the 5 highest keys on my moog source sound weird all of the sudden. they are creating a fluttery(detuned) sound when pressed. They are all fluttering between about a 1/2 step flat and where they should be. Sounds like a loose connection.
Here are a few facts:
when i switch the octave (+1 or 0) it still does it.
when I play a sound with sustain on it the weird fluttering stops after i release the key, and the sustain sounds the way it should sound.
So I figure it’s an issue with the actual key contacts? I believe that most Moogs keys are hooked up in several sections, correct? Any advice is appreciated!
The Source uses a crude successive approximation technique to sense keyboard switch closure. Basically it’s a discrete ADC - the microprocessor generates “pitch voltages” for one input of a comparator while the keyboard CV is in the other input. The “pitch voltages” narrow down from octave, half octave, whole step until the detected note falls between two voltages that are half step and that is the detected note.
Your description doesn’t indicate contact problems, it indicates that those top five notes are on the hairy edge between those half notes and the circuit is flicking between them. There are no “sections” in the Source keyboard circuit.
Trimpot R72 “KYBD SCALE” on the digital board should fix this. Hold high C and tweak R72 until the pitch matches high C with no “flutter”.
It’s actually a neat little detection system, it saves the cost of a (then) expensive ADC IC and makes multiple/single trigger modes a function of software. But it only works for monophonic keyboards with embedded processors.