Microphonic caps

Frequently asked questions on capacitor types, ratings, brands, use and abuse.
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sirlurch
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Post by sirlurch »

I have an MXR M109 6 band eq pedal that appears to be microphonic. After poking around with a chopstick, it appeared that C2, C3, and C4 were all making noise. I traced the board out and, other than the addition of a switch and extra filtering, it is the same basic design as the old M109 schematics you can find online (just with different callout names). So I replaced these 3 caps, but the problem persists.

I also reflowed all the jack, switch, and power supply contacts in case it was a broken ground connection, as well as all the components that go to ground.

I'm about at the end of my rope. Any ideas?

Thanks!
Eric

sirlurch
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Post by sirlurch »

Guessing this should've gone in the Request folder. Apologies. I'm new here.

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plush
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Post by plush »

sirlurch wrote:So I replaced these 3 caps, but the problem persists.
Which caps did you use as a replacement? If ceramics, then what type of dielectric?

sirlurch
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Post by sirlurch »

These are 1206 SMD XR7 ceramics, so yeah, I may have replaced microphonic caps with more microphonic caps. :) But there is a big 220uF electrolytic in front of them that I'll replace next. It has a good ESR, but I'll change it out anyway. If that doesn't do it, should I look into C0G caps for the SMDs?

Thanks!

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plush
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Post by plush »

sirlurch wrote:These are 1206 SMD XR7 ceramics, so yeah, I may have replaced microphonic caps with more microphonic caps. :) But there is a big 220uF electrolytic in front of them that I'll replace next. It has a good ESR, but I'll change it out anyway. If that doesn't do it, should I look into C0G caps for the SMDs?

Thanks!
C0G/NP0 mostly
but I think the caps may not be the case here

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Dirk_Hendrik
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Post by Dirk_Hendrik »

Ceramic SMT caps can be microphonic. Bin there..
But, the only times I experienced this problem was wen using rotten amounts of gain.
Sorry. Plain out of planes.

http://www.dirk-hendrik.com

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Post by sirlurch »

plush wrote:
C0G/NP0 mostly
but I think the caps may not be the case here
Any ideas? Fumbling with DC cables or input cable produces microphonic effect. Eliminating the pedal and the rest of the board is quiet. Isolating it (using just this pedal) into amp is producing it. So then I opened it up and started chopsticking (after I cleaned the jacks with Deoxit). The loudest is coming right from the first cap after the input jack.

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Post by Manfred »

The knocking on the components is transferred to the board and case, so I think it might be due to a loose contact or a cold or broken solder joint.
Often such errors can be found on the sliders.

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Post by sirlurch »

It was the caps. Replacing with C0G and tantalum caps fixed it.

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