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 Forum index » DIY Hardware and Software » YuSynth
MiniMoog VCF Clone CV Feedthrough
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moogasm



Joined: Dec 29, 2009
Posts: 13
Location: San Diego

PostPosted: Tue Dec 29, 2009 9:28 pm    Post subject: MiniMoog VCF Clone CV Feedthrough Reply with quote  Mark this post and the followings unread

Hello this is my first post. I retrofited my Crumar Spirit with the Yusynth Minimoog VCF and I really like it alot. It is running off of +-12V and I am using LM394 and CA3146 ICs. It self-resonates though the v/oct scaling is not perfect. One thing I have noticed is the filter exhibits some control voltage feedthrough in the form of a low frequency pop with short duration CVs and get louder as the CV is increased even with no signal present. I am curious to know why this happens and of course how to eliminate or reduce it. My Minimoog has almost no CV feedthrough. Any insight would be much appreciated.
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yusynth



Joined: Nov 24, 2005
Posts: 1214
Location: France

PostPosted: Wed Dec 30, 2009 4:18 pm    Post subject: Reply with quote  Mark this post and the followings unread

There may be for two reasons, the transistors of the ladder are not matched thoroughly or (and this happened to me when I designed the prototype) the CA3046 that drives the ladder is bad and must be replaced by a good one.
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Yves
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moogasm



Joined: Dec 29, 2009
Posts: 13
Location: San Diego

PostPosted: Sun Jan 03, 2010 8:42 pm    Post subject: Reply with quote  Mark this post and the followings unread

Yves, I figured out my problem was due to excessive gain in the output opamp stage. The input level was too low so I compensated by increasing the output gain. Any CV feedthrough also got amplified. Once I corrected the input level and reduced the output gain the CV feedthrough problem was solved.

Thank you for sharing your great designs and expertise with the synth community.

Best regards,
Mike
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yusynth



Joined: Nov 24, 2005
Posts: 1214
Location: France

PostPosted: Mon Jan 04, 2010 12:34 am    Post subject: Reply with quote  Mark this post and the followings unread

tihsmud wrote:
Yves, I figured out my problem was due to excessive gain in the output opamp stage. The input level was too low so I compensated by increasing the output gain. Any CV feedthrough also got amplified. Once I corrected the input level and reduced the output gain the CV feedthrough problem was solved.

Thank you for sharing your great designs and expertise with the synth community.

Best regards,
Mike


OK then enjoy your filter Wink

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Yves
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