Those extra sockets on the osc board could be for the EML Poly-box. That used a small keyboard with some type of memory, instead of the switches found on the SynKey.
In a letter from EML president Dale Blake dated Oct.18,1977:
"The Synkey oscillator is available seperatly for $105 including the pushbuttons and nessessary pots. It operates from +-15 volts and the output about +-5volts. The oscillator has a linear response - ie. its frequency is proportional to voltage. It may be combined with the Exponential Amplifier/Mixer to give 1 octave per volt response required if you are running it from a keyboard voltage.
Polybox is a pitch following version with additional features. In polybox the pitch selection is from the keyboard rather than with the buttons."
For those not familiar with EML, they offered many DIY boards like the Expo Amp/Mixer that Dale is reffering to. I still have a few around, but never took Dale up on his offer for the Synkey oscillator board.
Automatic Gainsay wrote:That's cool! That modulation (sample-and-hold with waveform input instead of noise) is a really cool effect. It sounds like the sample and hold on the Roland SH-3a. That effect over the divide-down chords is REALLY cool!
Com'on AG! I can think of another synth that does chords with a very similar S&H with ramp waveform. Although I never did thank the guy that did the videos on that synth. Can't remember the model, a PS something or other?
But yeah, that Synkey was a cool synth. Didn't that have after touch?
Thanks B00gie for the pics and the great demo, brings back memories.