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 Forum index » DIY Hardware and Software » YuSynth
YuSynth VCO Tracking Problem. 1v/2Oct
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Luka78



Joined: May 07, 2019
Posts: 5
Location: italy

PostPosted: Tue May 07, 2019 5:00 am    Post subject: YuSynth VCO Tracking Problem. 1v/2Oct Reply with quote  Mark this post and the followings unread

Hello everyone,
I'm having a problem that I can't find a solution to. I have no more ideas.
All waveforms work fine, but during tracking calibration I can't get 1v per octave.
Starting from 55 hz (a1.0v in my cv keyboard), a2 is about 220 hz.
every semitone becomes a tone and 1volt equals 2 octaves.
I reviewed all the components and the pcb without encountering problems.
As power supply I'm using a Frequency Central Psu coming out with + - 15v and gnd.
If you can address me on the path to follow to resolve the issue, I would be grateful.
thx Luka
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gabbagabi



Joined: Nov 29, 2008
Posts: 523
Location: will be back soon in Berlin by n8
Audio files: 23

PostPosted: Tue May 07, 2019 6:17 am    Post subject: Reply with quote  Mark this post and the followings unread

hi and welcome to the forum

you have 1V coming from your keyboard and the VCO is oscillating at 55Hz,
what is the Voltage coming from your keyboard when the VCO is oscillating at 220Hz?

do you have the GND of the keyboard and the PSU connected?
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Luka78



Joined: May 07, 2019
Posts: 5
Location: italy

PostPosted: Tue May 07, 2019 6:33 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi g.gabba and thank you for your answer.
at 0v on my keyboard,i tune the frequency pot at 55hz.then when i play 1v up(1 oct) the frequency goes at 220hz.
i checked the voltage of my keyboard and is ok(1v/oct).
i forgot to say that i am using an as394 and a tempco. instead of an opa i am using a tl072.
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gabbagabi



Joined: Nov 29, 2008
Posts: 523
Location: will be back soon in Berlin by n8
Audio files: 23

PostPosted: Tue May 07, 2019 7:48 am    Post subject: Reply with quote  Mark this post and the followings unread

hm, just fishing a bit around in the dark:

do you have the GND of the keyboard and the PSU connected?

did you measured the tempco resistance?
may it is 2k instead of 1k?

is it on all 3 inputs the same?
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Luka78



Joined: May 07, 2019
Posts: 5
Location: italy

PostPosted: Tue May 07, 2019 8:04 am    Post subject: Reply with quote  Mark this post and the followings unread

Excuse me for not being clear. It is my very first experience in a forum Embarassed

I just measured the tempco resistance and yes, it's 2k.
yep,the same in all the v/oct input.
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Luka78



Joined: May 07, 2019
Posts: 5
Location: italy

PostPosted: Tue May 07, 2019 8:07 am    Post subject: Reply with quote  Mark this post and the followings unread

ahhh and yes i have the gnd of the kb and gnd of the psu connected
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Luka78



Joined: May 07, 2019
Posts: 5
Location: italy

PostPosted: Tue May 07, 2019 8:48 am    Post subject: Reply with quote  Mark this post and the followings unread

thanks g.gabba for pointing out to me the value of tempco resistance.
I put a 2k2 resistor in parallel with the tempco and now it seems to work!
thank you!
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gabbagabi



Joined: Nov 29, 2008
Posts: 523
Location: will be back soon in Berlin by n8
Audio files: 23

PostPosted: Tue May 07, 2019 10:41 am    Post subject: Reply with quote  Mark this post and the followings unread

dont worry, you are welcome!

glad to hear that it seems to work, at least better than before.

The tempco is a temperature dependent resistor, it is there to keep the frequency of the VCO stable when the (room)temperature is changing.

If you put a non-temperature-dependent-resistor in parallel to the tempco you will not get the (full) stability effect.

i guess it would be better to use a second 2k tempco in parallel, or raise r11 to 44k (solder a second 22k in series),
but i cant say for sure what is better

good luck
gabbagabi
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