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 Forum index » DIY Hardware and Software » Developers' Corner
Help with Q&D VCF
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hway23



Joined: Jul 23, 2008
Posts: 61
Location: ks

PostPosted: Thu Jan 22, 2009 4:47 pm    Post subject: Help with Q&D VCF Reply with quote  Mark this post and the followings unread

Hello, I am having a small bit of trouble with the Q&D VCF http://www.geocities.com/tpe123/folkurban/fuzz/simplevcf.gif
I am having some problems understanding the schematic, and here are my questions:

1. What does Vr stand for? virtual ground right?

2. Shouldn't Vr be going into the inverting input?

3. Why isn't v- connected to anything?

4. Am I supposed to use that teeny schematic in the corner? or is that optional?

5. Will the lm741 do the job?

Thanks!
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richardc64



Joined: Jun 01, 2006
Posts: 679
Location: NYC
Audio files: 26

PostPosted: Sat Jan 24, 2009 1:28 pm    Post subject: Re: Help with Q&D VCF Reply with quote  Mark this post and the followings unread

hway23 wrote:
1. What does Vr stand for? virtual ground right?


Well, it's more like a pseudo ground

Quote:
2. Shouldn't Vr be going into the inverting input?


The schematic shows it going to the non-inverting input through a 1M resistor and I assume that's correct. This is very simialr to the filter in the WSG.

Quote:
3. Why isn't v- connected to anything?


If by v- you mean the negative end of the battery or -9v, that goes to the circuit's real ground, every point with a Gnd symbol.

Quote:
4. Am I supposed to use that teeny schematic in the corner? or is that optional?


That's an alternative way to connect the l.e.d. so that a higher control voltage causes a lower cutoff frequency.

Quote:
5. Will the lm741 do the job?


It should.

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