Microphone hum

[Scouser]

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

Any Ideas ?

[Drew Stephenson]

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

[James Perrett]

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.

[Hugh Robjohns]

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.

[Scouser]

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 ?

[Hugh Robjohns]

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...

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!

[Guest]

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

[Scouser]

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.

[Hugh Robjohns]

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'!

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.

[Drew Stephenson]

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.

[Hugh Robjohns]

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

Good thinking ... done!

[Scouser]

Thanks for all your help with this Hugh ( and everyone else )

Whilst I am not very technically minded, I am doing my best to try and understand all your advice.

Essentially, All I am using is the mix pre 3m into a wall socket and a microphone, so It is a very simple set up and therefore shouldn't pose to many problems, to troubleshoot.

So I have started again, from square one. The Mix Pre is plugged into a wall socket as mentioned above, the headphone amp on these things has lots of gain, and if I turn it up to 100% there is some white noise, but I am guessing that is normal ? This obviously changes as soon as you plug a mic in.

Oddly enough I am back to where I was when I first posted, ie noise only from the Rode NT3, I can't get any noise whatsoever from the KM184 ? Which is a little odd, as a while back I was getting a little noise from it, I can only put this down to a dodgy lead, which is now binned, and it is working fine with all other leads. I also have a SM7B which again is not producing any earthy noise. Could it just be the NT3 ?

Have just edited this post, as I just tried the Mix Pre on battery power and noise is gone !

I have also tried plugging unit into all different sockets around the house and get hum wherever I plug in. So is there anything can I do, given I am not an electrician ?

[Mike Stranks]

A qualified response until Hugh arrives again...

I suspect that you have a floating-earth problem as Hugh suggested a few posts back.

If that is the case then one of these: https://www.soundonsound.com/reviews/groundology-earth-connection-plug should probably solve it.

I've had various funnies like you're experiencing in the past with some kit. Having read Hugh's review of the item referenced above I bought one and it did the trick nicely.

Probably, in your situation I'd use the ring of a 3.5mm plug and attach it to an appropraite socket on the MixPre.

[Scouser]

Thanks Mike,

So are you saying I should use one of these to power the mix pre ? It is powered via usb c so would I need a usb c connector coming from the groundology plug ?

[Sam Spoons]

You need to power the mix pre in your normal manner, the Groundology plug doesn't provide power, it is a 'dummy' plug with just an earth connection (but none to the line or neutral) so that you can earth Class 2 or battery powered equipment, via a spare jack socket, to the mains earth.

[Scouser]

Sorry for my ignorance Sam, so are you saying you plug in the groundology and from that, there is a lead that plugs into the mix pre ?

[Mike Stranks]

What this device allows you to do is provide a ground/earth as there isn't one provided thru the mains plug.

So you power the MixPre as you normally do with your USB Mains Supply connected to the USB Port.

You connect your mic(s) as normal to the XLR socket(s).

You use the grounding plug to provide the ground earth. You plug the pseudo mains plug into any mains socket you like - doesn't have to be switched on. In Hugh's case he replaced whatever's attached to the other end of the 'Groundology' cable with a standard TRS jack plug with the plug sleeve connected to the single-core Groundology cable. I'm suggesting that you should use a 3.5mm TRS plug as there are some 3.5mm sockets that you're probably not using on the MixPre. But you still connect the single-core cable to the sleeve of the 3.5mm TRS plug.

Thus you then appear to have TWO mains connections. One is the USB Power Supply. The other is the Groundology (earth-only) mains plug connected to the sleeve of a 3.5mm jack plug connected to any 'spare' 3.5mm socket on the MixPre giving you the needed earth/ground connection.

[zenguitar]

I keep getting this hum in my microphone

Andy

[Scouser]

Mike, thank you so much for your reply, really appreciate you taking the time to give such a detailed response.

The only thing I am a little unclear about, is if the groundology plug comes with the required 3.5mm TRS lead from the plug, or is this something you have to make up yourself ?

Reading through Hugh's review, talked about cutting and re soldering ! This is not something I can do, so if this the case I would need some kind of work around, if that is possible ?

[Sam Spoons]

I think the plug comes with a 'press stud' type connector for connecting it to their other earthing products so you would need to modify it. To test the principle you could just take a wire (guitar cable would do fine) and touch the tip of one end to the socket nut on the Mix-Pre and the other end to either a metal chassis part of any piece of class 1 equipment (or any exposed plumbing metalwork (which should all be earth bonded but may not be).

[Mike Stranks]

Mike, thank you so much for your reply, really appreciate you taking the time to give such a detailed response.

The only thing I am a little unclear about, is if the groundology plug comes with the required 3.5mm TRS lead from the plug, or is this something you have to make up yourself ?

Reading through Hugh's review, talked about cutting and re soldering ! This is not something I can do, so if this the case I would need some kind of work around, if that is possible ?

Yes; it would be a soldering job I'm afraid.

I have a 'Groundology' plug here which I could loan you (for postage costs) to see if that would work. If it does we could then decide on a way forward. PM me if you wish to pursue...

Incidentally; there's no risk of frying yourself if you do what Sam's suggested!

[ef37a]

Just a couple of observations?
Mike, there is no guarantee that the 3.5mm jack screen shares a common, chassis connection with pin 1 of the XLR, though it probably does.

I suspect that the body of the mic is 'floating' or part of its internal screening is and so it might tell Scouscer more if he touched earth to the mic body? Of course, if the unearthed part is internally floating, that will do nothing to help.

Scouscer, please treat yourself (and indirectly us!) to a £20 Digital Multimeter. I know you say you have zero technical knowledge but such a meter will help you gain some! The first thing you would be able to do is test my first statement and check if the 3.5mm jack doe in fact connect to pin one of the XLR. The meter will also be invaluable for checking cables, batteries and even measuring audio signals.

Dave.

[Sam Spoons]

Scouscer, please treat yourself (and indirectly us!) to a £20 Digital Multimeter. I know you say you have zero technical knowledge but such a meter will help you gain some! The first thing you would be able to do is test my first statement and check if the 3.5mm jack doe in fact connect to pin one of the XLR. The meter will also be invaluable for checking cables, batteries and even measuring audio signals.

Dave.

Definitely do this, you only need to acquire a little electrical knowledge and it will repay you for life.

[Folderol]

Scouscer, please treat yourself (and indirectly us!) to a £20 Digital Multimeter.

Just want to emphasise this

It is one of those things that once you have it, in a short time you can't imagine being without it. It won't make the tea, but it will check the kettle fuse!

[Scouser]

Hi Mike,

I have tried private messaging you but seem to be having problems.

Maybe you could email me here and I will get back to you scouser1968@hotmail.com

Thanks