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3. I will break mine out and recheck those voltages. I definitely have made mistakes from time to time on recording voltages so it is entirely possible I messed up. So sorry it caused you frustration.

All good! It was totally worthwhile for the fun I'll have with this thing.

Woohoo, nice job!!


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Thank you! Really liking how this sounds so far.

IC1 pin 5 is NC and shouldn't have any voltage on it and it's left floating. The build doc lists pin 8 as 'ignore'—it's a part of the offset nulling with pin 1, which aren't being used here.

Brian: Are the voltages listed in the build doc correct? Those don't seem right to me.

Update: mystery solved! 🎉 It dawned on me that after swapping the optocouplers out of desperation (with the OPA134 installed), I didn't bother to actually plug the thing in and play it because I thought the IC1 voltage readings were still wrong. The readings were closer to matching the build docs with the CA3130EZ, so that's when I gave it another spin and first noticed that the envelope effect was working.

Well... I just put an OPA134 back in and despite the voltages being "wrong" relative to the build doc, the thing works! No scratchy noises on the volume knob either. So a summary of the actual issues I encountered:
1. I missed a solder joint on initial assembly.
2. I either mis-oriented a NSL-32R3 on initial assembly (or installed a defective one... but probably the former).
3. I got kind of thrown by the IC1 voltages in the build doc, which don't seem to be correct.

One breakthrough, though the mystery continues...

I didn't think I had any other single op-amps on hand but then I realized that I had a CA3130EZ. I popped it in and that solved the voltage readings on pins 1 and 5 of the IC! Pin 6 was still off (more on that later) but I figured I'd plug in and give it a shot.

The pedal basically works now. I built a Naughty Fish a few years ago so I'm familiar with what to expect from all the knobs and switches. I noticed a bit of extraneous interference-type noise which was probably just due to the open enclosure. However, there's a lot of scratchy/static noise when I turn the level knob. Maybe this is related to the fact that I'm seeing DC voltage (~4v depending on level knob setting) on pin 6 (output).

So two questions remain:
1. What's the likely source of the DC voltage on pin 6, and is there any chance this is related to the CA3130EZ substitution?
2. How in the world did I end up getting two OPA134s from Mouser that didn't work correctly? I've ordered parts from them for years without encountering this kind of problem. I can't imagine that these are fakes (see pictures).

Thanks again, everyone!

Type 1 and type 2. The center position is inverse between the two types.

I'd love to get to the root of this, as painful as it would be to remove and replace those switches. The switches I got from SBP are advertised as Type 2. I don't see a particular type specified in the build docs, but this thread suggests that Type 2 would work (unless I'm misinterpreting the diagram posted there, or the picture on the Small Bear product page that @jjjimi84 linked).

https://www.madbeanpedals.com/forum/index.php?topic=30743.0

@madbean Do you know if Type 1 or Type 2 is correct?

Have the correct type dpdt on-on-on switches?

Just checked and I can confirm that Mode and Range are on/on/on, and Drive is on/on.

EDIT: These are the on/on/on switches I used: https://stompboxparts.com/switches/dpdt-toggle-switch-on-on-on-pcb-pin-short-bat/

Is the white wire from your power jack connected to the + terminal of the switching board?  I can't see from the picture.

Yes, it is (specifically, the square pad all the way to the left).

I have one spare OPA134 and I'm seeing the same values with that chip. They're both from the same Mouser order, so maybe they're both defective (seems unlikely) or I ordered a subtly incorrect part (somewhat more likely ).

https://www.mouser.com/ProductDetail/Texas-Instruments/OPA134PAG4?qs=7nS3%252BbEUL6vHBXizjGOrwg%3D%3D

Update: I double-checked all resistor & capacitor values, removed the pots so I could inspect and reflow all solder joints, reinstalled the pots, double-checked the optocoupler orientation, and even tried a second pair of optocouplers... and I'm still seeing largely the same voltages as the ones in my last post.

The two discrepancies that seem the most suspicious to me are the reversed polarity on pin 1 of IC1, and the 0V reading on pin 5 (which should be ~-8.4V). Do either of those point to a specific area where I could focus my troubleshooting?

Thanks, all! I inspected the board and couldn't find any solder bridges. However, I did see that I missed one of the socket pins for the TLE2074, so I soldered that (and reflowed anything that looked like it could use it). I'm now getting sound when the pedal is engaged, though the envelope effect is barely noticeable and the up/down switch doesn't seem to make a difference. Here are my new voltages with ICs installed. In summary the TLE2074 seems fine, the LM358 seems fine except for pin 2, and the OPA134 has a few anomalies (pins 1 and 5, in particular). Any ideas?

IC1 OPA134
1   8 (should be -8.4)
2   0 (should be 0)
3   0 (should be 0)
4   -8 (should be -8.4)
5   0 (should be -8.4)
6   0 (should be 0)
7   8.3 (should be 8.8)
8   8 (ignore)

IC2 LM358
1   7.1 (should be 7.57)
2   0.03 (should be 2.24)
3   4.1 (should be 4.35)
4   -7.9 (should be -8.44)
5   0.02 (should be 0.027)
6   0.03 (should be 0.03)
7   0.5 (should be 0.36)
8   8.3 (should be 8.8)

IC3 TLE2074
1   0 (should be 0)
2   0 (should be 0)
3   0 (should be 0)
4   8.3 (should be 8.77)
5   0 (should be 0)
6   0 (should be 0)
7   0 (should be 0)
8   0 (should be 0)
9   0 (should be 0)
10  0 (should be 0)
11  -7.9 (should be -8.4)
12  0 (should be 0)
13  0 (should be 0)
14  0 (should be 0)

Ah, thanks! I didn't realize these were supposed to be the measurements without the ICs installed.  :) The new measurements:

IC1 OPA134
1   0 (should be -8.4)
2   -0.3 (should be 0)
3   0 (should be 0)
4   -8.9 (should be -8.4)
5   0 (should be -8.4)
6   -2.7 (should be 0)
7   8.9 (should be 8.8)
8   0 (ignore)

IC2 LM358
1   0 (should be 7.57)
2   -4.2 (should be 2.24)
3   4.4 (should be 4.35)
4   -8.9 (should be -8.44)
5   0 (should be 0.027)
6   - 5.8 (should be 0.03)
7   -5.7 (should be 0.36)
8   8.9 (should be 8.8)

IC3 TLE2074
1   -2.9 (should be 0)
2   -2.9 (should be 0)
3   0 (should be 0)
4   0 (should be 8.77)
5   0 (should be 0)
6   -2.9 (should be 0)
7   -0 (should be 0)
8   -2.8 (should be 0)
9   0 (should be 0)
10  0 (should be 0)
11  -8.9 (should be -8.4)
12  -2.8 (should be 0)
13  0 (should be 0)
14  0 (should be 0)

Hi!

I just built a Mini Mu and I'm having some difficulty figuring out where I went wrong. The pedal powers up and switches on/off correctly, but when it's on, no sound comes through (I do notice some scratching noise when I turn the Level pot, but no actual guitar signal). Here are the voltages, and I've attached some pictures.

IC1 OPA134
1   8.2 (should be -8.4)
2   -0.3 (should be 0)
3   0 (should be 0)
4   -8.2 (should be -8.4)
5   0 (should be -8.4)
6   7.5 (should be 0)
7   8.5 (should be 8.8)
8   8.2 (ignore)

IC2 LM358
1   -0.97 (should be 7.57)
2   4.2 (should be 2.24)
3   4.2 (should be 4.35)
4   -8.2 (should be -8.44)
5   0 (should be 0.027)
6   - 0.95 (should be 0.03)
7   7.2 (should be 0.36)
8   8.5 (should be 8.8)

IC3 TLE2074
1   -6.5 (should be 0)
2   -6.5 (should be 0)
3   0 (should be 0)
4   -7 (should be 8.77)
5   0 (should be 0)
6   -6.3 (should be 0)
7   -6.5 (should be 0)
8   -6.3 (should be 0)
9   -6.5 (should be 0)
10  0 (should be 0)
11  -8.2 (should be -8.4)
12  -6.5 (should be 0)
13  -6.5 (should be 0)
14  -6.5 (should be 0)


Any help is greatly appreciated!