sudomod

I'm getting a lot of background white noise using a Sabrent USB audio device and the Adafruit 2.5W amp for mono sound. Everything is working, but I'm still getting a buzzing sound. It's less distracting when sound is playing, but very apparent when not (especially in the headphones).

My power and ground are all coming from the Pi itself since I'm still checking everything before it gets set in. Could that be the issue? Any other suggestions?

This isn't a deal breaker, but if I can clean the sound up with a simple fix I would like to do so before I start glueing everything down one last time.

Pictures or wiring diagram would help us

Can you test it from a PC and use a headphone just to make sure the sound is fine?

I’m pretty sure that the distortion must be coming in from the amp or speaker. I tested using my PC sound system through the USB audio jack when I was first connecting the USB to the Pi and had no distortion.

I will be happy to upload a wiring diagram when I get a moment to sketch one out. As it stands, there is only one wire (left channel) connecting the USB soundcard to the amp via the A+ port. The A- port is bridged to the ground, which is grounded in GPIO 6 on the pi. The power for the amp is running to GPIO 2. The USB card is powered via the USB hub, which is powered via the two connections right by the pi power input.

I haven't used that set up before (I typically use the adafruit amp alone, and it is a bit noisy, but manageable), have you tried to skip the amp and just use the USB sound card to rule out if the amp is causing the noise? It may not be necessary to even have an amp at all, if it is anything like the minty pi the usb sound card drives the small speaker just fine.

Also, do you have a volume wheel, and headphones? Maybe it is a combination of all the wiring, that is causing some of the noise? And finally, the adafruit amp has a small screw pot on it, maybe lower that a bit (use a screw driver), see if it helps.

Either way, a wiring diagram will be nice, or some photo's, so we can see everything.

Here is the promised wiring diagram. If you can't tell, this IS my first rodeo:



I've left out the pot and headphone jack because the issue started before adding those components (and therefore not likely being created by them) and because I'm almost completely certain they are wired correctly.

I remember from my days of wiring up my own car sound system a similar sound being introduced by "ground loop" issues. Is that possible here, since I'm grounded in two spots on the Pi? If so, how could I best remedy that?

hmm, wiring seems fine, only suggestions I can give are (not sure if they will even make a difference):

Take the ground from the sound card (in your pics it should be the one to the left of your yellow wire, double check that) and run it to A-, instead of the bridge (Not sure if it will make a difference). You can also skip the USB hub and wire the sound card direct to the pi. Maybe it is something in the USB hub that is causing interference? That may help narrow your problem down

And in the end you will likely want to power the amp from your power source (power strip if you have one), not the pi itself.

rodocop wrote: ↑

Mon Jan 08, 2018 12:20 pm

hmm, wiring seems fine, only suggestions I can give are (not sure if they will even make a difference):

Take the ground from the sound card (in your pics it should be the one to the left of your yellow wire, double check that) and run it to A-, instead of the bridge (Not sure if it will make a difference). You can also skip the USB hub and wire the sound card direct to the pi. Maybe it is something in the USB hub that is causing interference? That may help narrow your problem down

And in the end you will likely want to power the amp from your power source (power strip if you have one), not the pi itself.

Thanks for the suggestions. I’ll try both and see what I get on the other end. I’m pretty sure it isn’t the hub because I did not get any distortion when I used the 1/8 inch jack that was originally on the card, but it’s certainly possible something went sideways after that. The ground bridge could be the culprit. I have a feeling that removing the amp will remove the distortion, but I worry about volume on the speaker.

yeah, can't hurt to remove the amp and see if sound quality is good enough. Let us know how things proceed.

Take the amp out of the equation and retest.