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Microphone hum

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Microphone hum

Postby Scouser » Wed Aug 05, 2020 1:43 pm

I have a Rode NT3 which seems to have a hum, which goes away when I touch the mic ?

Any Ideas ?
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Re: Microphone hum

Postby blinddrew » Wed Aug 05, 2020 1:46 pm

Sounds like an earthing issue. What's it plugged into and what else is plugged into the rest of the system?
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Re: Microphone hum

Postby James Perrett » Wed Aug 05, 2020 2:24 pm

Have you tried a different mic cable? As Drew says, it sounds like an earthing problem and the mic cable would be the first thing to check.
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Re: Microphone hum

Postby Hugh Robjohns » Wed Aug 05, 2020 2:43 pm

Agreed. Definitely an earthing problem.

It is worth checking the cable, although if you're running the NT3 on phantom power, the cable screen must be intact since it provides the return path for the phantom supply.

I suspect this will turn out to be another of those earth-less systems -- battery-powered laptop, bus-powered interface... etc etc... nothing properly grounded in the system.

So please let us know exactly what is connected to what in the system, and how they are powered.
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Re: Microphone hum

Postby Scouser » Thu Aug 06, 2020 10:19 am

I am plugged in to a Mix Pre 3M which is being powered by the mains. I tried it on my KM184 and noise goes away ?
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Re: Microphone hum

Postby Hugh Robjohns » Thu Aug 06, 2020 10:46 am

I can't remember, but I suspect the mains power unit for the MixPre is a class-2 (double insulated type -- look for the box-within-a-box symbol on the line lump power unit). If that's the case, then you have a floating system -- by design.

Well designed equipment using balanced connections shouldn't have a problem working in a ground-less system. Planes manage it, after all... :lol:

But not all equipment is designed as well as it should be and I suspect the NT3 has a bit of an internal grounding problem -- to be fair, it is very easy to engineer a situation where the connection between mic's outer metal shell and the XLR pin 1 acts as an aerial to RF and I am aware of a couple of other Rode mics that have had this problem. In a fully grounded system -- which is most of them -- it's not an issue, but in a ground-less system external RFI can get into the audio electronics of the mic and thus becomes audible.

This is confirmed by swapping to the Neumann mic and the problem going away -- Neumann's long history serving European broadcasters means they know very well how to engineer to exlude RFI!
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Re: Microphone hum

Postby Argiletonne » Sun Aug 09, 2020 4:34 am

cool so all you gotta do is go to a magic store, buy a finger and tape the finger to the mic, problem solved.
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Re: Microphone hum

Postby Scouser » Thu Sep 17, 2020 9:39 am

Ok, so it's been a while since I last posted,

The noise is actually there on the KM184 after all. So I'm guessing this is some kind of grounding issue, can anyone give me some possible solutions so I might eliminate this problem.
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Re: Microphone hum

Postby Hugh Robjohns » Thu Sep 17, 2020 11:33 am

Scouser wrote:The noise is actually there on the KM184 after all. So I'm guessing this is some kind of grounding issue, can anyone give me some possible solutions so I might eliminate this problem.

It's always 'some kind of grounding issue'! :lol:

In general, systems need to be grounded, but grounded in only one place... and the challenge is to work through the equipment and wiring to establish a coherent and practical grounding solution.

I can't give you solutions because I don't know what's in your system or how it's wired up... but i can give you some suggestions and techniques to find and solve any problems.

The first is to make sure everything is powered from a single wall socket via a star arrangement of mains distribution boards. And make sure the most power-hungry devices are plugged into the sockets closest to the wall socket. That minimises the potential ground-loop area.

Also, make a note of which items of equipment are class-1 (with a mains safety earth connection) and which are class-2 (double insulated, and ground-less), as you'll need t o know when it comes to solving problems later.

Ground-loop noises can only exist between Class-1 devices. Ground-less noises (which can appear very similar) can only exist in systems comprising all class-2 equipment!

Next disconnect everything and then work through methodically reconnecting each item, listening for unwanted hims/buzzes as you go -- and if you find any, resolve them before connecting anything else.

Use balanced connections everywhere if possible, and treat any unbalanced connections with suspicion as they will almost always require some special attention!

I'd start with the core system of computer, interface and monitor speakers. Make sure that's quiet and hum-free first. Then add other items, checking as you go until you have the full system again.
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Re: Microphone hum

Postby blinddrew » Thu Sep 17, 2020 12:20 pm

Is it worth copying this ^^^ post into a new thread on the useful info forum?
Then we can just point people at it as a starter in the future.
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Re: Microphone hum

Postby Hugh Robjohns » Thu Sep 17, 2020 12:33 pm

blinddrew wrote:Is it worth copying this ^^^ post into a new thread on the useful info forum?

Good thinking ... done!
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