My $40 expresso machine amp build had a surprising ground loop fix

I built a tiny practice amp inside a dead espresso machine last month, wired everything like my usual Fender Champ circuit. On first power up it buzzed like crazy, so I assumed the metal shell was the problem. After 3 tries of moving the ground wire around, I realized the steel inner frame was acting like a pickup and amplifying a wall transformer I had sitting 2 feet away. I moved the transformer to the floor and the buzz dropped 90 percent instantly. Has anyone else had interference from nearby wall warts on their metal enclosure builds?

2 comments

2 Comments

linda33526d ago

@davis.mia my buddy Dan had the same thing happen with a pedal he housed in an old cookie tin, drove him nuts for a week until he realized his phone charger was sitting right under the bench. He only figured it out when he unplugged everything else in the room out of pure frustration lol.

davis.mia28d ago

Wait, so you’re saying the wall wart itself was the main culprit, not the chassis grounding? Honestly, that flips my whole view on this. I used to think any buzz in a metal box meant you messed up the ground wire, full stop. Tbh, I would’ve spent way more time tearing the thing apart before even thinking about the transformer. Ngl, it makes total sense now, the steel frame basically turns into a giant antenna for that magnetic field. I’ve got a few builds in metal cases and I never even considered where the power supplies sat. Gonna have to check that on my next project, because your fix is way simpler than any rewire work I’d have planned.