What the heck buzzing, no ground, ground loop?

Thread Starter

thisguy1

Joined Aug 18, 2016
11
I made a mini PA speaker system and I'm trying to track down a buzzing.

I'm using 12v as my main PSU which runs the amp then drops down to 5v to run a sound chip but IDK what to do about the humming.

I started out using a 12V to 5V car charger for my drop down (removed casing). Then I tried using a 5V regulator with a USB socket but still got buzzing. And what's weird is if I disconnect the ground on the USB socket it still plays, but how is that possible?

Then I tried using a battery jumper that has USB output and the buzzing goes away but I can only test for 30 seconds then the jumper shuts down.

The USB on the chip is it's power and programming. Maybe it might help if I solder leads from the USB on the board to its own +/- but I don't want to have to do that.... I've tried 2 different 12v to 5 volt chargers and the regulator.
 

MrChips

Joined Oct 2, 2009
30,712
The buzz you are hearing is most likely 60Hz and 120Hz noise from the AC power line.

Your AC to DC converter needs to be super clean in order to eliminate the hum.
 

LowQCab

Joined Nov 6, 2012
4,023
Mass-produced USB devices can be quite noisy,
a Linear-Regulator is a much better bet for Audio projects.

Not all "Sound-Chips" are created equal,
most are designed to be incorporated into a Circuit with other matching Chips,
using them in a "stand-alone" manner can make them do all sorts of weird stuff.

Of course we still don't have a Schematic and part-numbers, so it's anyone's guess.
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Ya’akov

Joined Jan 27, 2019
9,070
And what's weird is if I disconnect the ground on the USB socket it still plays, but how is that possible?
You say "no ground loop" but that certainly sounds like there is a ground somewhere else since there has to be a circuit to power the device. What is that ground?
 
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