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 Forum index » DIY Hardware and Software
Why does this filter have two capacitors? And other queries.
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Werebear



Joined: Nov 23, 2009
Posts: 33
Location: UK

PostPosted: Tue Jun 04, 2013 1:51 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi

after following this thread here's my variations.

Voltage control is achieved with a BC 547 with a 100K resistor across it as in the pic synth filter. The mix resistor on the gate of the transistor started as 1M as in Jinglejoes sketch but fiddling around I found 10K gave a good sweep. The frequency pot will need a range resistor to ground but haven't tried it out yet, but the range on the pot is nearly the full turn.

Looking at Tim Escobedos Q+D VCF, the second variant has caps of different values and remembering what Joe said about the position of the caps having an effect on resonance I played around with values until I got something that sounded good to my ears. In an attempt to have some play in the range of the resonance pot I used a 1K pot in the hope that the range wouldn't be squashed into the last few degrees of turn. It kinda isn't but would like to use a smaller value pot still. I also experimented with using a separate cap with a pot, 470 pF and a 10K, but that didn't work so well.

I've played with this type of filter before without much success but after reading this thread and with the Jingle man's sketch I bread boarded it up and it worked first time! Playing with it was a process of swapping out components until I got something pleasing to my ear and a satisfying twiddle factor.

Thanks to everyone who took time to demystify twin T VCFs.


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