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Tom Oberheim SEM-Pro

Tom Oberheim SEM-Pro front view

This is Synthesizer Expander Module is the 2009 version of the 1974 SEM-1. It combines most patch points of the SEM Patch Panel version and the SEM MIDI to CV features in one housing. It was produced in lower numbers from 2011 on. It got Tom Oberheim's signature on the vertical front.
The housing is steady metal. The concentric axis of the VCO course and fine tuning of the original 70ies version were not used in this reincarnation. There is a course tuning knob about the size of the original version. The fine tuning is a black pot axis to the top right of the course tuning knob. I guess, starting to get a low number of these concentric double pot was just too expensive or simply unavailable to source. The full CCW switch of the filter mode pot is changed to a switch below the pot. All these changes are minor and should not effect the sound or the handling of this synth.

As Tom Oberheim was not allowed to use his own name due to the lost of the trademark rights for "Oberheim", he had his company named Marion System Cooperation ("Marion" is the first name of his wife). But he used bold letters to emphase his domain name Later Tom Oberheim was given back his trademark of his family name by Behringer, the last owner of this trademark.

The original SEM-1 was not the result of just Tom's sole work. While he set the feature set and the user interface. Jim Cooper (if you were into synth in the early eighties, you know his name) designed the circuity. Dave Rossum (of E-mu and SSM) helped with the VCO design. Dennis Colin of ARP designed the multimode filter.[1]

Tom Oberheim SEM-Pro back view

While the MIDI to CV part let you route either MIDI CC, velocity or (monophonic) aftertouch to the filter, pitch or VCA, it is not possible to route the modwheel of a MIDI controller like a keyboard to the LFO modulation amount. But you may use the modwheel CC to change the filter cutoff.

There is last, high and low note assignment (= note priority) modes on the MIDI to CV panel. And while last note priority is selected, you may switch retriggering the envelopes with each new key played on or off. The later gives allows you to bind notes by playing legato without restarting the envelope. In the other note priorities it is always defaults no retriggering (= single trigger). So the setting of low note priority is the way a original Minimoog works. You have to let all keys go before you are able to change the note priority.

If you don't us the external audio in #2 socket, turning up the EXT #2 volume gives you a 440 Hz note A tuning reference tone. This is very handy to tune the oszillators, if you use the course frequency knob for setting the oscillators to different octaves (as there is no footage switch for the oscillators). For transposing both oszillators to different octaves, there is a +2 to -2 Octaves transpose on the MIDI to CV panel.

The backside connections are, except of the MIDI sockets and the power socket (24 V DC, 300 mA negativ on the outside), are 6.35 mm (1/4") in size. The one of the top rim of the panel are all 3.5 mm (1/8").

[1]: from "Manual for the Synthesizer Expander Module 'MIDI to CV' version"; Chapter 10: "History of the SEM"