Stomp box enclosures and shielding

I was trying to up the quality of my builds and thought about shielding and noise. Did a little research on the interwebs and came up with a few tips.

First a little background. High gain circuits often run series of gain stages in series. If you have an input stage of x10 followed by an adjustable stage of x10 to x100 you have a minimal gain of x100 to a max gain of x1000. That’s a lot of gain. Anything that gets into your circuit at the input will also be boosted by x100 to x1000! Think of cable crackles, switch pops, scratchy volume pots on your guitar, and more.

Then there’s the noise in the air from electromagnetic interference. It’s not uncommon for pedals to pick up radio transmissions, remember that scene from Spinal Tap? Or the hum of electronic devices like fluorescent lights.

In many ways the enclosure acts as an antenna picking up electromagnetic noise. But it can also be used as a Faraday cage which can be used to protect the circuit inside from electromagnetic interference from the outside. To do this the enclosure must be connected to ground.

if you have open frame jacks like the Switchcraft jacks the sleeve will make contact with the enclosure. This grounds the enclosure for free. If you’re using those jacks with the plastic body you’ll need to run a wire to the enclosure somewhere.

Is it enough to ground the box? Yeah but in the case of painted boxes or boxes with a powder coat the bottom cover may not make an electrical connection to the main body of the enclosure. I used a drill bit to remove the paint from one of the counter sunk screw recesses. This allows the screw to make contact with back cover and main body of the enclosure.

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