What is it?
This PCB replicates the Ensoniq writeable patch cartridges used by the ESQ-1 and SQ-80 synthesizer released in the 1980s which used 64kb EEPROMs and stored 2 banks of 40 patches each.
Designed with the AT28C64B in mind (28 pin DIP), it can be configured as a read-only or read/write cartridge. Instructions are on the PCB.
Optionally, the AT28C256 EEPROMs can be used with extra components at the top of the board and external switches to provide 4 original carts worth of storage (320 patches).
The schematic designs and CAD files for a 3D printed case will be released under an open source license when I get around to cleaning them up and proving that the 3D design is functional.
Why did you make it?
Both vintage cartridges and many modern, “upgraded” alternatives are now selling for nearly the same price as what owners of these synthesizers originally paid for the entire synth!
A cheaper, more democratized option was required to keep these 36+ year old synthesizers operational and functional.
What makes it special?
This PCB was designed from the ground up based on an original ROM cartridge and publicly available information.
Along with the optional features described above, these PCBs may also help allow intrepid synth hackers to more easily write custom firmware for these 6809-based synths and achieve things that were not originally possible when Ensoniq released them.
Note: After assembly, you have to “initialize” the cartridge before using it. You can do this by saving the synths internal patches to EEPROM. Here are some steps:
Power up the synth
Plug in the cartridge
Press the button under “CARTRIDGE”
Press the button for “INT TO CART A” or “INT TO CART B”
Press the button for “YES”
This includes only the PCB, no components or 3D print housing.