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 Forum index » DIY Hardware and Software » YuSynth
IMPROVING MOOG VCF RESONANCE
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muna93



Joined: Feb 24, 2013
Posts: 2
Location: Italy

PostPosted: Sun Feb 24, 2013 12:55 pm    Post subject: IMPROVING MOOG VCF RESONANCE Reply with quote  Mark this post and the followings unread

One year ago I built a full yusynth modular.
Now I'm building another one...
I've got an issue with the transistor ladder filter: resonance starts at something like 100Hz and goes through all the udible range. May I change some resistor values around the output stage of the filter (the two differential pairs on the right of the schematic) to increase the gain of the inverted feedback signal?
And also, what's the formula to compute the gain of the transistor output stage?
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yusynth



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

PostPosted: Tue Feb 26, 2013 5:10 am    Post subject: Reply with quote  Mark this post and the followings unread

As a matter of fact the Minimoog filter does not auto-oscilate under 100Hz, this is how it was designed. However if you wish to change that you can first change the values of C9 and C10 (for example put 680nF instead of 220nF , or even bigger). Then if you increase the gain of the transistor AOP you will get right into saturation because it's already at maximum gain. Anyway you may reduce the values of R24 and R27.
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muna93



Joined: Feb 24, 2013
Posts: 2
Location: Italy

PostPosted: Tue Feb 26, 2013 5:42 am    Post subject: Reply with quote  Mark this post and the followings unread

Wow! sounds cool... I will try out changing caps!
For the gain of the transistor AOP I really like the right amount of saturation that comes into the filter with regular resistor values so I wouldn't change them Very Happy
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isak



Joined: Dec 13, 2009
Posts: 625
Location: Israel
Audio files: 18

PostPosted: Tue Feb 26, 2013 7:49 am    Post subject: Reply with quote  Mark this post and the followings unread

Hello.

Just want to make it clear for my self...
the yusynth minimoog vcf design don't self oscillate from 20Hz to 20kHz like his arp vcf design?
It's starts from 100Hz?

Cheers.

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yusynth



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

PostPosted: Tue Feb 26, 2013 8:36 am    Post subject: Reply with quote  Mark this post and the followings unread

Yes correct just like the original minimoog filter.
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isak



Joined: Dec 13, 2009
Posts: 625
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PostPosted: Tue Feb 26, 2013 9:06 am    Post subject: Reply with quote  Mark this post and the followings unread

I didn't knew that!
I'm so happy you did that and keep the authentic of the filter, well done!

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