Center stage reverb debug

[Josemitejam]

Hi all,

When I plugged this in I had no signal with the pedal turned on, and signal came through with the pedal switched off. The LED didn't light up either. I probed around and I have a signal at r12, c3, r8 and at IC1 leg 3. But then that's it, nothing for the rest of the pedal. I've checked my component values and they look good. I've tried multiple TL072 chips there as well.

This is, admittedly, a bit of a sloppy of a build for me. I used a lot of sockets so I could play with values based off of Mark Hammer's previous suggestions. And the wiring wasn't very planned out on my end.

Here's some info that may help, or things that I wonder about:

1. The ic chip is a TL072IP, the IP shouldn't matter, correct?
2. I didn't have a 25pf so I used a 10, 10 and 4.7 of ceramic caps in parallel.
3. The 4.7 ceramic cap looks like it has another decimal.... Like this: 4.7., is that ok?


Other than that, I've check the connections especially at the sockets and that seems good, no solder bridges I can find.

Any thoughts? Suggestions?

All advice is appreciated!




Link to schematic and layout:

http://www.generalguitargadgets.com/pdf/ggg_sc_verb_mod_sc.pdf

http://www.generalguitargadgets.com/pdf/ggg_sc_verb_mod_lo.pdf




Pics:

[PRR]

Voltages?

Signal tracing?

[fowl]

You're using all 3 lugs of a stereo input jack, and I think all 3 lugs of the DC power jack, yet there's no battery snap.

[Josemitejam]

Sorry, the battery snap is there, I taped it up with blue electrical tape since I'll be using the dc jack.


Ic1
1: 0
2: 0
3:0
4: 0.05
5: 0
6:0
7:0
8:0

Ic2
1: 0
2: 0
3: 0
4: varies
5: 0
6: 0
7: 0
8: -0.05

Ic3
1: -0.04
2: -0.04
3: 0
4: -0.05
5: varies
6: -0.02
7: 0
8: -0.05

Thanks for the quick responses already!


Joe

[ElectricDruid]

The voltages tell us that no power is getting to the PCB. At all. A few millivolts on the meter is just random noise.

Check the power jack, and the power wiring, and see if you can't get 0V and 9V to the board. IC1 pins 4 (gnd) and pin 8 (9V) is a good place to check.

[Josemitejam]

Thanks! I'm going to check that out tonight. That's still true even if I'm getting a guitar signal with my probe at r12, c3, r8?

[Josemitejam]

Got it! The ggg layout was missing a ground connection - easy fix from there. Thanks a ton for your help!

Joe

[ElectricDruid]

Nice work, Joe! Isn't it great when you find it?!? 

To answer your previous question, yes, you can get signal on R12, C3, and R8 even with no power because all those components are linked directly to the input. You can follow this line through on the scematic. C3 is a capacitor, and that's a passive component that needs no power, so it can pass signal from one side to the other (from the top of R12 to the top of R8) even with nothing switched on. The signal stops after that because we get to IC1a, the first op-amp, and that *definitely* needs power!

[Josemitejam]

Ok interesting - I never knew that but I had that hunch last night that that might be the case. And yes, it is one of the best feelings! Thanks again for your help and knowledge!