Hey all, I have a question for a project I have that I am not certain about. I’ve made a version of LMNC’s performance VCO that I have posted about the trouble I have calibrating it on here in the past and has worked for the most part since. The main issue being while the VCOs are calibrated in the middle position of the rotary switch and a midi controller, the moment I switch the position, instead of going up or down an octave, it does to another note and is not calibrated. In the original schematic, it requires 10k resistors with a tolerance of ±0.1%, which is fine and dandy as through-hole resistors, but since it is SMD (1206), I am having trouble finding them. I bought some from ebay with the supposed specifications which I received today and used them on of the VCOs, and it pretty much did nothing. I did verify this they are 10k, but have no way of testing the tolerance or know of a method that can. Can anyone provide some advice on finding the right resistors and a way to verify they are in fact ±0.1%?
I would suggest a more reputable dealer. Mouser has a handful of them. Such as,
The only way to test the resistors is with a meter of appropriate precision and accuracy.
Have you verified the internal tuner against an external tuner or is the change in pitch readily apparent?
Have you verified that your MIDI to CV is putting out 1V/Oct?
1% resistors in the octave switch might give you out-of-tune octaves, but “instead of going up or down an octave, it does to another note” sounds like a much worse problem than that, one that precision resistors won’t fix — unless the original resistors are off by a good deal more than 1%. If the reference voltage isn’t dead on 4.00 V for instance that could explain it.
On the other hand, getting it into accurate tune will require resistors matched at the 0.1% level. Not necessarily 0.1% tolerance, they could all be 1% off as long as they’re all off the same amount. At $0.55 each for precision resistors, hand matching may be cheaper, but then again you only need four of them.
Yeah it’s weird with the octave issue because when I calibrate the vco without a 1/v source (say like my midi to cv converter), it’s able to go up the octaves just fine with no issue. The moment I plug in a 1/v source, it is no longer calibrated and when I re-calibrate it, I get that issue. I’m going to check the reference voltage which should be 4.00V since last time, but then I kind of remember that the original SMD resistors I used were I think 1%, and since the “precision” “0.1”% resistors I got basically gave me the same results, in fact I think they gave me the same notes on the octaves as last time, I think they might be just your typical 1%