that the envelopes weren't snappy enough and when sweeping the filter you can hear it stepping through the values.

Most owners rectify this and unlock the potential of the 600 with the GliGli mod that replaces the old processor with a modern one and also adds a bunch of features and the unit I'm using has this upgrade. We now have increased resolution, extra LFO modes, multimode envelope generation, unison detune, noise source, mix overdrive, full midi implementation and more.

In terms of physical changes, the oscillator mix potentiometer is now the Oscillator A level and the portamento the Oscillator B level. The envelope amount is now bi-polar with level 5 being the 0 volt point. The other updates are accessed via the numeric pad and speed dial whilst in manual mode.

I made all the sounds in manual mode and also used some timed automation of various parameters in places via midi.

Instruments used:
Sequential Circuits Prophet~600 (1983)
Sequential Circuits Pro~One (1981)
Sequential Circuits Drumtraks (1984)
Ibanez Jem 7DBK (2002)
Fender Blues Junior II mic'd with an SM57
Boss CE-2 (1979)"

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