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Author Topic: Humming noise in speakers?  (Read 2617 times)

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DaOld Man

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Humming noise in speakers?
« on: September 03, 2015, 09:02:19 pm »
I plugged my new AV cables into my R-Pi frankenstein and I hear a humming noise in the tv speakers.
I noticed this with the camcorder cable I was using, so I dont think it is the cable.
I had to swap the red and yellow plugs at the tv because for some reason they are swapped on the pi.
Tried swapping the yellow and white but same problem.
Sounds like humming is on both channels.
HDMI into tv has no noticeable hum.
Anyone else experience this?


Slippyblade

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Re: Humming noise in speakers?
« Reply #1 on: September 03, 2015, 09:07:55 pm »
Audio on the Pi sucks almost universally.  One of the most effective things is swap out your power supply.  If you have one with the weird block in-the line (ferrite core or something like that) that tends to make a big difference.  Ground leakage seems to be a big issue.

As far as the A/V cords, there are a couple different pinouts used on this connection.  This article (http://www.raspberrypi-spy.co.uk/2014/07/raspberry-pi-model-b-3-5mm-audiovideo-jack/) explains it well.

DaOld Man

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Re: Humming noise in speakers?
« Reply #2 on: September 03, 2015, 09:30:41 pm »
Thanks Slippy, looks like I just need to swap yellow and red. White is left audio.
I tried reversing the polarity of the ac power coming into the power supply and it helped considerable.
There is still a slight hum when on emulation station menu, but it goes away as far as I can tell, when I start a game.
I am 99% sure I kept the polarity straight all the way from power plug to the prongs on the power supply, but I could have swapped hot and neutral some where.
This may be an annoyance if using a non polarized outlet.
I may look into a 60 HZ filter for the DC output of the power supply.

DaOld Man

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Re: Humming noise in speakers?
« Reply #3 on: September 03, 2015, 09:45:36 pm »
Not too sure about the swapping of the 120 VAC wires. I might have just turned down the TV.
I will see if I have another 5 volt power supply, this one does not have the ferrite filter in the DC line.
I may have a ferrite core I can try.
I plan to do more research on this problem. If anyone else has solved it, I appreciate you sharing.

behrmr

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Re: Humming noise in speakers?
« Reply #4 on: September 03, 2015, 11:19:58 pm »
You could always try a ground loop isolator

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Re: Humming noise in speakers?
« Reply #5 on: September 04, 2015, 03:54:12 am »
That was one of the reasons I chose to USB audio sound card adapters. They are only like $5, but they helped on my setups. Didn't totally eliminate the noise, but they do reduce the noise on my stuff anyway. I hear the hum when emulation stations starts also, not sure what is up with that. If you find a solution for the hum, let us know. I have been building mini cabs and am using 5v amplifier boards, and I have found that some of them have more hum than others.

DaOld Man

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Re: Humming noise in speakers?
« Reply #6 on: September 05, 2015, 02:51:37 pm »
Ive been doing a lot of research on this problem.
I tried a few things that did not work.
Tried another power supply. Still hum.
Tried attaching an electrolytic capacitor between +5V and GND pins on the GPIO. (This rebooted the Pi, (capacitor charging made a quick short circuit), dont suggest doing this while Pi is powered up, but I wanted to see if it made any difference while listening to the hum.):  After rebooting the Pi, this didnt seem to help any at all.

I want to try a ferrite filter but couldnt find one in my junk box.
I tied a knot in the power cord between the power supply and the pi, this seemed to help some. (A knot in the cable makes a simple 60 HZ filter, although not a real good one.)

This humming problem does not exist when using the HDMI.
The hum is not really loud, and is not too bad if volume is not turned way up on the speakers (TV in my case).
I got my R-Pi NES case closed up, but I can easily take it back apart if I (or you) come up with any new ideas.

Slippyblade

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Re: Humming noise in speakers?
« Reply #7 on: September 05, 2015, 03:18:58 pm »
HDMI audio is digital, the 3.5mm jack is analog audio.  That's why you don't hear it on the HDMI end of things.  Take some solace in the fact that it's not just you or your equipment.  It's a shortcoming of the Pi itself.

DaOld Man

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Re: Humming noise in speakers?
« Reply #8 on: September 05, 2015, 03:35:09 pm »
Yeah. I hope the Pi in the sky guys (bad pun I know), will address and fix this issue on the next release of Pi.

Slippyblade

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Re: Humming noise in speakers?
« Reply #9 on: September 05, 2015, 04:42:12 pm »
I just found an interesting page.  Check this link for some suggestions.

http://www.retrobuiltgames.com/porta-pi-arcade-help/noisy-audio/

DaOld Man

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Re: Humming noise in speakers?
« Reply #10 on: September 05, 2015, 11:45:11 pm »
That is interesting. I would think that the shield from the Pi would connect to Pi's ground. Need to ohm it out and see.
I really dont see anyway to connect the ground from the Pi to the ground in the TV audio amp, unless it is through the audio cable shield.
But you have to be careful, you could set up a ground loop that would introduce more noise.