Crackle in Bass Big Muff

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griefless
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Joined: 14 Jun 2024, 17:37

Post by griefless »

Hello,

I am trying to diagnose and hopefully solve an issue with crackle on a big muff pedal I have. I am new to the world of analog electronics and have built and modded only couple of pedals.

The problem is, the pedal produces random popping and crackling along with static. This only happens when the tone knob is turned up. Level & Sustain do not affect the frequency of the crackle, only the Tone knob causes this. For what it is worth, I poured 91% isopropyl alcohol into all of the pots and turned them back and forth a bunch of times to try and clean out any gunk.

You can hear what I'm talking about here: https://drive.google.com/file/d/1bXXJ17 ... drive_link. I turn up the Tone knob about 4 seconds in and then stop touching it, turning it down at the end.

Based on a schematic created by Dylan159 and G. Bisson (huge shout out to these folks for putting the schematic together viewtopic.php?t=31296)
https://drive.google.com/file/d/1hiQqpB ... drive_link
I am lead to believe that the issue is around the circled area (pointed at by blue arrow). Like, could this be an issue with C9/C27 or R5? Or is there another place I should look?

God gifted me with shaky hands so I want to get advice before I try to deal with SMDs.

Thanks for any help.

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mauman
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Post by mauman »

Welcome to the forum!

To my ear, this sounds like a bad connection causing the popping. It could be anywhere between the input and output, but since you hear it only when the Tone pot is turned up, I would suspect that pot or the surrounding connections on the clockwise terminal of the pot, like C1, C2 and R3. This path is more audible when the pot is turned up. It could be the pot itself, sometimes you can clean the wiper and track with alcohol, sometimes you can't.

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griefless
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Post by griefless »

Thanks! I'll try replacing the pot first and see if that fixes the issue.

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Miksola
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Post by Miksola »

The connections around the pot's clockwise terminal or the pot itself would raise suspicion in my mind.
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inspectcyclist
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Post by inspectcyclist »

The issue seems to be specifically relatedtunnel rush to the Tone control, so I would start by closely inspecting the Tone potentiometer (pot). Check for any signs of damage, corrosion, or wear on the pot itself and the solder connections.

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plush
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Post by plush »

Is it just me, or the tone pot is DC coupled?

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