Oberheim Electronics SEM (model CPS-1)

Updated: 2004-10-14

OK, let's face it, the Oberheim SEM (Synthesizer Expander Module) is mainly famous for it's filter and the design of the synth is splendid though quite limited when it comes to architecture and routing. It was released back in 1974 mainly as a MiniMoog expander but soon it became famous as a synth of it's own. The famous filter is a 12 dB one and has been copied many times in other machines since.

Many of the SEMs out there are loose voices from a cannibalised 4-voices or 8-voices. When I decided to try to get myself a SEM I was focusing on "real" SEMs, that is standalone ones. Browsing Ebay I found myself a combined SEM and 360 Systems Slavedriver that had been "roadcased" and some of the case for the SEM was gone. It contained original back panel and PSU though. I won the auction, took the thing to pieces, made a case for the Slavedriver and sold that one (paying for the shipping cost for the entire combo from the US). Left was a SEM with everything, except front, sides and bottom.

I had a huge piece of wood lying around (in fact our old windowsill) that I converted into sides and bottom. I found rubber feet among collected junk (think these belonged to my Simmons TMI originally) and made a patch panel with all available patch points as separate jacks. 

The original design doesn't allow much external patching, but the SEM is designed to be easily expanded with patch field and modifications of your own. The manual even mentions all possible points and where to find the different inputs and outputs. You can use the apropriate Molex connectors or do like I did, simply sold onto the soldering points on the back of the circuit board. Why I did it the "not so nice" way was that one or two of my connectors were already broken.

My patch panel is a cheap construction made out of fake wood and on the front is a laminated, laser printed paper glued to the wood. It works well for this purpose however. A friend helped me to dig out the right font and I tried to cram it together to save space without making it unusable. I choose 6,35 mm jacks instead of the 3,5 mm used on the SEM originally. This to make it easier to interface with other synthsesizers like my MS-20. It's divided into seven sections, one for each oscillator, one for the filter and one for each envelope as well as amplifier and lfo. There were some extra space left so I included some multiple jacks. In every section the jacks on the left are inputs and the ones on the right are outputs.

Here are some more shots of the Wasteland converted SEM of mine... :)

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Oberheim Electronics SEM specifications; 

Keyboard none, standalone unit
Oscillators 2, both with pulse and sawtooth
Noise none, one of the cons
Filter 12 dB/octave, self-oscillating and famous indeed
Envelopes 2, simple ADS
LFO triangle
Connections Standard version: cv in, gate in, moog-gate, lfo out, vca-cntl, low-out, audio in, audio out

Expanded patch panel version: oscillator 1 & 2: cv in, sawtooth out, modulation in, pulse out, sync in, sync out. filter: highpass out, cv in, bandpass out, modulation in, lowpass out, audio in, notch out. envelope 1 & 2: gate in (mislabeled cv), out, trig in. vca: cv in, out. lfo: trig, out. multiple jacks

Housing steel & plastic (standard model), steel & wood (my SEM)
Dimensions 263 x 367 x 175 mm
Weight ? kg
Released 1974
Quantity produced 2000 maybe, more if you count all trashed 4- and 8-voices
Pros Historical, flexible, great interfacing possibilities when expanded. 
Cons Limited when unexpanded, expensive, no noise source.
Price? (bargain,
fair, horrible)
$ 500, 800, 1100

Happy browsing and don't hesitate to drop me a line at: jesperXelectronic-obsession.se

Also please bear in mind that all pictures and texts are mine so, ask before you steal or write your own stuff and take your own pictures! Feel free to link to my pages...