# SOLVED: Calamity fuzz - only working with onset on full



## sclemmer (May 8, 2021)

Calamity fuzz only works with onset control on full. Only substitutes in the build are 2m2 resistors instead of 2m. If I strum very hard I can get sound with the onset control half way up. Could this be a bad pot?
Also, no combination of the switch settings helps the issue.


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## Chuck D. Bones (May 8, 2021)

Your JFETs have the wrong Vp.  Check this thread on the Build Reports.  It's not enough to have real J201s; they have to be hand-selected.  That's what Fairfield Circuitry does.


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## sclemmer (May 8, 2021)

I’ve got 4.6v on Q1 and .5v on Q2. Is that not where I need to be? I socketed the drain resistor on Q1 but not Q2. The 201’s are legit, bought them from Mammoth probably 10 plus years ago.


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## Chuck D. Bones (May 9, 2021)

Oops, 4got to insert link in previous message.  It's fixed now.  Your JFET bias is in the ballpark.  Is your circuitboard super clean?  Flux reside could mess up the IC's operation.  Or maybe one of the diodes is backwards.  Post some pix of both sides of the board.


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## sclemmer (May 9, 2021)

Here‘s some pics:


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## Chuck D. Bones (May 9, 2021)

Your board could be cleaner.  Can you explain what you did for R13?  What else did you do that is not per the Build Docs?


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## sclemmer (May 9, 2021)

Which part of the board could be cleaner? The spots between the switches? I took the pic right after cleaning it and couldn’t get between the switches. For R13, I didn’t have a 270k resistor so I connected a 240k and 30k together. Nothing else different from the build doc.


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## Chuck D. Bones (May 9, 2021)

Can you take pix that shows the bands on those two resistors clearly?  From what I can see, looks like one of them is neither 240K or 30K.  It's not a great viewing angle, so I could be wrong.

The entire board should be cleaner.  That shiny stuff on the board is residual flux.  All of it needs to be scrubbed off with IPA and a toothbrush.  When flux absorbs moisture, it makes a conductive path.  Given that this circuit has 10Meg resistors on it, even a tiny bit of stray current can upset the opamps.


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## sclemmer (May 9, 2021)

That resistor pair is at least close, I pulled and tested it, see below. I’ll try to get the residual flux between the switches cleaned up tomorrow and re-test.
Thanks for the help so far.


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## Chuck D. Bones (May 9, 2021)

OK, that's fine.  
Clean the entire board, both sides.  Flood it with alcohol, scrub it and flood again.  Avoid getting any dirty alcohol inside the pots.


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## sclemmer (May 10, 2021)

Flooded and cleaned both sides, same issue. I’ll pull the pot tomorrow and test it to make sure there is nothing wrong with it.


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## Chuck D. Bones (May 11, 2021)

You don't need to remove the onset pot to test it.  Unplug Q2 and you can test the ONSET pot in-circuit.

Let's check a couple of DC voltages, power on, ONSET to zero:

D2 cathode
IC1-3 (try both G switch positions)
The other switches don't matter.


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## sclemmer (May 11, 2021)

D2 cathode is measuring 1.398.
IC3 switch off is 1.713. IC3 switch on is 3.54.


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## Chuck D. Bones (May 11, 2021)

The voltages you measured on IC1-3 are good.  You should be getting close to 5.1V on D2's cathode.  Maybe you're not measuring on D2?  

Check the voltage at IC1-1, it should be a little higher than IC1-3.  I think IC1-7 should either be close to 0V or 9V, depending on the switch positions.  This is a crazy circuit and trying to figure it out is giving me a headache.  Maybe someone who has a working unit can measure IC1-1 and -7 for comparison purposes.  I had one, but gave it back to the owner after I fixed it.

I should have mentioned before that the voltage on Q2-D depends on the position of the G switch.  We care about the higher voltage reading.


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## sclemmer (May 11, 2021)

Doh! I was measuring D1. D2 reads 4.90.
IC1-1 reads 1.522.
IC1-7 reads 1.521 switch down. Switch up it is 3.74.
Drain on Q2 is .437 switch down. Switch up is .425.


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## Chuck D. Bones (May 11, 2021)

IC1-1 seems low to me, maybe someone who has one can weigh in.  Do you have any more TL072's?


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## sclemmer (May 13, 2021)

Anyone out there that can get voltages from a working pedal?


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## sclemmer (May 16, 2021)

I’m starting to doubt that anyone has successfully built this pedal. Prove me wrong and post some voltages, I dare you.


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## sclemmer (May 21, 2021)

Alright folks, my issue was drain voltage on Q2. I bought an original Unpleasent Surprise. Here are it’s drain voltages with all switches off:
Q1 - 5.50
Q2 - 2.41
Adjust your drain resistors to get close to these voltages and Robert is your fathers brother.
Thanks to @Chuck D. Bones for the help here.
Now on to the Low Tide...


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