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Sunday, December 10th, 2023 06:37 am

Synth Glossary

An envelope generator generates a signal that changes through the length of a sound, normally to control the loudness of that sound. An example of its use is to control the volume of a piano sound. It creates a signal that goes from low to high very quickly (the loud bit when the key is pressed), then goes down slowly as the sounds gets quieter. They are also used to drive other parts of the synthesizer, for example the filter....


Version 1

The original Prophet-10 was released in 1978. I was simply a 10-voice version of the Prophet-5. It was identical to the Prophet-5 (revision 1) on the outside and on the inside, with the exception of the hardware for the extra voices. However, it had a problem with over-heating. The Rev. 1 Prophet-5's were unstable and susceptible to heat as it was. Adding the hardware and resulting heat of 5 more voices was just too much. Many of these Prophet-10's were recalled, half of their voice cards ripped out and changed into Prophet-5's.

Version 2
The Prophet-10 was once again attempted in 1979, this time in a larger chassis and with a double-manual keyboard, both 5-octaves, 1-note (C-C). This Prophet-10, like the Rev. 2 Prophet-5 was designed around the SSM chips. These SSM chips, though they sounded good, were a bit unreliable (hence the problems with the early Prophet-5's). After the first three prototypes were made, sequential decided to drop the SSM chips and switch to Curtis (CEM) chips, which were reported to be more stable. They were also reported to not sound as good as the SSM chips, but so goes the history of synthesis. Those three Prophet 10's have become something of a legend. If they exist, they are some of the most desirable of all Sequential Circuits products.

Version 3
Finally, in 1980 a working 10-voice, 20-oscillator, double-manual keyboard, Prophet-10 made it into production. One of the largest analog synths available at the time, the Prophet-10 featured much of the same architecture as the Rev. 3 Prophet-5. Like the Prophet-5, each voice consisted of two VCO's (voltage controlled oscillators) and a white noise source, all of which can be mixed into a resonant low-pass VCF (voltage controlled filter). The filter modifies the voice timbre under control of its four-stage envelope generator. The filter may also be resonated and serve as a sound source. Following each filter, a VCA (voltage controlled amplifier), also controlled by a four-stage envelope generator, shapes the voice amplitude. Supplementing the basic voices are polyphonic modulation (POLY-MOD) signal routings within each voice that allow VCO2 and the filter envelope generator to function as modulation sources applied to VCO1 frequency, pulse width, or the filter frequency. Finally, there is a single LFO (low- frequency oscillator) and a pink noise source which can be mixed to modulate all voices, as adjusted by the MOD wheel. All of the voice settings, along with settings for volume and tuning, could be saved and instantly recalled on a total of 32 memory locations (4 banks of 8). Some early Prophet-10's were recalled because of problems with memory loss. For this, Sequential performed what they affectionately called the "Ugly Mod", which reportedly fixed the problem.

The Prophet-5 features two complete sets of program switches with corresponding LEDs that light up to show you which voice is playing. To the right of the program switches are the master volume knobs and tuning aids, including an A-440 tone module, a master tune knob, and the autotune button. To the right of what otherwise looks much like a Prophet-5 front panel is an extra section. Here are the programmable volume and tuning knobs, and switches for routing the input from two available footpedals. Destinations are pitch, cut-off, VCA, or mono modulation. As in the Prophet-5, there is also a release switch.

Above the two groups of program selector switches are the keyboard mode switches. The two keyboards can be configured to the following modes:

Normal Mode - This mode set the Prophet-10 up with two separate 5-voice polyphonic keyboards.

Single - This mode created a 10-voice polyphonic instrument which could be played on either or both keyboards.

Double - This mode creates a 5-note polyphonic layered sound using both patches. This 4-VCO sound can be played on either or both keyboards.

Alternate - This mode alternates between the two patches selected. One note would be the first patch and the next note played, on either keyboard, will be the second patch.

On the back of the Prophet-10 are two sets of outputs, three XLR (balanced) outputs and a three 1/4" jack outputs. The three outputs correspond to Left, Right, and Mono. Also on the back are two CV (Control Voltage) pedal inputs, and a little matrix of four jack sockets for CV and gate outputs (with last note priority), CV and trigger in (for voice 5 on the upper keyboard), and switch sockets for release, program increments, and sequencer control. The Sequencer on the Prophet-10 was optional. It could be installed in the factory before the unit was shipped or it could be retro-fitted at a later date.

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