60 cycle hum - help!

kiddakota

New member
i just moved into an older house and just one of my microphones is picking up 60 cycle hum. it's a tube condenser mic built by scott hampton and it's of the highest quality.

none of my other mics are picking up any 60 cycle hum. i just purchased an eb tech hum eliminator and it did not solve the problem.

any thoughts on how to fix this would be much appreciated.
 
Are your other mics dynamic? If so, it's probably getting the hum from the phantom power source. I'd check your cables too, make sure they're not near mains or transformers etc. If all else fails, you can just stick in a very fine notch filter and the hum will just disappear!!
 
some of mics are dynamic but i'm also using an at 4060 which is a tube condenser and it's dead quiet. no mains or transformers near my cables and i've tried multiple outlets in the house with no success. what kind of filter would you suggest?
 
any EQ that's handy to be honest. You just want a really narrow frequency band, i.e. a high 'Q' and set the center frequency to match the hum frequency and take as much gain out of it as your EQ will let you!!
Does hummy mic have a seperate power supply or anything odd like that? The bulletproof test is to try it on a different mains supply. I.e. a completely different building. If it still hums, then it's probably a problem with the mic's power supply, and if not then it's got to be something to do with the original location or how it was installed.
Sorry I can't be any more specific. Let me know how you get on trying it elsewhere.
Andrew
(if you still have trouble, feel free to PM me or respond here, either works!)
 
If and when you do try it somewhere else, make sure you check the 4060 too, just to be 100% sure that mains supply is clean too)
 
You can try running a ground wire from the mic's PS case to some other gear...like the preamp (or anything in your racks), and see if that takes it out. Just make sure it's bare metal to bare metal. I usually pick a screw on the case, then scrape the paint off under the screw head (it's a very small amount, and the screw head will cover it).

Get a real long piece of wire...connect to the PS case...and then just touch various cases of your other gear...you may find one connection that solves the problem. I've used this grounding "trick" a few times on my rack gear....and even on my guitar pedals.

Since you say it's an older house...at some point you may want to check all the wiring for proper Hot/Neutral/Ground connections, and for any loose wires at outlets. Remember...electricity can kill you...so be careful. ;)

Is the PS plugged into the same outlet as your AT4060 PS and your other gear...?
If yes...try moving to a different outlet...if no...plug in same outlet...etc. You have to experiment a little.
 
You can try running a ground wire from the mic's PS case to some other gear...

At the risk of being controversial, I feel compelled to say: Please be really really careful if you decide to do this. If there is a fault in either of the two pieces of equipment you connect together, and/or you earth something that isn't supposed to be earthed (like a guitar pedal) to something that is (like an amplifier), then it can be really dangerous. Even if the chances of a fault being present are small, it's not worth the risk to get rid of a single tone, which you can easily get rid of a notch filter in an eq plugin. It takes maybe 5 seconds.

(Sorry for being a party pooper, but my conscience wouldn't allow me to just let it go.)
 
Well..if there is already fault, he's going to find out about it before ever trying an external ground wire...
...like the minute he touches that mic! :eek: :D
Star grounding is common in a studio environment...that's all I'm saying he should basically do (which I'm sure you know), and it's easy enough to see what if any voltage there might be at the case (to see if there was a ground fault) with a simple DVM.

I don't care for the notch filter approach as it doesn't solve the problem...it only "filters it". ;)
 
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what interface are you using, and are you on a laptop?

i ask because some of my mics buzz using mbox and dell vostro.
The mics that buzz are grill modded mics (nt1a and oktava mk219s)

They don't buzz if i ground the mic body or laptop body to mains ground.

I made up a cable that connects spdif shield to mains ground pin to work around this problem.
I've since bought a motu 828 mk2 that doesn't suffer from this issue, thankfully.
 
Star grounding is common in a studio environment...

True, but we're not talking about a studio. It's an "older house" (which means no RCD's either) with either suspect mains or suspect equipment, or hopefully and most probably it's just hum being induced on the mic cable. Even in a studio, it's really bad practice because to re-earth kit through other kit, because if you happen to connect two bits of kit on different phase power supplies (fortunately this is HUGELY unlikely, and you need to try quite hard to do it) star grounding won't help you if the one of the cases becomes live from a fault.

I do hate myself for being 'that guy' and having to say all this so I'm reeeeally sorry for coming across like that, but "then just touch various cases of your other gear..." is just not a solution. You say you don't care for the filter approach as it's not a solution, well at best re-earthing a PSU puts off the problem, it definitely doesn’t make anything any safer, and at worst it could be lethal.

I totally see that the required situation to arise for there to be an unknown fault in one or two bits of kit is unlikely, usually you would notice something before. But my point is that I just have difficulty seeing how re-routing the earth is a good solution, because however you look at it you’re not making it safer. Surely the safest thing is to find where the hum is being induced, and if it’s not being induced then to get the equipment checked? Which as I understand it is what kiddakota is asking how to do, which is why I suggested trying a completely different mains supply.

I don’t see why given the choice, taking any sort of risk with mains or even just a PSU is a good idea.

Once again, I apologize most profusely for seeming to have my 'safety hat' welded on to my head today.
 
I did suggest he check out his "old house" wiring...and also said he should be careful. :)

That aside and assuming there are no actual faults causing the problem, rather just a typical ground loop due to how gear is internally designed/wired (audio/circuit ground VS chassis ground)...connecting a ground wire from case to case is a common and SAFE operation.
There is high-end gear with provided ground posts that allows you to do just what I am suggesting...some even gives you the option of connecting to either audio/circuit ground or chassis ground via those posts.

Nothing will burn up and no one will die if initially the building wiring is checked and the equipment is checked for fault.
You can't always *fix* things if it's somehow inherent to the design of the gear and not an actual *fault*.

But keep your saftey hat on...nothing wrong with that. ;)

Here's a quote from my Manley/Langevin Laboratories DVC manual:

We have a few terminals on the back panel for various "ground schemes". The CIRCUIT GROUND is the same ground as the electronics in the Mic Pre while the CHASSIS GROUND is the same as the steel enclosure that is bolted to the rack and is also connected to the "third pin AC Mains Ground. Both terminals are normally connected together with a small "ground strap" but this strap can be moved to the side and wire can be attached to the terminals. These are "MINI BANANA" style and will not accept regular size bananas found on electronic test gear. Be careful with the ground strap because it can get lost if the terminals are loose. If it does get lost - you can use a short bare wire.

There are two good reasons for using these ground terminals. The first is finding and fixing hum and the second is preventing hum. If you have plugged everything in right and you are getting hum then you have a number of options with these terminals. You can try simply moving the strap
so that chassis ground is separate from circuit ground. This is similar to breaking off the third pin AC ground but includes the ground from rack mounting . One can experiment with attaching a wire between the console ground and the circuit ground or between a rack and the chassis ground. These are all techniques some technicians use when wiring studios. They also often cut the ground (shield) on one side of the cable to prevent loops. DO NOT cut the shield on MIC cables because you lose phantom, shielding at the mic, and hum only gets worse ! One other cause of hum - Some gear may radiate a field into whatever is closest. Move the Mic Pre or the offender away from each other. That may help.
 
That aside and assuming there are no actual faults causing the problem, rather just a typical ground loop

Don't get me wrong, I think it probably IS a ground issue but *assuming* is different to *knowing*.

Nothing will burn up and no one will die if initially the building wiring is checked and the equipment is checked for fault

I think that was the point I was trying to make... I think we must essentially be on the same page, just looking from slightly different angles :)

But keep your saftey hat on...nothing wrong with that.
Thanks! I'm relieved you're not offended or think i'm having a go at you, not at all my aim :D

...erm so yes ... be careful kiddakota ;)
 
We ARE on the same page...just splitting the hair from opposite ends. :)

From my own experiences trying to "exorcise" hum issues, I know that audio ground loops are not generally caused by bad/unsafe electric conditions or gear...rather just a conflict of audio/circuit ground VS chassis ground VS mains ground....as I'm sure you will agree.

I was only cutting to the chase and suggesting he simply try a ground wire so he can get on with it...though a thorough check of his house wiring and mic PS is certainly the 1st step and can be done easily with a DVM.

Heck...if you ever find serious voltage coming off the mic's PS chassis....STOP!!!! :eek: :D
 
Agreed! A DI box with an earth lift switch does wonders 95% of the time if it's in the signal chain.
The fact that he gets it on one mic and not another is interesting though, assuming he has literally swapped the mic over using the same cables and phantom power source, channel strip etc.
 
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