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 Forum index » DIY Hardware and Software » MusicFromOuterSpace.com designs by Ray Wilson
filter help needed...
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cassandra87md



Joined: Dec 20, 2013
Posts: 1
Location: takoma park, md

PostPosted: Fri Dec 20, 2013 9:55 pm    Post subject: filter help needed... Reply with quote  Mark this post and the followings unread

Hi,
I'm working on a drone synthesizer. I've finished the oscillators (six simple two op amp square/tri oscillators) and a simple active mixer. That all works fine, and is soldered onto a protoboard. I'm trying to feed the output to the simple VCF from the noise toaster, currently built on a breadboard. I'm not using the voltage control portion of the filter (the inputs from the LFO and ARG), just the frequency and resonance pots, the two .001uF caps, and the 4M feedback resistor.
It's not working. I've built it about 12 times, so I don't think I have any clear wiring issues... The behavior is odd. With no input whatsoever, the output is a square wave. What I have noticed is that this behavior appears as soon as I connect the non-inverting input to the virtual ground. I had a separate virtual ground on my breadboard, and I noticed that if I tied into the virtual ground on the protoboard, it fed back into the mixer and the output of the mixer was the input from one of my oscillators plus the oscillation of the filter.
Does this sound familiar to anyone? I do not have a lot of experience building electronics, so problems that are probably obvious to others have taken me a lot of time to troubleshoot, but I've come this far, there's no going back now.
I've modified things from my original schematics, but I can draw up a new one tomorrow if that's helpful.

Thanks!
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alieneYe



Joined: Jul 25, 2008
Posts: 34
Location: Phoenix, Az

PostPosted: Sat Dec 21, 2013 2:03 pm    Post subject: Reply with quote  Mark this post and the followings unread

i had this problem when bread boarding part of the noise toaster. what op amp are you using for this? i tried to do it with a tl072 but it would not work until i replaced it with an LM358. when i did that it worked out good. it is just the dual version of the LM324. i think it is an input independence issue

good luck
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 Forum index » DIY Hardware and Software » MusicFromOuterSpace.com designs by Ray Wilson
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