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Posting this one here vs. C for the verbiage from the manual. It's always interesting to see how manufacturers presented their synths.
"Welcome to the ENSONIQ SQ-80, the first studio synthesizer designed 'for live performance. In a world of synthesizers, sequencers, MIDI controllers and MIDI disk drives, the SQ-80 is something different. It is all of those things and more, in one easy-to-use device. Here's what you get:
• An eight-voice, polyphonic, poly-timbral synthesizer, capable of playing eight different sounds at once, with dynamic stereo panning for each voice.
• Voice section employing state-of-the-art CrossWaveTM synthesis techniques; combine different attack and sustain segments to create a rich variety of complex, dynamic sounds.
• 256k bytes of synthetic, sampled and multi-sampled wavedata in ROM — 75 different Waves.
• Dynamic Voice assignment — each Track/MIDI Channel has access to all eight voices.
• An integrated eight-track MIDI sequencer with 20.000 note capacity and features you would expect to find on stand-alone or computer-based Sequencers.
• A full-featured MIDI controller keyboard capable of sending eight MIDI Program and Volume changes at once.
• Key (Poly) Pressure keyboard — Polyphonic Pressure (or After-touch) affects only the note or notes you press down on, allowing a whole new level of expressiveness. Of course, for sending to instruments which only recognize Mono (or "Channel") Pressure, the SQ-80 can send that too.
• A 3.5" disk drive for fast and reliable storage of up to 600 Sequences and up to 1,728 Programs on a single disk.
• Disk storage for all your MIDI devices —the ability to receive and save to disk any System Exclusive message of up to 64k bytes from any device.
• An eighty-character fluorescent Display and user-friendly "Page-driven" programming scheme to help you keep track of it all.
• Stereo Headphone jack for private listening at home or in the studio.
• Program and Sequence formats which are upwardly compatible with the ENSONIQ ESQ-1, so sounds and sequences created for the ESQ-1 can be played on the SQ-80.
Enough with the verbiage from the manual. What you are getting is a working as new Synthesizer! No broken keys. It comes with 1 Voice Crystal #3."
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-SID2SID: An additional circuit board to add a 2nd SID chip. I have two 8580 sid chips installed. They each have a separate 1/4" output. It gives you 6 voices of polyphony/6 tracks in MSSIAH Sequencer and Drummer apps, as well as mirroring the output from your first SID chip to your second SID chip in MONO and Bassline modes, to give you stereo output. http://www.8bitventures.com/sid2sid/ 
-Feedback Mod: 500k pot. Sid input is grounded when it is turned to the left. Turn it to the right to apply feedback. Will make the sounds much filler and grittier. 
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