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I have a mackie mix8 mixer, which comes with a cheap power supply that generates a loud hum (at least I think so -- I don't have a different power supply at the moment to verify)

I noticed that if I connect the mixer to the ground (for example by touching the outside ring of microphone out with one hand, and kitchen sink with other hand), the hum goes away.

Power connection on the mixer is a standard barrel plug with 2 contacts, so apparently it was not designed to be grounded.

My question is, should I ground the mixer, and is it safe to do so?

Or should I just get a better power supply?

I'm not connecting the output to a computer or any other device, it goes into a digital recorder which is battery-powered. Input is a microphone. So I don't think this is a grounding loop issue. The hum is audible whether the microphone is connected or not.

  • I'm a little confused; does this hum come from the mixer when only the monitor speakers are connected? Which outputs are you using for monitoring and recording? Does this hum persist with only headphones connected? – Marc W Oct 27 '16 at 18:53
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it's Always a good idea to ground your equipment, audio-related or not, in your case, grounding your mixer probably gets rid of the hum, but also makes it safer to use (if for example the body (which I'm guessing is a conducting material) is being put under a current, it won't shock you because it'll redirect the power to the ground instead).

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Your symptoms describe a bad mic cable. None of your symptoms suggest that there is anything wrong with the mixer or its power supply.

  • "The hum is audible whether the microphone is connected or not..." – Marc W Oct 27 '16 at 18:42
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So, you have a mixer, which is line powered via a power brick or wall adapter, and a battery powered recorder. And with nothing else connected, you have a hum.

Assuming you have checked basic things such as making sure that any unused inputs are turned down, and the mixer is humming, there is clearly a problem with the mixer or its power supply and it should be repaired or replaced. Grounding it may make the problem go away, but a mixer in isolation, not connected to anything else, should not be humming like that.

By grounding the mixer you are only hiding the problem not solving it, and the problem may well come up again later when you start to connect other devices.

PS: You should also eliminate other variables such as the recorder and the cable connecting the recorder. If for example you do not get any hum in headphones connected to the mixer you might be connecting the recorder with an incorrect or broken cable.

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