Oberheim SEM

Oberheim SEM Image

The SEM was Oberheim's first official analog synthesizer. SEM stands for Synthesizer Expander Module. It was conceived with the notion of being used as a backup synth connected to a sequencer for layering or beefing up your existing monophonic analog synths. The SEM itself was a keyboard-less module with two analog oscillators, a 2-pole multimode filter, ADR envelopes, and an LFO. Each of the two oscillators offer triangle or rectangular waveforms. But unlike the Moog and ARP counterparts of the time, the SEM's 2-pole (12dB/oct) filter was a little thin. The others used a 4-pole (24dB/oct) filter which has a steeper roll-off and so it sounds much better. But the SEM's filter offered many modes in addition to low-pass, including high-pass, band-pass and band-reject.

Although SEM modules and other external controllers could be inter-connected, the SEM is not a patchable synth module like other modular type synths of the time. Its signal routing was more or less, hard-wired. The SEM was for all purposes, an accessory. But Oberheim jumped into the synth market by coupling SEMs with a keyboard and an analog sequencer into a compact, white, little performance synth. That led to the Two Voice, Four Voice and Eight Voice models. And from there, came the rest of Oberheim's history of instruments. Some earlier SEMs have several differences in their circuit design that affects the envelopes, filter, etc. If your SEM has "1080" written inside, it's an early one. If you see "1180", it's the "normal" one that most people know and love.

Oberheim SEM Image

Pictured just above is the Polyphonic Synthesizer Programmer, introduced in 1976. It could be used with the SEM and the Two-, Four-, and Eight-Voice models. The unique feature this programmer had (for its time) was the ability to store the knob settings of a SEM modules parameters. Neither Moog nor ARP could offer memory/patch storage like this at the time. The PSP could accommodate up to 8 SEMs or, in other words, the Eight Voice. SEMs have been used by Jan Hammer, Josef Zawinul, and filmaker/composer John Carpenter.

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17 Visitor comments
December 24, 2010 @ 10:23 pm
This simple synth has an ever-growing sweet spot in the mids. In it for the tone!
August 26, 2010 @ 7:26 am
Did I read "thin filter" somewhere above? No way. The "thinness" of the SEM filters is one of those ideas people are passing along without ever really listening to one, just quoting reviews of revies. I had never used a SEM, I always used the OBs. Recently, I finally bought a vintage SEM, in search for "more" of the OB's smooth sound... and I was surprised when it started releasing punching and snappy basses. My fat bottom in thinner that this baby.
July 1, 2010 @ 10:20 am
An addition to the "used by list" is Larry Fast/Synergy. I'm listening to _Electronic Realizations . . ._ right now and had to look this one up!
February 12, 2010 @ 12:11 am
i never thought of it as being thin. more harmonic in the mids. more aggressive. i wish i never sold my SEM. i will buy a new one as soon as they are in stock. Still have an OB1 which has a selectable 12db and 24db and a minimoog with a 24db. the 12db is my fav. but i guess it's all a matter of taste
November 15, 2009 @ 10:16 pm
Just got the tom oberheim patch panel SEM and it sounds unbelieveable! The 12 db/oct filter isn't thin as stated above so don’t let that scare you away. What’s unique about it is the LP/Notch/HP filters are sweepable so you get all the tone colors in between, in addition to the cutoff and resonance knobs. The patch panel lets you have 3 VCOs by taking the saw/square wave out of VCO 1 or 2 and routing it to the external input which really fattens it up just like on a minimoog. The sound is right up there with my minimoog or pro-one. I also have a Jupiter 6/8 and a Prophet 5 and they’re not even close.
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  • The link above will take you to an eBay search for this synth to see active listings. If you don't find it there, try looking in our forum marketplace or post a wanted classified.
  • Specifications
  • Polyphony - Monophonic
  • Oscillators - 2 VCO's (each with sawtooth or variable-pulse waveforms)
  • LFO - LFO is triangle wave only
  • Filter - 2-pole multimode (low-, band-, hi-pass, band-reject) VCF with ASR (Attack, Decay and Sustain) generator
  • VCA - 2 ADR (Attack, Decay and Sustain) Envelope Generators
  • Keyboard - None
  • Effects - None
  • Memory - Not on-board. External Polyphonic Synthesizer Programmer module stores control voltage settings for up to 8 SEM modules each.
  • Arpeg/Seq - Not on-board. External DS-2 Digital Sequencer option.
  • Control - CV / Gate
  • Date Produced - 1974 - 1979

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