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!
I'd start by pulling the three ICs off the main board then re-compare some voltages (IOW, check the pins of the bare sockets) to see if they start to align with the ones in the doc. Particularly check where you are getting -6.5v and it 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)
On the backside of the board, check for solder bridges. Also, a lot of your solder joints should be reflowed so the solder flows through the board.
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It's not that you should measure empty sockets for voltages. It's that when voltages are off by so much, it's helpful to remove the ICs sometimes to see if some problem areas are resolved. That way you may be able to identify if a specific IC is causing the issue.
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)
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?
Do you have another 134 or single opamp you can try?
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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
Is the white wire from your power jack connected to the + terminal of the switching board? I can't see from the picture.
Quote from: Bio77 on June 06, 2023, 06:26:56 PM
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).
Have the correct type dpdt on-on-on switches?
Quote from: jwin615 on June 06, 2023, 07:56:55 PM
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/
Quote from: rhaas on June 06, 2023, 08:57:49 PM
Quote from: jwin615 on June 06, 2023, 07:56:55 PM
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/
I'm driving at the moment so can't confirm anything but there are two types of dpdt on on on switches. Type 1 and type 2. The center position is inverse between the two types.
I'm not super familiar with this circuit or the circuitry around those switches to know if it could be causing any issue. Just stating an obvious but maybe not so obvious possibility.
I believe generally type one is the more common unless otherwise notated
Quote from: jwin615 on June 06, 2023, 10:53:38 PM
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. :D 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?
SBP appears to only sale type 2. Small bear link doesn't link to datasheet but found the dp7 info on another datasheet and it indicates type 2.
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!
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.
Quote from: benny_profane on June 09, 2023, 03:08:15 PM
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.
Woohoo, nice job!!
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Quote from: jimilee on June 10, 2023, 12:27:05 AM
Woohoo, nice job!!
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Thank you! Really liking how this sounds so far.
Quote from: rhaas on June 09, 2023, 10:24:46 PM
Quote from: benny_profane on June 09, 2023, 03:08:15 PM
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.
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.
Quote from: madbean on June 10, 2023, 11:07:09 AM
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. :)
Hi all,
Sorry to bring back this old thread but I currently am working with a Mini Mu and was wondering if anyone ever figured out definitively what kind of DPDT On On On switches the circuit should be using? The switches linked in the build doc are labeled by Small Bear as Type 1 in the description, but when I got them today they read as a Type 2 switch when I test them with my meter. My Mu was sounding a bit lackluster and I was wondering if I originally got the wrong switches. I have removed the original switches that I had and bought the ones that were linked in the build doc, but I am hesitant to solder these on until I have a better idea what I need. Thanks for any and all assistance!
-Justin
Well this is quite odd. I just looked over all this and my switches on hand.
Here's the trace path for the BP setting. That would seem to indicate type2. I just checked the On/On/On DPDTs I have on hand with my continuity checker and they all have type2 connection. However, they are labeled T1!! So, now I don't know what to believe as far as labeling. I have no way of knowing if these are ones I got from smallbear or Lovemyswitches.
Got mine from Tayda, it worked.
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I did a lot of back and forth between a Type 1/2 diagram and the schematic and PCB traces and also assumed it should be a Type 2 switch, but also ended up with a headache from all the flipping back and forth. I think in the name of science, I'm gonna wire up some test leads to the board and see if wiring the switch as a Type 1 or 2 gives the best results. I'll report back my findings, probably in the next few days. Thanks again everyone for your feedback so far.
UPDATE!
I finally got a chance to break out the soldering iron and get this figured out. After plenty of wiring and unwiring my findings are as follows. Type 2 switches are the way to go. The overall performance is better in this configuration with both bass and guitar. However, Type 1 switches worked too and did not seem to break the functionality of the circuit. Both switches still worked fine in the middle position, but were maybe a little thinner sounding than when wired with a Type 2 switch.
Thanks again to everyone who offered assistance!
Nice, thanks for the hard work. I know how much a pain wiring and working is.
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