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Microphone Ground Hum

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Microphone Ground Hum

Postby GC » Sat Oct 24, 2020 2:43 pm

Hello everyone,
Maybe someone can help me.
I'm recording with a c. 10 year old AKG C414 which has only enjoyed gentle home use, straight into an Apogee Duet and from there into a Mac.
And I'm getting some seriously intrusive low frequency hum.
I can pretty much cure this by pulling out the mains cable and running the Mac on its battery - but this isn't ideal.
However, I can also eliminate the noise by pulling the XLR connector out of the mic until there's the most minimal of contact between the cable and the mic - long before the cable lock is engaged. Any further in and the buzz returns. Obviously this a solution of sorts, but a somewhat flakey one.
Any ideas on what the actual underlying problem could be and how to fix it?
Should it be relevant, the Mac has a UK power cable which I use with an adapter because I'm in two-pin Spain.
Many thanks,
Graham
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Re: Microphone Ground Hum

Postby Hugh Robjohns » Sat Oct 24, 2020 2:47 pm

I strongly suspect your problem is a lack of a proper ground to the preamp.

Find something that is properly grounded, and wire that to something grounded on the preamp.

You might find this recent post helpful:

https://www.soundonsound.com/forum/viewtopic.php?f=24&t=74244#p711810
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Re: Microphone Ground Hum

Postby emacdave » Sat Oct 24, 2020 3:41 pm

The issue will be with the charger to your laptop (its is a laptop??) as Apple do not earth them. On the apple charger the 3 pin plug will slip off the main charge body revealing a metal "button" - if you connect a small wire from the earth pin to this "button" it will earth the laptop properly when on charge.

Hope this helps.
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Re: Microphone Ground Hum

Postby GC » Sat Oct 24, 2020 5:38 pm

Hugh, Dave
Many thanks, I was trying to resolve this from the wrong end of the chain.
I was focussed on the mic and not the Mac.
Cheers,
Graham
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Re: Microphone Ground Hum

Postby Hugh Robjohns » Sat Oct 24, 2020 5:40 pm

The critical part for earthing is really the interface, but grounding the computer properly will achieve that too, of course.
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