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Dod envelope filter 440, HELP!


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11/23/1999 3:42 AM
Terry
Dod envelope filter 440, HELP!
.......i've been trying to make this friggin thing for almost a year and i can never get it , the closest i get is a light controlled sound...the more the light the the higher the pitch...also i have gotten it to where when i play it will distort to an extent, neither pots do anything audible and the led doesn't light up...i am 99% sure ive got most of the circuit right and i know i've got the ic hooked up right...can someone please help? or even better yet (i know its asking alot but...) make a pcb for me?  
 
 
THANK YOU SO MUCH!
 
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11/24/1999 12:21 AM
John Greene

Where did you get your schematic? There was one on the web a while back that I seem to remember had an error in it. I think there was a connection dot missing. I've built it with the correction and it worked just fine.  
 
--johng
 
11/24/1999 5:19 AM
Terry

Hi, got the schem from the link off of Aron's page...i didn't know there was a problem w/ it, do you think you could tell me the correction? and any other information that might help me ?  
 
THANX!
 
11/24/1999 6:20 PM
John Greene

I corrected the schematic and will Email it to you. The circuit is basically a Wien Bridge oscillator that is operated below the gain level needed to oscillate (3?). If you increase the value of the 430K the Q of the circuit will get higher up to the point it oscillates. I put a Pot in series with a 390K so I could have an adjustable Q. That's not reflected in the schematic however.  
 
--johng
 
11/24/1999 10:54 PM
Terry

Hmmm...that's interested, actually i put a 470k resistor in place of that 430k , would that have anything to do with the problem? Also , to me it seems that the circuit on "top" of the schematic works ok, but not the bottom, i'm going to check for voltages right away, since there is no response in the pots, (could a blown IC cause this problem,mine have been fairly used)  
 
THANX !
 
11/24/1999 11:56 PM
John Greene

I guess if tolerances worked enough against you the 470K could cause a problem. I had to get mine above 510K before it would oscillate on its own. The schematic I sent you has an extra 'dot' in the top part of the schematic. Make sure your circuit has this connection in it.  
 
--johng
 
11/25/1999 12:13 AM
Terry

Well, i'll measure the 470k resistor and try a couple others and see if it works, in your last post you said you sent the schem, but i haven't received it yet...so i can't do much else..maybe some new ics might help..  
 
TERRY
 

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