søndag 29. desember 2013

Oh well - some errors are to be expected

While trying to tune the oscillators I discovered two errors. They are both easily fixable but important. First, I had used 100k instead of 10k pots for the wave balance pots, which means it was impossible to get a good balance around 0V. I replaced the pots and it worked very well.

Second, both this quad oscillator and my stock yusynth oscillator seemed to have a very high-pitched response to 0V CV. Only after reading through the text on the yusynth.net site did I realize that the coarse tune pot is not centered around 0. Instead, the maximum counter clockwise setting is 0 and the max clockwise setting is 10 (not sure if that means 10 octaves though). This means that in order to function "normally", I have to add a 270k resistor connected to -15V to my design as I have no coarse tune pot. It's not a big problem but one that will have to be adressed in a version 2 of the oscillator. I should also concider adding either an octave rotary switch or at the very least an octave/coarse tune input. As I have run out of space on the PCB, I think the pot will have to affect all oscillators, not only one, meaning all four oscillators will be tuned to the same range. Two four-oscillator cards could of course be tuned differently though. I may even be able to squeeze in two inputs so that groups of two oscillators may be tuned differently.

One final note: I have used 100k resistors for the wave amplitude amplifier input. Mr. Usson states that one may have to use an 82k resistor here and I can see why. My saw wave output has a +/-4V amplitude instead of the expected 5V, swapping the resistor may help.

UPDATE: Fixed!
Four 270k resistors soldered directly to the back of the board, with a common wire to -15V. The molten plastic gunk is clearly visible too. What a shame.

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