Rebote 2.5 nearly working

[notid]

Hello,

I've spent the last week slowly but surely debugging my first full self-etched, self-sourced, and self-built pedal. I nearly have the pedal working.

In bypass mode, everything works fine. When on, the led turns on, but the only audio that comes through is scratchy. I used an audio probe and backtracked through the circuit. Fortunately, as I backtrack, I hear the echos and everything sounds pretty good. Going backwards, it "stops" working on the input side of the 2nd 510k resistor (parallel to the 5pf cap). On the right hand side of that resistor, everything sounds good. Move it to the left hand side and it gets really scratchy/noisy. My thought is that there is some issue with the opamp, but I'm not sure.

Any thoughts? Unfortunately I'm without a voltmeter and no camera. Nothing looks solder bridged in this area. I'm hoping that since the issue area is so small it will be an easily identifiable issue.

Thanks,
Bryce

[MmmPedals]

What layout did you use?

[notid]

It's the latest tonepad one.

http://tonepad.com/getFileInfo.asp?id=98

Thanks,
Bryce

[notid]

More details: Forgot to mention two changes. I replaced the 240K resistor with a 220k 1/2 watt resistor (all I had). I also used a TL082 instead of a TL072.

I measured the volts using a voltmeter. I stuck the black lead on ground, and inspected with the red lead. The effect was on, and the guitar cable plugged in. Not sure if this is the correct way.

Volts on the TL082:
1 (bottom right, moving counterclockwise) - 6.95 volts
2 - 6.95 volts
3 - 6.62 volts
4 - 6.86 volts
5 - 7.37 volts
6 - 7.06 volts
7 - 6.8 volts
8 - 7.4 volts

I checked flipping the TL082 around, and it makes the output all totally garbled (even if i connect an audio probe directly to the output jack).

Hopefully this provides more info to help debug this situation.

Thanks,
Bryce

[.Mike]

Yeah, definitely something wrong there.  Pin 4 should be ground (0v), Pin 8 should be equal to your battery voltage, Pins 3 and 5, I believe, should be closer to 1/2 of your battery voltage.

If I were troubleshooting this, I would pull the opamp, and measure the voltages. If they are closer to correct with no opamp, and putting the opamp back in makes the voltages go wonky, I would try a different opamp. If the voltages remained incorrect, I would go over the entire board, making sure there are no solder bridges-- even dragging a razor between every single trace, just to be sure. If that still didn't fix it, I would start looking for incorrect components.



Mike

[notid]

Yeah, definitely something wrong there.  Pin 4 should be ground (0v), Pin 8 should be equal to your battery voltage, Pins 3 and 5, I believe, should be closer to 1/2 of your battery voltage.

If I were troubleshooting this, I would pull the opamp, and measure the voltages. If they are closer to correct with no opamp, and putting the opamp back in makes the voltages go wonky, I would try a different opamp. If the voltages remained incorrect, I would go over the entire board, making sure there are no solder bridges-- even dragging a razor between every single trace, just to be sure. If that still didn't fix it, I would start looking for incorrect components.



Mike

Thanks for the advice. Here are my findings. I did try a second opamp, and have a third ready as well.

Here are the voltages empty:
1 (again bottom left, square pad) - 1.15 V
2 - 1.37 v
3 - 3.8 v
4 - 0v
5 - 3.7v
6 - 1.8 v
7 - 1.5v
8 - 7.5 v

I think that these results look correct based on your feedback.

Also, the way I had the IC chip seemed backwards to me. If I flip it so that the circle on the chip lines up with the bottom right square pad, here are the voltage results I get. In this configuration, I get the noisy unrecognizable sound.

1 - 6.25 v
2 - 6.0 v
3 - 5.4 v
4 - 6.0 v
5 - 5.5 v
6 - 6.4 v
7 - 6.9 v
8 - 7.5 v

So, in both directions, the chip's voltages seem off, but seem correct if the socket is empty.

Any thoughts?

[.Mike]

I think that these results look correct based on your feedback.

Yep, closer to being correct for sure.

I did try a second opamp, and have a third ready as well.

I think it would be pretty unlikely to have two defective opamps.

Also, the way I had the IC chip seemed backwards to me. If I flip it so that the circle on the chip lines up with the bottom right square pad, here are the voltage results I get. In this configuration, I get the noisy unrecognizable sound.

The dot signifies pin 1 of the opamp. It goes counterclockwise from there, so pin 8 is directly across from pin 1. Pin 1 goes in the square pad.

My next step would be a very close visual inspection, and dragging something between every trace and pad to make sure there are no unintentional solder bridges.

Maybe someone else has some other suggestions...?

Mike

[notid]

I think that these results look correct based on your feedback.

Yep, closer to being correct for sure.

I did try a second opamp, and have a third ready as well.

I think it would be pretty unlikely to have two defective opamps.

Also, the way I had the IC chip seemed backwards to me. If I flip it so that the circle on the chip lines up with the bottom right square pad, here are the voltage results I get. In this configuration, I get the noisy unrecognizable sound.

The dot signifies pin 1 of the opamp. It goes counterclockwise from there, so pin 8 is directly across from pin 1. Pin 1 goes in the square pad.

My next step would be a very close visual inspection, and dragging something between every trace and pad to make sure there are no unintentional solder bridges.

Maybe someone else has some other suggestions...?

Mike

I will triple check for solder bridges. I've payed really close attention. It seems strange that the voltages would change by putting the op amp in the correct way. Is it possible that this has something to do with using a tl082 instead of tl072? I ordered some tl072s, and they're on the way.

Thanks,
Bryceπ

[notid]

So I check again for solder bridges. No luck. I uploaded an audio file to show what it sounds like right now.

I have the IC chip oriented correctly, but it still makes no sound. This recording is with the audio probe directly connected to the output. Is this a grounding issue?

http://brycecovertoperations.com/BustedAudio.wav

Thanks,
Bryce

[.Mike]

Did you initially put each of the two opamps in rotated 180 degrees? When you do that, you basically connect V+ to the ground pin, and ground to the V+ pin. I believe that this is highly likely to cause damage.

Use a new opamp, and make sure you insert it properly. Don't just rotate it around willy-nilly. Pin 1 goes in the square hole, period. If you are at all unsure, then research until you are completely sure.

Beyond that, I'm afraid that my debugging ideas have pretty much reached their end. Record full voltages using the method described in this topic, and hopefully someone else can come along and provide some assistance.

Good luck.

Mike

[notid]

Thought I would update this thread since I did eventually get it working. It took a lot of investigating to find it. The socket for the opamp had a lead bent over. Apparently when I soldered it I did not notice this. So the 4 pin was totally disconnected. Very frustrating, but after I fixed it everything is peachy! I just have to box it up now. Thanks for the help everyone.

[.Mike]

Huzzah! Yeah, that will do it.

I bet you won't make that mistake again.

Enjoy your delay.

Mike