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Re: Dod envelope filter 440, HELP!

11/25/1999 2:50 AM
John Greene
Re: Dod envelope filter 440, HELP!
I emailed it to the address you have on your posts and it didn't bounce.... Oh well, you can see it here:  
And now, a word from our sponsors:

11/25/1999 7:08 AM

I guess my email was gone for a while...sorry. I saw the schematic correction and put it in , i actually had it in already but still there is nothing...i don't know what could be wrong!  
The IC is hooked up right.  
The LED/Photocells are hooked up right  
And i am pretty sure the rest of the circuit is good.  
What could be wrong?  
Bad ic? Drifting values in worn resistors? Bad caps?  
The signal is getting through, usually clean, cover the photocells a little and it starts making some weird overdriven *filter-like* sounds , so i feel i am pretty close  
The LED doesn't light up  
The Pots don't work  
There is some voltage coming to the lower part of the circuit  
PLEASE HELP.......  
11/25/1999 7:04 PM
John Greene

Ahhh! I just remembered there is another error! The LED is shown in the wrong direction!
11/25/1999 7:08 PM

REALLY? Would the diodes be shown in the wrong direction too?  
I will try this, hopefully it works.  
11/25/1999 7:44 PM

I tried reversing the LED, and also tried changing the LED and reversing that one too but still it doesn't light up..  
Correct me if im wrong but istn't the LED light up according to how hard you nail the strings, and the harder the hit the more the filter?  
I'm sorry to drag this on like this, but i am desperate.  
11/25/1999 9:23 PM
John Greene

You have it right. The LED should get brighter the louder you play. The two diodes on the opamp are in the correct orientation. Check the voltages on all the pins of the opamp. They should all be around 4.5 v except for pins 8 & 4.  
11/26/1999 5:08 AM

I measured the voltages on the pins of the opamp, they came out like this:  
Pin 1: 4.5  
Pin 2: 2  
Pin 3: 4.5  
Pin 4: 0  
Pin 5: around 2.5  
Pin 6: around 2  
Pin 7: 4.5  
Pin 8: 9  
These figures seem a little wierd, do you think it could be a blown opamp? IF it is blown, do you think it could cause it to not work properly like it is now?  

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