The original portable subtractive analog monosynth with built in keyboard. A lot of innovative discrete circuits that have become building blocks for many other synths.
Tunings will drift some on warm up of course and the machines should be tuned in conditions they will be used mostly in. Many problems are solved by just carefully following the calibration proceedures.
Many of the parts used in these machines are common and in my stock. Fred McNiff I believe has the uA726 transistor pair.
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