Hello I have the Sparkfun mp3 shield which I love. Currently, I have the shield outputting over a 3.5mm cable which runs through a ground loop isolator. This cord is very short (<3 feet). This cable then runs to a powered speaker. This speaker is powered by a micro-usb cable plugged into a wall wart and plugged into a 110v surge protector. In other words, the speaker is powered by something totally different than the shield. Here’s the strange part. If the speaker is on and plugged into the shield but the shield (and arduino) underneath is totally powered off, there is a loud buzzing sound coming from the speaker. As soon as the ardunio/shield is powered on (not playing sound yet), the buzzing stops immediately.
I’ve tried multiple wall warts, different outlets, bypassing the surge protector, not using the ground loop isolator, etc. All result in the same effect.
Since I need to leave the speaker turned on at all times while the shield is mostly off, I need to eliminate the buzzing. Any help would be greatly appreciated.
I’m not really sure what might be causing this. It does sound like a ground loop to me but since you have a ground loop isolator installed, there could be something else that’s causing the issue.
Is the Arduino/MP3 shield connected to anything else even when off? I’m wondering if the noise may be coming from something external to those. Not sure what type of ground loop isolator you’re using, but you might try switching to a transformer based isolator like brow is suggesting. The one you have now might be more of a filter for noise than a transformer.
Also, have you tried disconnecting the Arduino from whatever it’s being powered by? Even when off, a power supply might be leaking some AC and that could be getting into the audio path.
Thanks for the feedback guys. My original ground loop was just a filter as you suggested. I purchased a 1:1 transformer and that didn’t improve it much at all.
The arduino is connected to an IR break sensor and also and IR receiver for a wireless remote. That’s it.
I tried disconnecting the arduino power source but that didn’t help.
I’m going to try a totally different approach and will keep you posted.