Accurate tuning range

[veracohr]

Hello everyone. I've recently finished building my x0x, and while I haven't had any problems with it I do have one question regarding oscillator tuning.

Is it normal for the range of accurate tuning (within an acceptable margin of error) to be barely one octave? If I tune it so that, say, the low C key (1) is as in tune as I can get it (via front panel tune knob), the upper C key (8) is too out of tune. I can tune it to a (more or less) happy medium where both ends are acceptably out of tune, and in tune is somewhere in the middle, but then of course any notes outside that 1-octave range are even more out of tune.

This can be acceptable for some patterns and tracks, but maybe not others. Is it normal to have barely/not even a one octave range of accurate tuning?

Thanks.

[decoder23]

you should tune the x0x with the trimmers tm4 and tm5 and not with the tune pot. here in the forums you can search for a nice plugin from antto which makes tuning pretty easy

Edit: here is the link http://forums.adafruit.com/viewtopic.php?f=12&t=24759

[veracohr]

I tuned with TM4 and TM5 after I finished soldering the VCO, as described in the build manual. Perhaps I should have another go at it? Maybe I didn't do it accurately enough.

So I should expect more than an octave of accurate tuning range?

[antto]

the manual probably suggests tuning by tweaking TM4 and TM5 iteratively
IMO this is the wrong way (not that it's not possible, it's just boringly slow)
the tutorial i made suggest tuning by tweaking TM5 first, then TM4 (just two steps)
and yes, when TM5 is set correctly (the octave width) then all octaves should be nice

something else i figured.. if the lower notes become out of tune (they might collapse towards some frequency)
this is due to the opamp responsible for amplifying the pitch CV - IC11 which is marked as a rare part in the BOM (AN6562 or something)
and i strongly suggest socketing this
in my x0xb0x (which has been built by x0xsource) i got this part in IC11 and it worked fine
but then, i wanted to extend my firmware to use 60 notes (unlike the other firmwares) and i figured the lowest notes got squashed, even tho the upper are perfectly in tune
i desoldered IC11, soldered a socket, tryied a bunch of other LM358-compatible dual opamps, and it was TS272CN which did the job

and last, if from octave to octave everything is in tune, but the notes in the middle of each octave are bad - this gotta be the resistor network, which is responsible for dividing the pitch into equal semitones or something
if that's the case, you really need low tolerance resistors there, and better measure them with a multimeter (those 1% should work)

[veracohr]

I'll try retuning again. Now that I think about it, I remember saying "good enough, I'll fine-tune it when it's all done". But I think I forgot to do so.

I think my resistor network is fine. I don't mind some small bit of variance, I just want a wider range.

Thanks!