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 Forum index » DIY Hardware and Software » YuSynth
VCO troubleshooting: sine converter top issue and drift
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intoodeep



Joined: Mar 14, 2010
Posts: 7
Location: los angeles

PostPosted: Fri May 21, 2010 1:11 pm    Post subject: VCO troubleshooting: sine converter top issue and drift Reply with quote  Mark this post and the followings unread

Hi! Thanks as always for your wonderful designs and support Yves (and everyone else). I've got (among several other yusynth modules sitting on my desk) a couple VCO's I'm trying to debug. There are two issues I would love your feedback on, both generally exhibit them although one is worse than the other.

First of all, the stability is very bad. I am using a tempco and two BC547b's and haven't gotten it all thermal pasted to the transistors yet. However, the tempco has some paste on it already and is touching the transistors, yet, i can blow on them and it changes the frequency so much that at 0V input I have to adjust the coarse frequency pot to get a signal again. Is this typical? Could my matching of the transistors be at fault or is it likely an insufficient thermocoupling issue?

The tracking is also waaay off, I am getting 0V - 55hz, 1V - 330hz, 2v - 750hz, not sure what could be causing this, maybe mismatched transistors in the expoconverter?

Second, the bit of the tri-sin converter that does the tops of the waves seems to not work except at fairly high frequencies. Under 12Khz or so, the tops of the sin wave are triangles. Part of me wants to leave this and see if it sounds cool, but part of me also wants to at least know what could be wrong. One of the matched pair of diodes is dead or mismatched or something maybe? I changed R23 from 100K to 82K, no difference.
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Sebo



Joined: Apr 27, 2007
Posts: 560
Location: Argentina

PostPosted: Sat May 22, 2010 8:34 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi:
It seems to me that the tracking problem, and the sine shape problem are caused by lack of calibration.

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