Mini Mu Help

[jwin615]

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.

[rhaas]

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!

[benny_profane]

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.

[rhaas]

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.

[jimilee]

Woohoo, nice job!!


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[rhaas]

Woohoo, nice job!!


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Thank you! Really liking how this sounds so far.

[madbean]

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.

[rhaas]

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.

[Funkasaurus]

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

[madbean]

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.

[jimilee]

Got mine from Tayda, it worked.


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[Funkasaurus]

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.

[Funkasaurus]

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!

[jimilee]

Nice, thanks for the hard work. I know how much a pain wiring and working is.


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