nurse quacky debug

Started by Andy73, June 17, 2008, 05:20:50 PM

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Andy73

I am still very much in the learning stages here so please bear with me if I sound stupid....  My wife already gives me that comment enough!  ;)

I decided to design a vero layout and build so I could better understand the circuit. (and circuits in general)

This is the schematic I used  http://www.home-wrecker.com/nurse-quacky.html

This is the vero layout I made.  I had 1 mistake that I found at R8, that is why it is just run to a wire now.  There is a very good possibility that I may have this all screwed up.  If that is the case I don't expect you to solve the whole thing for me, just let me know I need to start over....  And maybe give me a couple of hints ;)
http://i251.photobucket.com/albums/gg312/lumsden73/envelopefilter.gif

The only substitution I made was a 20K pot on the attack instead of a 25K.  I am using 2- 3mm yellow led's.

I am getting no sound with the effect engaged.  Bypassed the signal goes through.  I tried all ranges on the pots.  With an input signal I get one led on solid and the other blinks according to the input signal.

Voltages with power supply and no input signal - with LM358 - (pins 1,2,3 refer to the bottom half on the schematic.)
1.  1.4
2.  .4
3.  1.5
4.  0
5.  4
6.  4.4
7.  4.4
8.  8.8

Transistor is 2N3904 and reads 0 on all three legs.

With an audio probe hooked to my input I get the signal to the amp when I touch the output point on the board.  If I move in front of the output cap(.1uf, C4 on my layout) I get no signal.  If I remove the front leg of the cap (nearest transistor) from the board and then test to it, I get a signal.  So, I assume there is something wrong on that strip connected to pin 7 of the IC?

With an audio probe connected to my output I get a signal to the amp when I touch in 'In' on the vero board.  When I touch the second leg of the .01 cap (C1 in my layout, the sode closer to the IC)  I get no signal.

I have replaced the IC, tried a TL072 which gave me similar readings and the same results, replaced the transistor, put the transistor in the other direction.

Thanks to anyone who can give any help and/or provide me with a next level of troubleshooting!

-Andy

petemoore

1.  1.4  Very low, not biased
2.  .4    ....
3.  1.5    ....
4.  0 
5.  4      Not bad...
6.  4.4   1/2v
7.  4.4   1/2 of supply
8.  8.8   good

Transistor is 2N3904 and reads 0 on all three legs.
This is where I'm of limited resource to help.
It looks like it's not connected to the power supply...of course the schematic looks like that too...the collector all DC blocked 'n stuff, no V+ type bias, only the 47k to ground on the collector...youch...this is where my understanding takes a leap off of the 'ol learning curve. 
Convention creates following, following creates convention.

mdh

To add to Pete's comments, one thing I noticed is that you have the transistor's emitter resistor (R11 on your layout) labeled 220k, but it should be 220 ohms.  If you really used a 220k there, I would imagine it could contribute to your problems.  Furthermore, the transistor as you've indicated it on the layout is probably backwards, unless you've come across a really oddball 2N3904.  They're generally pinned out EBC, with pins down and the flat side facing you.  I haven't traced it all out, but these are the things that jumped out at me immediately.

Andy73

Thanks for the start!  I also just saw that one of my electrolytics is 10uf instead of 100.  I'll start there....