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Note the OB-SX is a preset synthesizer with limited real-time controls, however Midisoft makes a plug & play MIDI interface that connects to the computer port on back. The interface gives you
access to extensive parameters. You'll find some demos of it
previously posts here. There is no mention of the port in this listing however there was extensive work done to the unit per the description:

"This vintage Oberheim OBSX 6-Voice Synthesizer is seller refurbished and in excellent condition.
The full story of this classic keyboard can be found here: [
PDF]
Watch this video to hear it for yourself! https://youtu.be/DTakpjc0uYs
The Oberheim OBSX is a RARE keyboard on eBay. It is even more rare to find one that is in such great condition as this one is. I know, because I refurbished this keyboard myself. It took me several months and over $500 in parts, but it was worth it.
Here is a summary of the repairs:
* All NEW wiring except for ribbon cables
* 94 NEW gold-plated Molex connectors (all new board-to-board connections)
* 49 NEW lubricated keboard bushings
* 62 NEW capacitors (mostly electrolytic power supply caps and sample and hold caps)
* 74 NEW ICs (mostly on the control/processor board - all voice card CEMs are original)
* 79 NEW miniature calibration pots
* 12 NEW matched resistors (four each on voice cards #1, #5 and #6)
* One NEW J-wire keyboard contact
* NEW Pitch Bend Pot
* NEW Auto-tune pushbutton and LED
* NEW 8-position DIP switch
* NEW finish hardware on end panels
* Cosmetic paint touch-ups
* Thoroughly cleaned, inside and out (including flux removal)
* Full Calibration
This keyboard is in great condition! Everything works and it sounds and plays like new.
The Oberheim OBSX uses the same Curtis CEM chipset (CEM3340, CEM3320 and CEM3310) used by Oberheim's OB-Xa and OB-8 Analog Synthesizers. These chips were also used in many of the finest analog synths from the 1980s. Their distinctive, fat, analog sound is classic!
This keyboard does not have MIDI capability, although third party MIDI adapters for the OBSX exist. The OBSX was originally designed for use with the Oberheim DSX Sequencer, which allows recording and playback of sequences. (not included in this listing)"