The Programmer

A special module of the four voice is its programmer. It allows to set up various parameters and store them into an internal memory with 16 places, separately for each SEM.
It also features two ADS envelope generators for the SEM’s VCA and for modulating the VCF.

The parameters are:

  • frequency setting (offset to other sources) for both VCOs and the VCF
  • A-D-S for both envelope generators
  • Frequency of an internal LFO, individual to each SEM (called “vibrato”)
  • Amount of LFO to OSCs (1+2 simultaneously)
  • Amount of 2nd envelope to VCF frequency (called “modulation”)

The voltages are converted by a 6 bit A/D converter and then into a bit stream to be either stored into 2 1024 bit SRAMs or bypassed around the memory in manual setting. Due to this, testing and troubleshooting of most parts of the circuits is possible in real time.

Every of the 2 channel boards of the programmer features 4 proprietary envelope generator ICs which are said to be a predecessor of the famous CEM 3310. It is far away from being compatible though, and the custom Oberheim ICs also have an additional VCA integated to the envelope chip.

This photo shows the programmer stacked together, with the channel 3&4 board on top. Some CMOS ICs as well as several LM324 had to be replaced here. The cermet presets are kept in place, while the rarely used carbon track presets are to be replaced.

One potentiometer on the programmer’s front panel unfortunately had a severe crack in the resistive track, so I had to mix up parts of the original potentiometer with the track of a brand new 24mm Alpha brand pot.

A set of new T1 3/4 light bulbs completed the programmer.