I'm running a small class D speaker amplifier directly on my PC's ATX 12v rail (like this), so that it switches on when my PC turns on. This works great when I play music on it from my phone, but when I plug in my PC's 3.5mm jack it makes a ton of noise / hum / pickup. I'm not sure how to fix it, I hope this is enough to go on. Any suggestions are welcome.
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\$\begingroup\$ 50Hz hum is probably a ground loop issue. Have you tested with a balanced signal? What about varying the cable length (if you have different lengths)? The best way to deal with that kind of noise is to break the DC ground loop using power or signal isolation or heavy filtering \$\endgroup\$– Arthur ChassandeCommented Dec 26, 2022 at 19:39
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1\$\begingroup\$ It is unclear how it is wired. So power and audio come from single PC powered by single ATX supply? If so you may have a ground loop. Please draw the actual wiring or take a photo. \$\endgroup\$– JustmeCommented Dec 26, 2022 at 21:15
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\$\begingroup\$ Without photos and schematics, this is hard to diagnose. I've seen this kind of problem when someone plugged a 2-channel stereo headset into a 3-channel jack that was also expecting a mic connection. The mic-to-speaker cross connection created feedback. There's not enough info here to diagnose the issue and far too many possible places to look for a solution to start listing them. \$\endgroup\$– JBHCommented Dec 26, 2022 at 23:11
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\$\begingroup\$ I know it's too vague a question, thanks for trying to help anyway! I'm a little out of my dept here. I'm gonna look into the ground loop, that sounds plausible. And yes, it only goes wrong if I run both the PC generating the audio signal and the amplifier from the same ATX PSU. \$\endgroup\$– aai aaiCommented Dec 27, 2022 at 8:18
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\$\begingroup\$ I'm going to try a signal isolator, because it looks like this is the same problem I've had in the past in my car, when charging my phone while playing music using an aux cable. Thanks for the help! \$\endgroup\$– aai aaiCommented Dec 27, 2022 at 10:41
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1 Answer
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It sounds like you are experiencing some electrical interference or "noise" in your system. There are a few things you can try to reduce or eliminate this noise:
- Make sure that all of your audio cables are securely plugged in and not damaged. Loose or damaged cables can pick up electrical interference and transmit it to your amplifier and speakers.
- Try using a grounded outlet or power strip for your amplifier. This can help to reduce electrical interference from other devices in your home.
- If you are using a long audio cable, try using a shielded cable. Shielded cables have a layer of metallic foil or braided wire that helps to reduce electrical interference.
- If you are using a USB audio interface, try using a USB hub with its own power supply. This can help to reduce the amount of electrical interference picked up by the interface.
- If you are using a desktop computer, try moving your amplifier and speakers away from the computer to see if this reduces the noise. Computer components such as the CPU, graphics card, and power supply can generate electromagnetic interference that can affect your audio system.
- If you are still experiencing noise after trying these steps, you may want to consider using a noise filter or a ground loop isolation transformer. These devices can help to eliminate electrical interference by breaking the ground connection between your audio equipment and the electrical outlet.
