MATRIXSYNTH: Original Rev1 Prophet-10 in Prophet-5 Case

Tuesday, December 18, 2012

Original Rev1 Prophet-10 in Prophet-5 Case

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"This is one of the original Rev1 Prophet 10s in the smaller Prophet 5 size case. This was returned to the factory because of the heating problem where it was converted to a Prophet 5. A tuning upgrade was also installed along with Ver 5.2 Roms. I believe this to be one of the very first Prophet 10's. It has a 2 contact/key keyboard with rubber stops for pressure sensitive keyboard action, along with a motherboard with dual 60 pin connectors for 2 complete voice boards.

Here are some more details on this Prophet.

Lettering on the gray, non silkscreened voice board: Sequential Circuits Model 1000 Board4 Cworks 5-78 R394 V-0

Lettering on the green silkscreened main computer board: Sequential Circuits Model 1000 Board3 R-1 R3 94 V0 Cworks 9-78

A plain paper sticker inside the case: V3.10-051092-0110723-MC

I bought this in 1998 from a person in California in response to an ad (I believe in Nuts and Volts magazine).

I do not remember the persons name or where it was sent from.

The Prophet was advertised as 'not complete' and came with everything Except the metal bottom, back, power supply and serial number plate.

Software is Ver 5.2, with Rom0 and Rom1. This comes with the original Roms plus Rom0 with the startup tune call disabled (currently installed). This lets the synth bypass the tune procedure and immediately start playing, very handy. Press keys 1 and 7 for the normal auto tune.

Since 1998, I have done major overhauls on all 4 boards with many or most IC's replaced along with numerous capacitors and sockets.

The Rev 5.2 software upgrade included aPiggy back board for tuning improvements along with 2 new roms. This upgrade came with the factory conversion from P10 to P5. I found the infernal towering piggyback to be a major cause of trouble and computer lockup, so I remounted the upgrade chips, the 8253 timer and inverter, on the motherboard.

6508 Ram chips were removed, replaced with the much better 6264 Sram (in an unused rom socket) along with a new3V lithium battery life.

I replaced the original ADC chip with a newer ADC0820. Conversion is delayed using 128 wait states for more accuracy, and works perfect.

LED drivers and circuitry from the Ver 3 Prophet was added and also works perfect.
Basically every bit of circuitry on the main control panel has been upgraded or replaced except for the original led display, controls and switches.

All display data latches and associated IC's were replaced. Some push button switches and a couple controls replaced also.

The case is made of the original wood used in those first synthesizers.
A sheet metal bottom was fabricated along with an aluminum back plate which holds a standard computer AC receptacle and a 1/4" output jack. Voltage regulators are mounted on it

This synthesizer works well and starts very quickly. It has the SSM chips. Tuning is bypassed on startup so it turns on almost immediately. The synth can then be tuned as usual with btns 1 and 7.

Much work has been done, electronically and mechanically, to make the system solid and reliable. It powers up flawlessly and runs with very little heating. The synth has a very heavy duty power transformer from a Korg DSS-1 [Update: note the serial number plate on the back] which drew more power than the prophet.There is no overheating and the back heat sink gets only slightly warm.
Some of the original SSM chips have failed, (one SSM2050 ADSR, one SSM2030 VCO, two SSM2040 vcfs)

So to keep it running I added a CEM3340 VCO along with 2 CEM3350 VCF's. I also put a CEM3310 ADSR chip in place of the SSM2050 that quit on voice 3. These all work fairly well except the CEM3340 VCO doesn't want to stay in tune. I include all schematics of these circuits I added along with the control adjustments needed to match these to the circuits they replaced.

This added chips and circuitry can easily be taken out of the synth and the originals put right back in. I basically just put terminals into the empty sockets and wired the new chip to those terminals. A simple instruction tablet explains those circuits in detail, along with how to adjust the controls and how to remove them if you find some originals to put back in.

The slider panel on the left is for sound effects not found with other prophets. The joystick controls normal pitchbend and VCF freq. Slider effects include S/H random note shifts for both VCF's and VCO's as well as fast LFO screams for VCO's and VCF's.
This Prophet is guaranteed to start up and work just fine upon arrival. It will be packaged very carefully with 2 or 3 boxes."

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