Firmware update for later Revision Elka Synthex Synthesizers with MIDI
After designing my MIDI key interface for the first revision of the Elka Synthex, I decided to have a look at the firmware for the later revisions to see if I could make any improvements. This code is contained in three EPROMs. Two are 2532's and one is a 2516. The version of the code I started with is FM3, EU85, and T41. This seems to be the newest Elka code for Synthexes with MIDI. After spending quite a bit of time to understand and comment parts of the code, I made some edits and have created a new version of the firmware. Here are the new features:
1) MIDI CC's are now supported for changing most parameters, with separate control over upper and lower voices.
2) MIDI channel selection is now saved in battery-backed SRAM
3) RAM presets can be saved and restored using MIDI sysex. (All RAM presets are always saved and restored)
4) Sequence RAM can be saved and restored using MIDI sysex. (Entire sequence RAM is always saved and restored)
5) MIDI timing messages no longer affect running status.
The new firmware is contained in a single 27C256 EPROM, and occupies more space than the original three EPROMs provided. To accomplish this, I designed a small pcb to enable using the new EPROM in an un-modified Synthex CPU board. (This firmware will only work in later units with three EPROMs, and installed MIDI) Here is how the board looks after installation:
The board uses three DIP headers to make the connections to the Synthex EPROM sockets. The headers must be aligned perfectly with the sockets to avoid damaging the socket contacts or bending the header pins. The best way to insure proper alignment is to install the headers into the sockets first, and then solder the pcb onto them. I would prefer to offer fully assembled boards which could simply be plugged in, but this is the best way to avoid possible damage to the Synthex EPROM sockets, or bent header pins.
Here is a CC map for the new firmware. Here is information on the sysex file formats, and here are instructions for assembling and installing the board. Please read the installation instructions before ordering.
The code changes have been made carefully, and have been tested by four people so far. There is always a chance that some small bug may turn up, as more people use the new code. If it becomes necessary to send out a new EPROM in a few months, it will be provided at my cost, plus shipping.
Price is $119.95 for a kit with the parts needed to install the new firmware, plus shipping.
This photo shows what is included in the kit. (The EPROM will have a label, of course)
Schematic Issues:
I have found a few mistakes in the service manual schematics. Here is a list.
Please note: The information provided here is not guaranteed to be accurate. I will not be responsible for any damage to synthesizer circuitry caused by its use.