Oberheim SEM Synthesizer Expander Module

the oberheim 4voice also was available from 1 to 8 voices. since 1974 oberheim did these polyphonic synth monster which had a cool filter feature: sweeping from lpf filter to hpf and notch.

2 VCOs and very smooth sound that oberheim stands for.
some audio – a bit sick,but you may have an idea of the sound: SEM_oberheim.mp3
the programmer and voice assign module was for rotating and re-assigning the SEM modules for polyphonic play. you CAN set them to slightly different sounds, but also completely different.. the early 4voice models did not offer the programmer,the shown model is an early model and has 2 sequencers. well. imo thats the better choice because you have s/h ,noise and 2 sequencers in one synth ;)I have seen even mod’ed modular SEM and X-voice e.g. on midiwall.com

think of the new vermona per4mer, that follows some similar concept.. ok, sounds completely different..
pic by/thx to Rob Schweizer (4 voice!)

how to modifiy the SEM modules?

the minisequencer has 2×8 lines to be send to 2 of the SEM modules, as you can see on the assignment switches..

some strange things: since the SEM do only have sine wave as LFO mod you can add S/H (hint: sort of random) to the SEMs alternatively. see „S/H setting

as you can see:
here are 2 mini – sequencers, it’s an early model! later models have the „programmer“ on board ,that allows to „pre program“ SOME of the SEMs parameters.. but not ALL!.. the envelopes are not included in the programmer. butin the 70ies it was of big help for live re-progging 4 and 8 voice synthesizers (note: the programmer offers 16 programs per module)

SEM stands for SYNTHESIZER EXPANDER MODULE, because it was originally made as sort of „expander“ for minimoogs..

in 1974 Tom Oberheim finally put 2 of them together and added the voice assign module and a keyboard: the oberheim 2voice aka TVS-1! the 4 voice was next, and the 8voice followed. some really mad ppl also made a 16voice,but thats not an offizial module ;)

one knob on the SEMs to seamlessly „morph“ from LPF via notch to HPF, the „OFF“ position is BPF. no other synth offers this!! why??

the sequencer is working in the EXT position. it can mod the pw,filters or pitch and also trigger the envs. it also adds noise (white), thats something mostly not mentioned.. ;)

the S/H section also has lag (smothing) and range quite similar to the roland system100 ,sh3 and sh5 models..

well, slow lfos..

SEM alternatives?
ever checked the analogue solutions semblance?

DB quick access:
SEM
2voice
4voice
8voice

the OBERHEIM SEM board

when SEMs & KeyBoard removed..

the mini sequencer of the oberheim – 2 independent SEQ lines and S/H sources to be send to the SEMs in 2 CV „streams“..

the minisequencer board looks like this:



another close look to the emptiness before closing it again..

below: filtermodule (external)

click to enlarge –>