Sound amp hum :(
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Hey guys, nice little community you have here.
Currently I am finishing up my bartop and have just hooked up the amp to find it has a nasty humming/hissing sound. I have used a little 3w stereo amplifier based on the PAM8403 Amplifier IC . it has power +/-, line in +/-/gnd and speakers out left and right +/-. Power is supplied from the pi's standard 2500mA power adapter via a set of termainals. It powers both the pi and the amp. Does it likely have anything to do with it being class D or maybe crappy un-shielded cables? I tried using a separate power source but it was worse...
Cheers
Cam -
I had the exact same issue and for me it was a grounding issue. I grounded my amp by running a wire from a screw on the back of the amp to a VGA connection on the monitor I'm using and the hum stopped. I assume the amp was previously grounded through the audio cables themselves, to the RPi, which is then grounded to the HDMI port on the monitor. The monitor is the only thing that has a grounded power supply.
To test if this is the same issue for you, you can touch your amp (try any bare metal parts), and ground yourself. If the hum stops or lowers in volume, it's a ground issue. If you have wire kicking around, that would be an easier/better test.
Another option is to get a ground loop isolator for audio. I considered this a last resort because I'd prefer to actually ground the amp instead of just filtering out the signal along the audio line.
You can also try looking at the wiki here: https://github.com/retropie/retropie-setup/wiki/sound-issues
The white noise fix listed there didn't work for me. It fixes a different problem - one that I didn't have.
USB to 3.5 mm audio is also another possible solution... but it didn't work for me. I kept it though because I have read that the audio quality is better than the 3.5 mm jack on the pi.
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Thnaks. I just tried earthing the dvi connector to the gnd wire coming from the pi and it did reduce it some. I'll solder some wires up and see how that goes. I did notice the sound was also really choppy so I changed the driver to sdl and rate to 44100 but now lost all sound in fba. I'll start a new topic for that I guess. Thanks again
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You need to explain how you have everything connected for me to comment more...
Is your amp grounded at all...?
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@Concat said in Sound amp hum :(:
USB to 3.5 mm audio is also another possible solution... but it didn't work for me. I kept it though because I have read that the audio quality is better than the 3.5 mm jack on the pi.
Just curious, what didn't work? I also took this route and it's working fine... and yeah, it'd be an understatement to just call the quality "better". I only play with libretro and mupen64plus, though, so maybe I'm just avoiding a roadblock you ran into.
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I just meant that it didnt get rid of the audio hum. There was still a ground issue even when using usb audio.
Only thing that solved it was grounding the amp. I actually tried two different amps and both had the loud hum. Ground signal must have been going through the audio cables.
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Yea this is a bit of a pain. The noise is still there and is directly related to what the pi is doing. For example in the blue and white setup screens the sound is minimal. Back out in emulationstation and its bad again. You can hear it change noises when the screen is changing or the pi is loading etc.
My amp is a circuit board so doesn't have a metal case. My setup is mains into a set of terminals then out to the pi's little wall transformer which feeds another set of terminals. I get 5v from here for the pi and for the amp. Input on the amp is simply 5v and ground. From the pi I take the 3.5mm jack to the amp which is soldered left, right, and ground. The screen which is DVi is plugged into a hdmi/DVi adapter.
I have soldered a wire between ground on the amp, from pi's audio out to the hdmi/DVi adapter. This made a difference but not much.
I'm wondering if it's a combination of a noisy power supply and grounding. I will Prob give an atx power supply a go so that I also have 12v for the light strip there as well.
Have also ordered a usb audio out but not sure that'd change anything. Powering the amp directly from the pi also has no change :s
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@Concat said in Sound amp hum :(:
I just meant that it didnt get rid of the audio hum. There was still a ground issue even when using usb audio.
Only thing that solved it was grounding the amp. I actually tried two different amps and both had the loud hum. Ground signal must have been going through the audio cables.
Ah, we are talking of differing hums, then. I'm speaking of the terrible noise you get when you--say--plug headphones straight into the Pi. It absolutely disappears with a USB sound card.
@camo200sx: I suspect based off your last comment that you are hearing the crap I am. It might be worth trying a USB sound card. $6 might save a lot of hassle.
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