Chauffeur OD squealing

G

Grazza

Active member
Just finished another build and I have plugged it in to see how it goes and it's not good!
Chauffeur passes sound when not on but high pitched squeal when on. I've never experienced this before. I love some input on how to trouble shoot this one.
 

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Sounds like something is shorting to the enclosure. The DC looks OK, make sure the tip lugs of your input/output jacks isn't touching the enclosure.

I assume all four pots have plastic dust covers? Are you using a metal LED bezel?


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Yes, I thought that last night, will change to a plastic bezel and see what happens. That got me on the pro 10 build too, LEDs very close to other components and was shorting on the bezel!
 
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Grazza said:
It's the jacks, works with them floating in the air. Just don't understand what is causing it. they aren't touching anything they are not supposed to
Click to expand...
That means something is touching the enclosure when you put it in the box.

The jacks are connected to ground so when you plug them in, whatever it touching the enclosure means s now connected to ground as well.

Is anything touching a potentiometer maybe? Do you have those plastic covers on all your n the pots?
 
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Yes I have the plastic covers on the pots. This has got me baffled, if i leave the jacks floating in the air, but everything in the enclosure it works, as soon as the jacks go in its just high frequency feedback sort of noise. The jacks are in a bad spot, don't follow the drill template on this one, drill them higher like on 125 builds, they are too tight with the front pots. Having said that, really can't see any metal on metal
 
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Grazza said:
Yes I have the plastic covers on the pots. This has got me baffled, if i leave the jacks floating in the air, but everything in the enclosure it works, as soon as the jacks go in its just high frequency feedback sort of noise. The jacks are in a bad spot, don't follow the drill template on this one, drill them higher like on 125 builds, they are too tight with the front pots. Having said that, really can't see any metal on metal
Click to expand...
If you are desperate you can use insulated jacks. These do not touch the enclosure
 
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just an update if anyone is interested, been re-flowing all solder joints. It went back to just noise for a while, now i have some sound through it and effect as well. not a clear as before but I can hear something. Will audio probe when I can get the opportunity to set it up. The loose connection seems possible, just can't work out where. Volume pot kinda does funny things to the noise when turned, is there a way to rule out the pot being faulty if the pot is faulty?
 
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A couple of thoughts, based on my experience:
- If a charge pump is suspected (typically a 'whining' sound), remove it and the pedal will now be operating on 9V. If the problem is resolved,
try another charge pump. If the problem is still there, reinstall the charge pump.
- In painted enclosures on high gain pedals, the bottom cover can become a ground loop if it the paint insulates it from the main enclosure.
It becomes an antenna, which picks up the output wire and feeds it back into the input wire.
- Likewise, using two 1/4" open frame jacks creates a ground loop (from the signal ground and again thru the chassis ground). Easy fix would be
to ensure both jacks are well grounded to the chassis and only send the signal ground wire to the input jack, to which the output jack will be
grounded via the chassis. I use insulated cliff jacks as the input and standard open frame jacks for the output on all my builds to avoid loops.
- Ensure continuity of the Gain and Volume jacks to ground (pin #1). 10K pots are leaking a lot of signal to ground by design and if that is
'open' the rest of the ICs are getting way more signal than expected, thus doing more amplification and 'running away.'
- Check the IC feedback resistors which determines gain, for proper values. R5, R7, R9, R15, R18
 
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Unfortunately, the problem persists regardless of whether there is a charge pump or not in there and remains the same not matter what type. I think I have to rule that out. That is some great info there that I will investigate, ground loops always seem like a mystery to me, thank you very much for that, I will keep this thread posted when I find out more, this one is a pain in the ass.
 
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Hi Andrew, when you say ensure continuity of the gain and volume jacks to ground pin #1, do you mean ensure there is continuity between pin 1 and 3 of volume and gain pots?
When audio probing I only really get a strong signal on the left lug of the pot looking at it from the back, or non shaft side. is this correct?
 
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I got as far as the gain pot with audible signal when audio probing. there was signal on pin 1 of the gain pot and nothing on the other two pins really, had to do it quietly though as everyone is asleep here. From there nothing on c4 etc.
 
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