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on Reverb
Update: you can find a link to the schematics and user manual further below.
Only one was previously featured back in 2011 for a MOTM sale
posted here. According to the seller: "Supposedly the WC stands for Wendy Carlos but I have never been able to verify it. i even contacted Stoney the creator of the Slave and he thinks I am correct BUT he can not find the records in his attic."

Auction description: "I purchased this Slave in 1998. I was not even aware they existed until reading Mark Vail's book 'Vintage Synthesizers'. I am sure that book is what infected a lot of us with the vintage synth BUG.
This is like a rack mount Synergy with more features. You can control the velocity, pitch, and modulation from any vintage or modern midi controller.
The internal board is marked 002 and the hand written serial number has faded or been accidentally wiped off with a misguided spritz of contact cleaner but it also reads 002. The synth is in overall good, un-abused shape with no bent rack ears etc. It does have some very mild rack rash here and there in the typical places but overall it is very clean.