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 Forum index » DIY Hardware and Software » fonik's place
VCO won't track properly..
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LektroiD



Joined: Aug 23, 2008
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PostPosted: Fri Sep 16, 2011 9:55 am    Post subject: VCO won't track properly.. Reply with quote  Mark this post and the followings unread

I'm just building my second VCO (I'm delighted with the first, it works brilliant).

I have an issue with the tracking though, even on the widest scale setting, it is not wide enough to give a full octave.

Readings as follows (trimmed to widest scale setting):
1V = 100Hz (base frequency)
2V = 194Hz (should be 200Hz)
3V = 386Hz (should be 400Hz)
4V = 772Hz (should be 800Hz)
5V = 1554Hz (should be 1600Hz)

I was wondering if changing R1 for a higher value (1K or something) would rectify the problem. I'm running it on 12V.
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fonik



Joined: Jun 07, 2006
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Location: Germany
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PostPosted: Fri Sep 16, 2011 1:05 pm    Post subject: Re: VCO won't track properly.. Reply with quote  Mark this post and the followings unread

LektroiD wrote:
I'm just building my second VCO (I'm delighted with the first, it works brilliant).

I have an issue with the tracking though, even on the widest scale setting, it is not wide enough to give a full octave.

Readings as follows (trimmed to widest scale setting):
1V = 100Hz (base frequency)
2V = 194Hz (should be 200Hz)
3V = 386Hz (should be 400Hz)
4V = 772Hz (should be 800Hz)
5V = 1554Hz (should be 1600Hz)

I was wondering if changing R1 for a higher value (1K or something) would rectify the problem. I'm running it on 12V.


so it's coming a little short?

1st: running on 12V does notmake any difference.
2nd: which 4046 are you using?
3rd: R2 should be 390R NOT 100k as seen on the old BOM.
4th: you may want try to jumper R2 completely
5th: changing R1 shouldn't make any difference then (see 4th), since it is set up as a voltage divider.

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bubzy



Joined: Oct 27, 2010
Posts: 535
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PostPosted: Sun Sep 18, 2011 1:12 pm    Post subject: Reply with quote  Mark this post and the followings unread

im also getting range problems with mine, i have tried several ic's including mc14046, a national 4046, and the XNP HEF4046BP im getting a maximum of 3.8k hz (roughly) with a very slight variation between chips.
ive tried jumpering R2, doesnt seem to do much for the overall range




**edit** AHEM......i seem to have used a 100nf cap in C3....... Very Happy sorry. and ty JovianPyx for pointing me in the right direction.
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LektroiD



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PostPosted: Thu Sep 22, 2011 5:29 pm    Post subject: Reply with quote  Mark this post and the followings unread

My problem appears to have stemmed from absent mindedness; I didn't allow warm up time.. Left it switched on overnight, and now it tracks perfectly. I now have all 4 built and they sound magnificent!
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fonik



Joined: Jun 07, 2006
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PostPosted: Fri Sep 23, 2011 1:37 am    Post subject: Reply with quote  Mark this post and the followings unread

LektroiD wrote:
I now have all 4 built and they sound magnificent!

that's what we wanted to hear!

LektroiD wrote:
I didn't allow warm up time.. Left it switched on overnight, and now it tracks perfectly.

Shocked
you mean, you needed to run the modules several hours until they tracked properly? then there is still something wrong, i believe. the scale should be fine right after powering-up the module...

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matthias
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JingleJoe



Joined: Nov 10, 2011
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PostPosted: Sun Nov 13, 2011 7:55 am    Post subject: Reply with quote  Mark this post and the followings unread

fonik wrote:

LektroiD wrote:
I didn't allow warm up time.. Left it switched on overnight, and now it tracks perfectly.

Shocked
you mean, you needed to run the modules several hours until they tracked properly? then there is still something wrong, i believe. the scale should be fine right after powering-up the module...

But a huge warm up time is significantly more retro and therefore cooler Cool
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fonik



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PostPosted: Sun Nov 13, 2011 8:46 am    Post subject: Reply with quote  Mark this post and the followings unread

Laughing
valid point!

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widdly



Joined: Jun 25, 2007
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PostPosted: Wed Nov 14, 2012 11:22 pm    Post subject: Reply with quote  Mark this post and the followings unread

Sorry to dig up an old thread but I am having the exact same issue. I built my x4046 over the weekend and I could only get 11 semitones per volt tracking. I tried a TI and a national 4046 and got the same results. I used 1% resistors through out.

After lowering the 100k resitor to about 90k on the 1v/oct input I was able to get 1v/oct very easily over at least 5 octaves. Nice!

The other thing I found was I was able to trim the VCO offset without an oscilloscope by using a Multimeter set to DC voltage reading.
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fonik



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PostPosted: Thu Nov 15, 2012 2:25 am    Post subject: Reply with quote  Mark this post and the followings unread

the TI part is known to not meet the criteria. the national, however, has been used in the past with success. you are the 1st one to have problems with the national. alas, i used the NXP part only, so i cannot say anything about the national...

anyways, glad you solved it. five octaves is not the best result, nevertheless, it makes this VCO usable for almost all musical applications, i believe.

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matthias
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