SDSV oscillator 'bleed'?
2019-04-20 by tubmyk2@...
Hey guys, question - I'm in the process of revamping my SDSV, which so far entailed a power supply recap and 110v transformer conversion. This eliminated about 99.9% of the noise, hum and buzz I was getting through the unit on top of using the step-down transformer.
Now that it's so quiet, I notice that as I turn the tone clockwise on a module (pretty sure all modules will do it), the higher the pitch gets it will bleed through and be audible. Looking at the schematic I can't figure out where the oscillator circuit is, but I do know that I was probing around one of the op amps (IC17, MC1458) and the components immediately surrounding it, and as I probed the different pins I would get a tone change. I'm not sure what to look for on the scope, as I imagine this is all functioning correctly and 2 different cards that I've examined so far have done the same thing.
Has anyone else noticed this? This was happening before the voltage conversion, now that I think about it, because I recall you could set the tone a little higher and there was always a little audible tone bleeding through.
I would love some guidance on this but I know it's a shot in the dark as it probably is by design....