SOLVED Muzzle with loud high pitched Squeal

JulDP

New member
Following my post here:

https://forum.pedalpcb.com/threads/muzzle-not-working-multiple-problems.10919/post-113567

I still can't find the problem with the muzzle.
The pedal works. The Gate, Key and Passthrough all work. the signal goes through but there is a very loud 14kHz squeal.
I noticed the problem when there was no cable connected to the input jack, but after some testing I realized that the squeal is all the time there, just louder or quieter. Plugging the whole pedalboard in only makes it worse.
At first I thought the OpAmp was to blame because I tried with an audio probe and even after the first stage I could hear the squeal. I checked the resistors and (I think) they are fine and as I said I have tried several OpAmps. If it is a ground problem, I can't find it, or do you think there is a problem with the THAT4301 module?

This is a very good pedal but with this problem it is unusable :( I hope someone can help me find the problem. Any help is appreciated. I add some pictures of the build. Thanks.
 

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Just had a look at the build document, not one I've built myself, but did you follow this note correctly as below?

'TC1044S, MAX1044S, or ICL7660S can be used in the place of LT1054 for IC1. Bridge solder pads under IC1 when using any of these substitutes. Do NOT bridge pads when using LT1054.'

Also perhaps check whether you used a charge pump without an S, such as MAX1044. The ones without the S make a consistent squeal (at around 10k in my experience) and obviously can't be used for audio applications.
 
Hi mybud,

Thanks for the tip. In the past I´ve had problems with the MAX1044 also (I confused it with the MAX1044S) . But this time I'm actually using a LT1054, to be excatly the LT1054CP. Do you think this also could be a similar issue as the one with the MAX1044? I add some pictures of the ICs.
 

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Not sure, but did you double-check that you didn’t bridge the pads under IC1? That might be the cause of the squeal if they are actually joined.
 
Ok, apparently some voltage regulator ICs can be suspect depending on the supplier, I’m told. I had one installed which was supposed to supply 18V but it actually read only 15V. Try measuring your voltages on the ICs and transistors in question and post them here. Perhaps someone will spot a weird reading and advise you more exactly where the problem lies.
 
Fair enough. If you have a DMM, it’s worth measuring the various voltages and posting them. Those and the pics should provide enough info for assistance. Double-check component values too, while you’re at it, just for safety’s sake.
 
Fair enough. If you have a DMM, it’s worth measuring the various voltages and posting them. Those and the pics should provide enough info for assistance. Double-check component values too, while you’re at it, just for safety’s sake.

You're right. It doesnt hurt to double check. If I have time, I will post the values of the transistors and de IC´s today. Hopefully that could help sorting the problem out.
 
See if it still squeals if you connect your ins and outs by bypassing the footswitch altogether. That will eliminate the off-board connections as part of the problem.
 
The squeal could be a ground issue, make sure your input/output jacks have proper connection to the enclosure. Scrape the paint/power coat finish in the input/output hole to make sure you get a good grounding.

EDIT: Forget that comment, just realized your enclosure is not painted :D
 
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The squeal could be a ground issue, make sure your input/output jacks have proper connection to the enclosure. Scrape the paint/power coat finish in the input/output hole to make sure you get a good grounding.

EDIT: Forget that comment, just realized your enclosure is not painted :D
No problem, any idea is welcome! A grounding issue is one of my theories too. At the beginning I got a loud hum when I didn't ground the Key and the Passthrough. After I grounded them the squeal was still there.
 
Here are the measurements. No cables conected. The values are for the Threshold potentiometer at 0% and at 100%. I hope that helps.
 

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I finally got my hands on a new LT1054. I replaced it and.... no more squeal!! So, the last one was faulty. It was exactly the problem I had with the MAX1044 on another build. I will pay more more attention when working with this type of ICs. Well, I just wanted to put the information out. it may be useful for someone. :)
 
I wonder if your chip wasn’t genuine, in the photos it has the notch at the end of the IC, and many on google look just like your tl072 does with just the circle imprint to denote pin 1.
 
I wonder if your chip wasn’t genuine, in the photos it has the notch at the end of the IC, and many on google look just like your tl072 does with just the circle imprint to denote pin 1.
Hey Swyse, good eye! that really could be the case. Take a look at the new LT1054, circle imprint. I bought both IC's from the same store and it is reliable. Maybe it was a fake batch of IC's they had. That imprint might be a good reference to look for.

Muzzle09.jpg
 
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