prophet 52

Sequential Circuits Prophet-5

Sequential Circuits Prophet-52 (the '5' with chorus)

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Sequential circuits released amongst the first truly polyphonic synthesisers

where a group of voice circuits (5 in this case) were linked to an onboard

computer that gave the same parameters to each voice and drove the notes to

each voice from the keyboard. The device had some limited memories to allow

for real live stage work. The synth was amazingly flexible regaring the

oscillator options and modulation routing, producing some of the fattest

sounds around. They also had some of the fattest pricing as well, putting it

out of reach of all but the select few, something that maintained its mythical

status. David Sylvian of Duran Duran used the synth to wide acclaim in the

early 80's as did many of the new wave of bands.

The -52 is the same as the -5 with the addition of a chorus as it was easy, it

turns the synth stereo for more width to the sound, and others have done it on

the Win platform.

The design of the Prophet synthesisers follows that of the Mini Moog. It has

three oscillators one of them as a dedicated LFO. The second audio oscillator

can also function as a second LFO, and can cross modulate oscillator A for FM

type effects. The audible oscillators have fixed waveforms with pulse width

modulation of the square wave. These are then mixed and sent to the filter with

two envelopes, for the filter and amplifier.

Modulation bussing is quite rich. There is the wheel modulation which is global,

taking the LFO and Noise as a mixed source, and send it under wheel control to

any of the oscillator frequency and pulse width, plus the filter cutoff. Poly

mods take two sources, the filter envelope and Osc-B output (which are fully

polyphonic, or rather, independent per voice), and can route them through to

Osc-A frequency and Pulse Width, or through to the filter. To get the filter

envelope to actually affect the filter it needs to go through the PolyMod

section. Directing the filter envelope to the PW of Osc-A can make wide, breathy

scanning effects, and when applied to the frequency can give portamento effects.

LFO:

Frequency: 0.1 to 50 Hz

Shape: Ramp/Triangle/Square. All can be selected, none selected should

give a sine wave (*)

(*) Not yet implemented.

Wheel Mod:

Mix: LFO/Noise

Dest: Osc-A Freq/Osc-B Freq/Osc-A PW/Osc-B PW/Filter Cutoff

Poly Mod: These are affected by key velocity.

Filter Env: Amount of filter envelope applied

Osc-B: Amount of Osc-B applied:

Dest: Osc-A Freq/Osc-A PW/Filter Cutoff

Osc-A:

Freq: 32' to 1' in octave steps

Shape: Ramp or Square

Pulse Width: only when Square is active.

Sync: synchronise to Osc-B

Osc-B:

Freq: 32' to 1' in octave steps

Fine: +/- 7 semitones

Shape: Ramp/Triangle/Square

Pulse Width: only when Square is active.

LFO: Lowers frequency by 'several' octaves.

KBD: enable/disable keyboard tracking.

Mixer:

Gain for Osc-A, Osc-B, Noise

Filter:

Cutoff: cuttof frequency

Res: Resonance/Q/Emphasis

Env: amount of PolyMod affecting to cutoff.

Envelopes: One each for PolyMod (filter) and amplifier.

Attack

Decay

Sustain

Release

Global:

Master Volume

A440 - stable sine wave at A440 Hz for tuning.

Midi: channel up/down

Release: release all notes

Tune: autotune oscillators.

Glide: amount of portamento

Unison: gang all voices to a single 'fat' monophonic synthesiser.

This is one of the fatter of the Bristol synths and the design of the mods

is impressive (not my design, this is as per sequential circuits spec). Some

of the cross modulations are noisy, notably 'Osc-B->Freq Osc-A' for square

waves as dest and worse as source.

The chorus used by the Prophet-52 is a stereo 'Dimension-D' type effect. The

signal is panned from left to right at one rate, and the phasing and depth at

a separate rate to generate subtle chorus through to helicopter flanging.

Memories are loaded by selecting the 'Bank' button and typing in a two digit

bank number followed by load. Once the bank has been selected then 8 memories

from the bank can be loaded by pressing another memory select and pressing

load. The display will show free memories (FRE) or programmed (PRG).