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 Forum index » DIY Hardware and Software » YuSynth
problem: vco tuning
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pablop



Joined: Aug 22, 2018
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Location: france

PostPosted: Wed Aug 22, 2018 8:51 am    Post subject: problem: vco tuning Reply with quote  Mark this post and the followings unread

Hello,
I recently made the yusynth vco with the AS394CN. Today i tried to trim my circuit. The waveshapes and volt/oct tracking are working very nicely.
My problem is for the tuning, when T1 is at max range, with the freq pot fully counter clockwise, i cannot go below 50Hz (need to reach 16,2Hz apparently).
I built a 12V version and my I picked some 200k trimmers for T1. Should I go for a higher trim value (like 300k, 220k doesn't seems to be enough) or is there a problem in the circuit like a wrong resistor value (R8 is 470k) ?

I can put some photos if needed.

Of course the CV input was disconnected during the measurement.

Thanks for reading. If anyone can help me.
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Blue Hell
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Joined: Apr 03, 2004
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PostPosted: Wed Aug 22, 2018 10:09 am    Post subject: Reply with quote  Mark this post and the followings unread

Without seeing a schematic I'll have to guess .. but could put a resistor (about the same value as the pot resistance) at one of the ends of the pot (positive side) .. or likely could change the value of the summing resistor (make it larger, maybe twice as large) coming from middle of the pot into the input summing opamp.
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pablop



Joined: Aug 22, 2018
Posts: 5
Location: france

PostPosted: Wed Aug 22, 2018 10:47 am    Post subject: Reply with quote  Mark this post and the followings unread

Thank you for your answer. Here is the schematic:

Posted Image, might have been reduced in size. Click Image to view fullscreen.

The trimmer T1 is next to the 5 inputs at the left.
So i should just put a resistor between +12v and the trimmer?
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Blue Hell
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Joined: Apr 03, 2004
Posts: 22567
Location: The Netherlands, Enschede
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PostPosted: Wed Aug 22, 2018 12:12 pm    Post subject: Reply with quote  Mark this post and the followings unread

Ow .. opps .. I posted my reply to the wrong thread Shocked

this was meant to be the answer for http://electro-music.com/forum/topic-70246.html - sorry.

Ok .. let me actually read the question then Confused

to make it go lower you could lower the value of resistor R8, that would give you more range trimming. When that does not work you could choose a higher value for the timing cap C8.

Oh and welcome to the forums.

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Marco Piatti



Joined: Aug 08, 2018
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PostPosted: Wed Aug 22, 2018 12:47 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi, Did you previously trim the 1V/Oct trimmer? That can also alter the minimum possible Frequency
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pablop



Joined: Aug 22, 2018
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Location: france

PostPosted: Wed Aug 22, 2018 1:14 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thank you very much for the answer. I just tried to change r8 by a 270k resistor.
The trimmer range is now good. Trimmering was quite sensitive maybe 270k is a bit low but that was the only value I had left.
But more importantly the vco is working perfectly fine now. A4 is 440.3hz, the V/oct works perfectly fine and the waveshapes are ok.

Thank you again.
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pablop



Joined: Aug 22, 2018
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PostPosted: Wed Aug 22, 2018 1:27 pm    Post subject: Reply with quote  Mark this post and the followings unread

For trimming i followed the steps on the yusynth site. So i trimmed in this order : waveshape-->V/oct-->tunning

I have a second vco to make, do you think i should trim the tunning right after the waveshapes?
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Hubaswift



Joined: Jul 06, 2016
Posts: 69
Location: Canada

PostPosted: Fri Aug 24, 2018 5:19 pm    Post subject: Reply with quote  Mark this post and the followings unread

At one point I had a similar problem and changing R15 to a lower value decreased the minimum frequency.
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pablop



Joined: Aug 22, 2018
Posts: 5
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PostPosted: Fri Aug 24, 2018 6:02 pm    Post subject: Reply with quote  Mark this post and the followings unread

I just did a second vco with the same components, had the same problem with tunning. Problem solved the same way. Must be my components values.
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