AS3340 tuning (was Super exciting Alfa3340 question!)

DIY STUFF
1

Hello. I built thogre’s 3340 oscillator (alfa4vco) and while it makes beautiful sounds, I cannot get it calibrated. As soon as I get close to getting the octaves in tune I run out of turns on the 10k trim pot.

I am using a keystep pro to tune.

My (potentially flawed) tuning procedure:
turn freq knob to 100hz
play octave above on keystep and tune the trim pot till I reach 200hz
go back down an octave and turn the freq pot
back and forth, etc

I used a 750 ohm resistor that goes from -12v to pin 3 of 3340 instead of 620 because I failed to understand that I wouldn’t get -7.4 volts without the chip being installed.
I also didn’t have a 1.8k resistor, so I used a 1.5k resistor for R11, but I don’t think that would affect tuning.

Before I start pretending like I know what I’m doing, would anyone care to give me some pointers?

Thanks

3340VCO_THOGRE
3340VCO_THOGRE3425×2478 279 KB

2

That isn’t the way to do the tuning. See this:

3

Thank you! That is by far the best explanation I have read. I still couldn’t get it in tune across multiple octaves as I hit the end of the trim pot. I changed some resistor values to exact specs and will report back. I noticed that the trim pot I am using only goes to 8.99 k rather than 10k at its full clockwise rotation.

4

I replaced the chip and got it in tune within 5 minutes.

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