SCI Prophet Remote "Keytar"

Update: 03/01/2026

Sequential Circuits (aka SCI) back in 1980 was riding high on the success of the Prophet 5 polyphonic analog synthesizer. The Prophet went through several firmware and circuit revisions. When one of their last revisions was released in 1981, they introduced the optional polyphonic sequencer and Remote controller. The model 1001 Remote is a keyboard designed as a remote "keytar" controller for the Prophet-5, and it only works with a rev 3.2 or 3.3 model. Earlier Prophet-5 revisions cannot be retrofitted to use the Remote because the processor circuit board does not have the support circuits.

The Remote was not a MIDI controller; about 300 of them were made before production of the Prophet-5 ended. SCI had never developed a proper MIDI implementation for the Prophet-5 or Prophet-10. A 20 foot hefty interface cable connected the Remote to a Prophet-5 (an optional 40 foot cable was available). The 49 note keyboard was not velocity sensitive, three modulation wheels were provided (the pitch wheel is spring loaded but unipolar only bends up), and there were buttons to select any of 40 programs on the Prophet-5 (on a model with 120 programs, you still only had access to the first 40). The 3rd wheel was labeled AUX.

This one showed up on an auction site and I won the item as the only bidder. I do not own a Prophet-5. So why did I buy it?

I intend to remove the original circuit board and shoehorn a MIDI retrofit.
It's a nice low profile controller that sits neatly on top of my Hammond XK3 in my stage rig.
I'm not sure that I can revive my broken Lync LN1000 Keytar, so this will be an easier project.
Almost every other "keytar" product is uncool. They look nerdy and I refused to be seen with them.
Almost every other "keytar" product includes on-board sounds, which I do not want. I only want a MIDI controller that will control sounds I have already developed.
Most "keytar" keyboards are too short. A 49 note keyboard is the minimum I will use.
I like the feel of the old Pratt-Read keybeds on 1970s and 1980s synths. I never liked the feather light feel of modern keybeds.

The Remote used both the rear panel digital jack and analog jack on the rev 3.2 & 3.3 Prophet-5, and there is a hefty 10 pin connector at the Remote end. This all pre-dated MIDI. The analog jack provided power to the Remote, and received the CVs from the mod and pitch bend wheels. The digital jack was the digital interface for key data and program select - this used the USART on the Prophet-5. The AUX wheel terminates at a 1/4" TS plug, where it could plug into either the rear panel filter jack (filter sweep) or amplifier jack (volume control). That hefty cable carried digital signals, analog CVs, and power rails.

An EPROM loaded Intel 8748 microcomputer receives system clock and serial data from the Prophet-5, handles scanning the keyboard and program buttons, and transmits serial data. While the Remote is a 49 note keyboard, the schematic reveals provision for a five octave 61 note keyboard. Maybe this was an option on the drawing board but was never produced. Reviewing the format of the serial data, it is not far from what would become MIDI. The difference is that the Remote constantly sends serial keyboard data, rather than only when an event change occurs. Also while MIDI digital I/O is a current loop, the Remote I/O is a single wire voltage domain. The advantage of a current loop is that it does not require a ground reference, which eliminates ground loops.

On its own, the Remote is useless without a Prophet-5. The original circuit board is not suitable to convert to MIDI operation. Reprogramming the 8748 is not a great proposition in that development systems are no longer available, and 8748 compiler software options are limited. I'm not sure if the security bit is asserted on the 8748, which prevents reading or writing the EPROM space (although this 8748 does have the window for erasing the EPROM). I have some Intel 87xx databooks stored in the garage, there might be info there. The 8748 has no analog voltage inputs, so the wheels cannot be interfaced.

So I intend to remove the original circuit board and retrofit a Highly Liquid MIDI-CPU MIDI interface (sadly no longer made) for the keyboard and the wheels. I'm not sure if the switches can be implemented with the retrofit, I have to study the Highly Liquid document some more. I don't need provisions to change the MIDI channel or transpose, that's what my JL Cooper MSB+ is for. Ditto with MIDI program change, that's what my Kurzweil MIDIBoard is for.

I was successful with a similar retrofit on my Moog Taurus II bass pedals. At the moment this project is not a priority, so check back later for updates!

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