Here are some pictures of the clone 2-voice board. Currently I’m not making any more of these due to the rarity of many of the IC’s needed.
OB-Mx voice board, PCB layout
The board is powered by an Intel 80C198 CPU, with 32K of ROM and 32K of RAM. It has a single AD7537 DAC that feeds a bank of PD508 sample-and-hold IC’s. These IC’s provide the control voltages to the rest of the analog circuitry: VCA, VCF, pan, and final VCA
There are a number of Xicor E2POT IC’s that are used to trim and calibrate the analog circuitry. They have EEPROM so retain their setting when powered off.
The panning circuitry uses Vactrol analog optoisolators (LED’s optically coupled to photocells) as voltage controlled resistors.
The envelope generators, LFO’s and matrix modulation are all done by the CPU in software and sent to the DAC.
Hi tom
Do you have the typons?
Would you agree to share the work already done?
Luc