Domarius
Posts: 37
Joined: Sat Oct 14, 2017 1:44 am

Loud buzzing when using any USB powered speakers

Fri Apr 13, 2018 1:19 am

So, I have a 5 inch display that uses HDMI but has no audio, so I need to use the analogue audio jack on my Raspberry Pi 3.

I've narrowed the buzzing down to being reproduced whenever the USB powered Speakers and the Rasberry Pi share a common DC power source. Eg. from the same USB hub, or even with the speakers being powered from the Pi's own USB port.

This problem doesn't occur when using headphones, or speakers that have a separate AC power supply (USB powered speakers running off their own USB wall power adaptor also qualifies as a separate AC power supply and avoids the buzzing too).

I've tested with a variety of
  • stereo male-to-male audio cables
  • USB powered speakers
  • and USB hubs
all with the same terrible buzzing noise, so long as the Speakers and Pi share a DC power supply.

I recorded a video demonstrating the problem
https://youtu.be/3BQuAEt6n-U
and another demonstrating the interesting variety of noises you get with the change in screen activity
https://youtu.be/aqVYU7w5KHE

As you can see, the solution is to have two separate AC power supplies, but this is incredibly clunky.

In fact, you can reproduce the buzzing even with two separate AC power supplies - by connecting a wire between the housing of the two USB plugs of the Pi and the Speakers. So it's something to do with them sharing a common ground on a DC power supply.

I reported this back to the supplier (Little Bird Electronics, Australia) and they promised me that this product, the Pimoroni Phat DAC https://www.littlebirdelectronics.com.a ... ry-pi-zero will solve the issue. Before I throw down more money on this solution, what do you guys think? Will that Phat DAC clean up the sound? How is it different than the sound hardware on the Pi 3?

Also someone in another thread suggested it may have something to do with the composite video output on the 3.5mm jack in the Pi, but apparently having "hdmi_force_hotplug=1" in my config.txt should disable the video on that jack, and I have this line (uncommented) in my config.txt already. But perhaps I need a special kind of 3.5mm Audio/Video plug that correctly grounds out the video signal?

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Imperf3kt
Posts: 2766
Joined: Tue Jun 20, 2017 12:16 am
Location: Australia

Re: Loud buzzing when using any USB powered speakers

Fri Apr 13, 2018 1:59 am

That DAC differs from the Pi's 3.5mm jack because it is digital. The 3.5mm javk uses a PWM signal to generate sound, and as such can be considered analogue.

Digital audio is generally much cleaner.

I would have suggested you have a common 'ground loop', but that happens when you use separate power supplies that lack a common ground. In your case, it seems to be the opposite.

I can suggest, if you have the parts, to try using pins 18 and 13 to make your own audio output, similar to what I did to my Pi0
Image
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drgeoff
Posts: 9803
Joined: Wed Jan 25, 2012 6:39 pm

Re: Loud buzzing when using any USB powered speakers

Fri Apr 13, 2018 8:34 am

Repeat of your previous question. viewtopic.php?f=38&t=210380

Domarius
Posts: 37
Joined: Sat Oct 14, 2017 1:44 am

Re: Loud buzzing when using any USB powered speakers

Fri Apr 13, 2018 9:23 am

Thanks guys - yes it's more of an extension of my previous question - everything learned thus far in one concise post. Replies had dried up there so I thought I'd take a shot on a different sub forum.

Well, I don't have the parts to make my own sound hardware, but if someone were able to tell me "Yep, a digital sound card thing would solve your problem" then I would go buy the part. If we're uncertain, then I'll hold off buying it for now... I can't afford to throw money around as a gamble just yet.

But I keep thinking - why is it so hard to track down the people who made this piece of hardware and get them to tell me what's going on here and what to do about it? Surely they know how it's wired up and why it'd do this?? But the forums are all I can find...

Domarius
Posts: 37
Joined: Sat Oct 14, 2017 1:44 am

Re: Loud buzzing when using any USB powered speakers

Fri Apr 27, 2018 4:38 am

Okay after asking around on some electronics forums, we finally found the solution. It was a ground loop issue, and easily fixed with this product, a ground loop isolator with 3.5mm connections;
https://www.jaycar.com.au/ground-loop-n ... m/p/AA3086

You connect it directly to the Pi's audio socket and connect the speakers to the other end - problem solved, 100%

Thank you everyone for your help along the way, it is much appreciated. I hope someone else is able to stumble across this and avoid the hassle I went through.

AbhiTronix
Posts: 6
Joined: Sun Sep 02, 2018 3:04 pm

Re: Loud buzzing when using any USB powered speakers

Fri Dec 28, 2018 5:49 am

So everyone is stuck here. Since I'm graduated from Electronics branch. I can answer this properly.

So, What is the problem? :roll:

It's a problem of Ground Loop Hum Noise, Happens when two points of a circuit both intended to be at ground reference potential have a potential between them. It causes current to flow in the ground since two points are at different potentials which is a major cause of the noise, hum, and interference in audio, video, and computer systems.

How to avoid this problem in the first place? (Easiest solution):

:arrow: Simply connect the devices(source and slave devices) to a common power outlet, or more preciously :arrow: power your USB Bluetooth speaker from any of the USB ports of your Raspberry Pi, in this case :idea: . No need for extra gadgets/parts like one mentioned above. :D

Hope this will help anyone who's affected with this problem. Kudos :)

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Imperf3kt
Posts: 2766
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Location: Australia

Re: Loud buzzing when using any USB powered speakers

Sat Dec 29, 2018 9:42 am

How does one power a usb Bluetooth speaker from a Pi? It's wireless and not related to the issue here.
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JamesPi123
Posts: 111
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Location: Inside my Pi
Contact: Website

Re: Loud buzzing when using any USB powered speakers

Sun Dec 30, 2018 6:43 am

Imperf3kt wrote:
Sat Dec 29, 2018 9:42 am
How does one power a usb Bluetooth speaker from a Pi? It's wireless and not related to the issue here.
(plug it into a USB port?) The bluetooth speaker won't have the issue because it is woreless and the only electrical connectionis via the USB port

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Imperf3kt
Posts: 2766
Joined: Tue Jun 20, 2017 12:16 am
Location: Australia

Re: Loud buzzing when using any USB powered speakers

Sun Dec 30, 2018 8:19 am

Oh, I see what you mean, you're suggesting to use a Bluetooth speaker (possible one that uses its own USB dongle - because the Pi has built in bluetooth)
While this does avoid the problem, it does not solve the issue, which has been pointed out, is a ground loop.
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