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 Forum index » DIY Hardware and Software » YuSynth
Yusynth 4072 VCF self oscillation frequency range
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minisystem



Joined: Nov 16, 2012
Posts: 35
Location: Toronto

PostPosted: Thu Oct 24, 2013 8:10 pm    Post subject: Yusynth 4072 VCF self oscillation frequency range Reply with quote  Mark this post and the followings unread

I've built a couple of SMT versions of the 4072 VCF. It uses BCM857 matched pairs and SMT versions of everything else in Yves' design. R43 is omitted so there is no high Q compensation. My question is about self-oscillation at maximum resonance. After adjusting T1 to eliminate 40 Hz bleedthrough when cutoff is at its minimum (as per calibration procedure), I can get a near perfect 20-20KHz frequency response when self-oscillating on one of the builds, but on a second identical build I can only get about 100 Hz to 5-6 KHz self-oscillating sine wave. This difference really impacts the sound and character of the filter. Adjusting T1 can increase the upper range of the frequency response, but results in bleedthrough at lower frequencies. Any suggestions for component value changes or replacements?
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yusynth



Joined: Nov 24, 2005
Posts: 1229
Location: France

PostPosted: Sat Oct 26, 2013 11:57 am    Post subject: Reply with quote  Mark this post and the followings unread

Check the transistor pairs one or two may not be perfectly matched. Check also the LM3900 it may be faulty.
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