Built the IC-based Overdrive. No Sound.

Started by angelkiller, February 16, 2013, 07:15:36 PM

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Ok, so I built the IC-based Overdrive circuit in the top of this forum. I first built it on a breadboard. It worked. Then I moved it to a smaller PCB. Then it didn't work. No matter, I probably messed something up. So I built it again on a PCB. (I ordered 2 of every part) Still didn't work. Got frustrated. Took one apart and built it a third time and it still won't work. Clearly this is above my head.

No part substitutions. No idea if it's a positive or negative ground circuit. Absolutely nothing happens when everything is connected. (I have adjusted the gain and volume knobs. :icon_wink:)

Now I know the problem clearly happened when I transferred the circuit from the breadboard to the PCB. But as long as the connections are the same, it should work. I'm just trying to figure out which connections I messed up. I would give pics and voltages, but I think following my messy work would be difficult and I'm not sure what votages to give.

I do have a multimeter and I can provide whatever other information you need. Thank you in advance.


hang in there. this stuff is tricky. almost none of my pedals work right out of the gate. get that multimeter out and give us the voltages of your battery and each pin of the opamp.



Battery is 8.63v

1: 6.90
2: 4.00
3: 2.88
4: 0
5: 0.01
6: 4.31
7: 8.57
8: 0.01

Pin 2, 3, and 6 shouldn't be that... But I can't figure out what's causing the issue.

I found a bad solder connection. That fixed pin 2 and a changed the other values ever so slightly. Pin 3 still seems really low.

Hmm. I found another bad connection. Numbers are accurate now.


OK! Got it working!  :icon_mrgreen:

My problem was two connections that looked alright were actually not connected.

Now two more questions:

1. he circuit doesn't seem to work while I'm touching it... As soon as I take my hand off, it works how it should. Why is this? It's in a metal Altoids tin, but no wires are shorting. (What about the 1/4in jacks and pots? Do they have to be grounded in any way separate from the circuit?


 :-XSo, I got the first one breadboarded and working in the altoids tin. Really happy how it turned out.

I fixed the grounding issue. Two resistors were too close to each other, so I moved them and also one of the pins of the potentiometer would make contact with the altoids tin only when closed, which explained why closing the tin stopped it from working.

I built a second one on another small pcb. This one's going into a pepper can! But it currently doesn't work.

When I turn the volume up from 0, I get this 'drumbeat' noise.

1 .01v
2 4.01
3 Varies between 5.4v and 6.12v
4 0v
5 0v
6 8.65v
7 Varies between 5.07v and 6.49v
8 0v

Why are those voltages fluctuating like that?

I did have to make one part substitution, for C5, instead of a .001 uf cap, I used a 1000 nf cap. Is this an equivalent part or is my math wrong? Also, would this cause the problem I described?
Edit 1: I'm pretty sure my math is wrong... don't I need a 1nf cap? 1000nf = .1uf not .001uf. Can this be fixed without ordering any parts?

Schematic here. I found the 'layout view' at the bottom to be more useful




My cheap multimeter doesn't measure capacitance. (That's what you were referring to, no?)


use calculator i linked and learn this

0.000001uF 0.001nF 1pF
0.00001uF 0.01nF 10pF
0.0001uF 0.1nF 100pF
0.001uF 1nF 1000pF
0.01uF 10nF 10000pF
0.1uF 100nF 100000pF
1uF 1000nF 1000000pF
10uF 10000nF 10000000pF
100uF 100000nF 100000000pF

for nonpolar caps, capacity is usually declared by code ( 104J for example )  
this is how you read it:  first two digits stand for pF, so if code is 104J you have 10pF. then third digit is number of zeros to be added to this value  10(0000) pF=100.000pF=100nF=0.1uF.  "J" stands for tolerance of 5% so that means its capacity should be in range 95.000-105.000pF=95-105nF

you may also wana use this calculator for resistors http://www.dannyg.com/examples/res2/resistor.htm


Ah, I see now. Well, after a long night, I finally got it working.

First, the cap I substituted was 1000pf. Which is equal to .001uf according to what you just wrote. So I think my math was correct, but the info I gave was not.

Anyway, From looking at the schematic, I decided to elimininate the cap completely since I was under the impression I had the wrong one. The schematic didn't require much revision, but my layout had to be tweaked to get it right.

Long story short, after poking around with a multimeter and reading how op-amps work, I got it working. I had some other mistakes in my circuit. So now I've made two of these and I'm really proud.  :icon_mrgreen: I learned a bunch and already have more goodies in the mail. Thanks for the help everyone!