Yes, the resonance knob on the 490 is "very touchy". Mine started to self-oscillate at around 3.5 ticks. The manual suggests changing R39 to 51K to 68K. I had both, and went with 51.1K At the high end it starts to oscillate at a resonance setting of about 4.5. With the frequency knob in the middle, it starts around 6. It begins to oscillate around 8.5. at the low end (around 90Hz). Is there any way to get it to self-oscillate below that?? The 440 goes down to around 20Hz. Does it sound like a Moog?? While I can't do an AB comparison, it certainly exhibits the safe goofy response to FM modulation, so I'm happy :) I don't know if it does the rising cutoff thing -- it's very hard to tell misusing a 320 as a VCO (the 320 overshoots with quick CV changes). Also, in an attempt to minimize gratuitous drift, I pushed the two transistors together with a bit of heat sink, and cinched them together with a wire tie. Now if certain people want to call me names because that's what makes a Moog a Moog, I'll just have to live with that :) If I could change the 490 interface, I would have only one input jack which would leave room for an input level knob. Imho, passive mixers aren't very useful unless you have a VCA for each input. I haven't decided if I want to try lowering resistors to increase the input level. While I'm on the subject of swapping resistors. Does anyone know a good way to unsolder MOTM PCB's?? They seem to delaminate very easily. Just removing R39 removed the foil around both pads. You don't even want to know about the 700 (I had to use silver to get the last repair to stick) I've tried using a Paladin solder sucker (spring-loaded vacuum) and a braid (Chemwick). Any ideas??
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490 resonance
2003-04-27 by media.nai@rcn.com
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