Tips for VCF tuning?

I currently trying to build an Ambika with SVF voicecards, and I have a question.

At the step of VCF tuning I tune as better as possible one voicecard as described in instruction page,
and for others voices I use the mono mode by pair with the first tuned voice and try to change
tuning by slowing the beat produced by the frequency difference of the two self-oscillations

Is it a good way to follow??

(sorry for poor english)

Yes, good approach! Don’t overdo it, though, it will vary a bit with temperature anyway.

When tuning the filter never know if i’ve to go up or down. Here on the forum i read the frequencies for octaves but can’t find or remember it…

Not sure I even tuned any of mine and it sounds fine :slight_smile:

Just curious, I remember like 1Mhz at C3 or something, that’s because this time i used the spectrum analyzer from Ableton, other times just use a stompbox tuner.

Huh? Your ears don’t go above 20k. 14 or 15k if you’re older, less if you’ve ever had more serious problems…

didn’t I say 1Khz? sorry…

Depending on which note numbering standard you use, C3 = 261.62 Hz or 130.81 Hz

was about to ask the same question here… i got almost all filters right on my ambika, but some are more off of a clear octave than others, not much but still quite impossible to get all the filters to the same value. i get self oscillation (filter and reso on 63 with no env or velocity modulation) 770 hz at C3 and approximately the double on C4. am i way too high with my self oscillation, or is it all ok?

Actually, tuning the filters in an ambika (at least on MI’s voicecards) is not going to have them all self-oscillate at the same note height. The tuning is only here to ensure (kind of) that playing 2 notes one octave apart is going to produce self-oscillation one octave apart. It’s not about the height of the notes but about the scale.
When i tune an ambika, I just use tubeohm’s fantastic tool (see here and click on “filter calib”) and tune one voicecard after the other. It’s pretty straightforward.
Having the voicecards not self-oscillating at the same exact height is in my opinion a good thing, it recalls the ‘analog’ nature of the synth.

yeah i use a guitar tuning vst myself. works like a charm (GTune VST).
and nothing wrong with a bit of “analog nature” ;). just wanted to know if i’m way up in scale

Well i got all my voicecards around 530 Hz at C3, and one of them want to go low so I suppose it’s good that all voicecards stay in the same range?

Again, in my opinion what really matters with the ambika voicecards is relative tuning (v/oct tracking) rather than absolute tuning. Olivier would have used 2 trimmers, one for v/oct scaling and one for the height if he thought that absolute tuning was really important. The only trimmer here is for v/oct adjustment.
I personally wouldn’t bother with voicecards not entering in self oscillation at the same height.
If you manage to do that for a certain note, it probably means that you’re going to be pretty out of tune 2 octaves above or below. Which is more annoying than 2 filters self oscillating 1/3rd apart on 3 or 4 octaves.

Ok, thanks. Let’s play!

Is it possible, that no tuning at all is necessary?
I build two SMR4 cards and both had correct tuning instantly - I think. And I didn’t touch the trimmers.
Is that strange or unlikely?

Not at all, trimmers are set in the factory at their middle position, and the circuit is designed so that the theoretical ideal position of the trimmer is very close to the center.

Build a midnight edition…… i don’t know why theres a trimmer at all, touching it made everything worse :wink:

Nice, very good to know!