More hum/buzz/60hz noise.

Steenamaroo

Steenamaroo

...
Hey all.

Did some recording in my garage setup the other day but was plagued by background hum that sounded like your mains hum.
The hum becomes more/less intense depending where i move the mic around the room, and obviously increases greatly as I move towards equipment with transformers etc.

I tried different inputs, different cables, different mics etc with the same result.

Instead of ripping stuff apart I went and got my macbook and firestudio mobile from the bedroom.
There's no problem with hum on that setup in the bedroom unless i literally hold the mic a few inch from a wall wart or something. Normal i figure?

So i take that to the garage, fire it up, and boom. There's my irritating hum.

Now, this macbook/firestudio setup is completely battery powered and not integrated with any mains gear at all so that takes ground loops out of the equation.

I only get this hum using dynamic mics (tested re20,re11 and sm58). Signal is absolutely clear using a little naiant omni condenser.

Even if i move the mic (dynamic) out to the middle of the room the hum is still there. Sure it's pretty distant but it's enough to annoy you.

I went around turning stuff off, no lights, no computer monitors. Shutdown everything except for my computer.
This did change the intensity of the hum but didn't eradicate it so my question is..
Is this normal? Have I just not noticed it before?

It seems like something I would have picked up on but I can't think of anything that's changed outside in terms of gear or wiring.

Thanks all.
 
Guess your stuck recording with omni microphones from here on out Paul.


Has anything changed outside or at your neighbors house? Like a new outside light or bug zapper.
 
Lol. Oul Jon snuck round in the night and broke all my other mics! :p

I'm not aware of anything changing. I initially thought it was a grounding issue in those racked preamps; That's what it sounded like but I've ruled that out.

It's like dynamic mics are just more susceptible to stuff that they are normally a little susceptible to.

If i 'scan' around the room with a mic, near monitors, screens, preamps etc i get the buzz (as you would) but it just seems so much louder than it should be.
 
Seems somewhat odd to me, too. Obvious question, but have you tried swapping different mic cables around? For instance, if you get it where you don't have the hum on the condenser, unplug the mic, and plug in a dynamic using the same cable? Still there? Try turning the phantom on and off to see if that changes anything. That's kinda where I think you're problem might be. The main difference between the two is going to be the phantom power. Try it and see. I'd like to know the eventual outcome, as I like to try and mentally file things like this away for future reference.
Good luck.
 
Thanks for the input cardio. Unfortunately I did try all those things.
Phantom power on/off makes no difference to the hum, and I literally did what you said, switching the mic only so the cable and input were all the same.

I hate stuff like this. My only problem out here was computer fan noise. The way it is at the minute if I had the gain up enough that fan noise was an issue, the buzz would definitely be louder.
 
moresound said:
Has anything changed outside or at your neighbors house? Like a new outside light or bug zapper.
Click to expand...

+1 on this. What time of day? Is there e.g. a mercury lamp nearby? How close to power lines? You mentioned lights, etc, is there a subpanel in the garage? Have you tried, e.g. cutting all the mains power to the garage/garage subpanel. (I'm reaching here but...) What about a cell phone?

Have you tried wiring an XLR jack w/ a tiny capacitor to reduce RFI?

http://www.bartlettmics.com/newsletter/newsletter 10-09.pdf
 
Actually, great call. I'll bring the lappy back out and hit the trip for the garage. See how it fares with no mains power getting out here.

Even if that solves the problem I don't know why it's stated now, but we'll cross that bridge when we get there right?

Thanks.
 
Dynamic mics are normally extremely resistant to this sort of thing (well quality ones anyway) because they use shielded, humbucking coils. However, they don't all use mumetal shielded transformers, so in a strong enough field just about any mic transformer can pick up hum. That's a pretty strong field though, you'd have to be close to a power transformer in another bit of kit.

The second likely cause is if the interface has poor common mode rejection, if it is poorly shielded, or has poor ground design. This may be why I did better: because my output signal is hotter, it may cover up the hum that is leaking in elsewhere.

Make yourself a 150 ohm termination in an XLR connector--actually do two of them, one balanced at 150 and one unbalanced at 2k2 or higher--the unbalanced one will be a good antenna for detecting various field strengths; with the balanced 150 ohm one you should be able to suss out if you have a cable or interface problem. If you get hum with the 150 ohm termination direct into the interface, then the interface has a problem. If not direct in the interface, but with a cable, then it's probably poor CMRR, but it could be a poor cable, or improper grounding in the interface. If nothing with the 150 ohm, but with the mic, then it's the mics (it probably isn't the mics, EV knows what they are doing and the RE20 is designed as a broadcast mic where such things aren't tolerated).
 
OK, that's great stuff to go on. I'll definitely give that a go tomorrow. I'll try killing the mains too to see what happens.
Just to check, balanced would be between pins 2 and 3, but unbalanced would be between pin 2 (or 3) and 1?

Thanks everyone.
 
While driving home Sunday night I was trying to pick up the Superbowl on AM radio - Every time I went by a factory or a parking lot with a lot of street lights I would get an interference and I could tell when I passed a so called bad transformer up on the pole. What a racket!

So that's your problem right there Paul. You are the proud father of an AM radio. :p
 
Paul have you tried using a 3 foot XLR cable to connect those dynamic microphone to see if that helps with the hum?
 
moresound said:
Paul have you tried using a 3 foot XLR cable to connect those dynamic microphone to see if that helps with the hum?
Click to expand...

No, but I have plugged microphones directly into the preamp. Some of those EV mics have a slim enough base that it goes straight into the XLR socket. (Top tip for a handy talkback mic right there!)

If anything that was worse. Having the mic anywhere near the gear (computer/screens/preamps/interface) just introduces stronger buzz.
 
That's a different problem then. I don't hear mechanical noise in the room.
Kinda like when your phone noise comes through your hifi.

Are you using a motu 828? Some of them have problems with buzzing noise (audible in the room). I've read about people remounting the transformers with rubber bushes or something like that. Worth a google anyway.
 
Your gain is almost invariably higher for dynamic mics than for condensers, which could be the reason you're hearing hum only from the dynamic mics.

Try using the power supply with your laptop so that your analog ground isn't floating. See if that fixes the problem.
 
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