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 Forum index » DIY Hardware and Software » YuSynth
VCO CV calibration
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Conboy



Joined: May 01, 2009
Posts: 25
Location: London

PostPosted: Fri May 01, 2009 1:36 am    Post subject: VCO CV calibration
Subject description: VCO CV calibration
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I had been annoying Yves on his private email with my questions but have just discovered this place. Great!

Just finished building my first VCO and incredibly it works first time and beautifully. Managed to do all the tweaks fine but have an issue with the CV calibration.

Start on A1 55Hz get A2 to read 110Hz... fine.
however on the next and subsequent steps, A3 starts at 250Hz so when adjusted to 220Hz A2 has gone out again to approx 103Hz. This gets progressively worse through the octaves.

How does one get around this intonation problem?
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Sebo



Joined: Apr 27, 2007
Posts: 539
Location: Argentina

PostPosted: Fri May 01, 2009 7:55 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi:
Tunning the VCO is a little tricky. In my first attempt it happened the same as you.
The key is to understand what Yves wrote at his site (I didn't the first time).
For example you tune A0=55Hz then jump an ocatve higher, if A1 is lower than 110Hz you have to lower (yes lower) the tunning using the V/Oct trimmer.
If A1 is higher than 110Hz you have to rise (yes rise) the tunning using the V/Oct trimmer.
How much? just try.
Then go again to A0 and retune usiing the tunning trimmer (or fine tune).
Repeat until you get the first octave working, then go to the second octave and do
the same.
Note that the use of the V/Oct trimmer is opposite to what one think is right.
Hope this Help.

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Last edited by Sebo on Fri May 01, 2009 8:03 am; edited 1 time in total
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numbertalk



Joined: May 05, 2008
Posts: 980
Location: Austin, TX
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PostPosted: Fri May 01, 2009 8:01 am    Post subject: Reply with quote  Mark this post and the followings unread

I had a similar issue with the Oakley VCO recently and found the exact same thing is ultimately what worked - it's counterintuitive but seems to be the way to do it.
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Conboy



Joined: May 01, 2009
Posts: 25
Location: London

PostPosted: Fri May 01, 2009 10:33 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks. I get the concept of having to go in the opposite direction what one might think. That's not the problem.
The difficulty is that once I start tuning the second or third octave etc the octaves below (that I tuned previously) go out.

So I could say get A1 correct at 55Hz and A6 bang on at 1760Hz. Great, but all the octaves in between will then be out...? The intonation is wrong.
I don't really understand why the procedure is to do one octave at a time. What difference will it make from just tuning A1 and say A5 or A6 to be correct?


I don't see a way around this without changing some component values... and I don't know which ones!!!?

What is the option to change R23 to 82k all about BTW?

Still.. besides this little problem I can't get over how wonderfull this baby actually sounds!
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Conboy



Joined: May 01, 2009
Posts: 25
Location: London

PostPosted: Sun May 03, 2009 3:38 pm    Post subject: Reply with quote  Mark this post and the followings unread

After a few days of mulling it over I realised that everything could be so much simpler.
So I decided to employ the best best test equipment known to man.

MY EARS!!!

Playing up the octaves on the keyboard and twiddling the V/Octave trimmer till it sounded right, the bugger was calibrated in about 2 minutes. Checked against a test oscillator (Logic) and then on the old freq counter, with a little nudge all is now perfect!

Just like calibrating me old VCS3. Mere perseverance.

Sweet
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yusynth



Joined: Nov 24, 2005
Posts: 1224
Location: France

PostPosted: Sun May 03, 2009 11:03 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi

I am a bit late regarding this thread, but yes I found it also easier to use a cheap Korg CA chromatic tuner than a precise frequency counter, it is so because the frequency counter is a bit too accurate while the tuner does some acceptable rounding.

Because of the circuit design the way the V/oct trimmer has to be adjusted seems quite counter intuitive, this mainly because the v/oct is the last element in the tuning chain and the tuning pots pass through it and therefore are influenced by it. I also found that it might be faster to go the other way round, starting with a high note instead, tuning C5 for example and then pressing C4, adjusting the V/oct trimmer, going back to C5 retune, then going to C4, and so on.

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