rsf Polykobol II Rare French Synthesizer/synthetiseur francais
I was recently contacted by Michael Garcon of saveoursynths.com about possibly working with him to repair a very rare rsf polykobol II synthesizer. At first I was reluctant to get involved, but after reading on the web about rsf and their very ambitious but ill-fated polysynth project, I became interested in learning about it. The polykobol II used either two (version with no sequencer) or three (with sequencer) 6809 CPUs. The front panel had ~153 individual green or red LEDs, plus two 2-digit (7-segment plus dec pt) LED displays. So an impressive total of 185 individual LEDs which could be turned on or off. In addition, there were ~99 front panel switches. Eight voice boards were used, each with two discrete wave-morphing VCO's, a 4-pole SSM filter, a VCA, and two SSM envelope generators, as well as lots of modulation options. An air-filled plastic tube placed under the keys was compressed and the pressure was measured to create an aftertouch value. A Philips minicassette mechanism was mounted on the front panel, and could be used to store and retrieve eight sets of the 48 patches.
As always the first priority was to generate usable schematics of the various circuit boards. Using many high-resolution photos provided by Michael, along with lots of DMM continuity measurements, I have now been able to create fairly complete schematics for the main control board, the key assigner board, the cassette interface board, the voice boards, and the power supply. I also have partial schematics for the AT/LHC PCB, and the three front panel boards (EMB1,EMB2,and EMB3) . All of these need more checking, and there are some gaps that need filling in, but they should already be quite useful. I have also created some test EPROMs for the control and key assigner boards, to help with troubleshooting.
Here are mini versions of several of the new schematics:
I have disassembled the CPU firmware EPROMs for the control board and the key assigner and added many comments to the code. I fixed a bug that was preventing the LFO sync setting from being saved in the patch. I have only seen one set of polykobol II firmware so far. I cannot say if this firmware is compatible with other units. Perhaps their hardware was different.
Here is a sort of "cheat sheet" for operating the PolyKobol II. Some things were discovered by examining the firmware. Some units may have earlier firmware which does not include all of these functions. I did not see a version number in the firmware.
Michael's polykobol II was delivered to its original owner without the sequencer. Apparently the intent was to add it later, but that never happened. So I have no information about the sequencer PCB or firmware.
I would like to collect information (PCB and keybed photos, EPROM dumps, etc) from any other polykobol II's that were made. This will help owners to possibly take advantage of improvements made to later units. Also, I would like to learn how many were delivered with the sequencer and velocity-sensitive keybeds. So if you have a polykobol II, and are interested in some of the documentation that I have created, please contact me.
Michael has installed and is currently using the new MIDI IN interface that I designed for the Polykobol II, which connects to the key assigner PCB of units which do not have the sequencer.
Here is the first prototype pcb:
I am interested in purchasing (or borrowing and repairing) a non-working Polykobol II, so that I can finish drawing out the schematics and possibly design a new key assigner PCB with support for a velocity keybed and with MIDI built-in. No one else seems to be working on any improvements to the Polykobol II design.
Note: Due to the complexity of its design and the details of its construction, the polykobol II is significantly more difficult to work on than most other 1980's polysynths.
Caution: When working on the polykobol II, you should remove the tape from the cassette mechanism. If power is applied with the control ribbon cable unplugged, the tape could be erased, and motor damage may result if a tape is installed.
Please note: Working on a polykobol II requires a lot of skill and care, or damage to the synthesizer could easily result. It should only be attempted by someone with the necessary knowledge, equipment, and experience. I will not be responsible for any damage to any instrument caused by either proper or improper use of the information presented here.