Author Topic: Mini Mu Help  (Read 2144 times)

jwin615

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Re: Mini Mu Help
« Reply #15 on: June 06, 2023, 07:19:47 PM »
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

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Re: Mini Mu Help
« Reply #16 on: June 07, 2023, 12:43:35 PM »
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

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Re: Mini Mu Help
« Reply #17 on: June 09, 2023, 09:08:15 AM »
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.
« Last Edit: June 09, 2023, 09:16:19 AM by benny_profane »

rhaas

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Re: Mini Mu Help
« Reply #18 on: June 09, 2023, 04:24:46 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.

jimilee

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Re: Mini Mu Help
« Reply #19 on: June 09, 2023, 06:27:05 PM »
Woohoo, nice job!!


Sent from my iPhone using Tapatalk
Pedal building is like the opposite of sex.  All the fun stuff happens before you get in the box.

rhaas

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Re: Mini Mu Help
« Reply #20 on: June 09, 2023, 09:56:46 PM »
Woohoo, nice job!!


Sent from my iPhone using Tapatalk

Thank you! Really liking how this sounds so far.

madbean

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Re: Mini Mu Help
« Reply #21 on: June 10, 2023, 05:07:09 AM »
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

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Re: Mini Mu Help
« Reply #22 on: June 10, 2023, 03:00:35 PM »
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. :)