Hum/Noise/Radio Problem, any ideas?

deckerluke · 2nd March 2008, 06:09 AM

Hey guys,
I've been struggling with an overall hum and buzz from my 3 mics for 6 or 7 months now, a problem which has essentially made most recordings made from them useless, the problem is, they're (two of them) fairly nice mics and I am at a loss with how to correct the problem. Here's what's happening/the set up:

Neumann U47 (refurbished with new tubes by BLUE)
Neumann 86i (smaller bulb kind of mic..)
BLUE mouse**makes the most noise

the two neumann's are being run through an Univeral Audio LA-610 pre-amp
(both are being run through seperate LA-610's)
the BLUE mouse mic is being run straight through the 003 pre-amp straight into Pro Tools

THE PROBLEM: (sorry for caps)
hum/buzz/Noise! There is a variety noises, some seem to be radio signal, unclear as to whether or not it actually picks up on the recording. There is an unnatural amount for each mic.. seems to sound like some sort of power issue? but--

Everything, including the PSU for the U-48 is being plugged in to a Furman, so as far as grounding issues, which I'm guessing is the case, I'm at a loss. I have tried using a small three prong ground lift adaptor for each unit, (la-610's & U-48 PSU) and still get the same hum/buzz

let me know what you think,
i can post sound clips, pictures, whatever helps
and thank you if you have any ideas
deckerluke

Kiwiburger · 2nd March 2008, 08:19 AM

It could be one of a million things, so you have to start diagnosing.

Build a dummy load XLR by soldering a 100 - 200 ohm resistor between pins 2 & 3 of an XLR plug. Replace you mic with this load. Does the buzz go away? Then the mic is picking up EMI. You are fairly screwed - can you move?

If the buzz remains, it could be the cable. Replace the cable with your dummy load. If it goes away, you should investigate better cables with good shielding. Gotham GAC-3 makes a difference for me.

If the buzz is still there, it's not you mic or cables, so you have a power or grounding issue. Get some decent earth spikes fitted, where you can water them and get them moist. You might want to put in star-grounding.

A useful tool for diagnosing - or even as a solution - is an Ebtech hum eliminator. This is transformer isolation - they have models for balanced, unbalanced, -10, +4 etc. A transformer stops ground loops from occuring in the audio cables between components that have a common power ground. Transformer isolation kills these kinds of hum - at a small loss to your signal. Radial make one with Jensen transformers if you have to use one on your main signal. I got an Ebtech for my monitoring mixer which is in another room and prone to ground loop hum.

There are several other possible causes - you just have to eliminate what is causing it.

If you are in the path of bad EMI or RFI, it's a real bummer. It may be out of your control, and the easiest solution might be to move. A faraday cage is an expensive solution - I would love one for single coil guitars.

Otherwise - some mics are more resistant than others. Also, there are special customising and grounding tricks to make mics better. Stuffed if I know why mic makers don't do it right in the first place - it's like bloody guitars and amps - the market seems to accept cheap shonky practices.

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2nd March 2008, 06:09 AM	#1
deckerluke Gear maniac Join Date: Sep 2007 Posts: 216	Hum/Noise/Radio Problem, any ideas? Hey guys, I've been struggling with an overall hum and buzz from my 3 mics for 6 or 7 months now, a problem which has essentially made most recordings made from them useless, the problem is, they're (two of them) fairly nice mics and I am at a loss with how to correct the problem. Here's what's happening/the set up: Neumann U47 (refurbished with new tubes by BLUE) Neumann 86i (smaller bulb kind of mic..) BLUE mouse**makes the most noise the two neumann's are being run through an Univeral Audio LA-610 pre-amp (both are being run through seperate LA-610's) the BLUE mouse mic is being run straight through the 003 pre-amp straight into Pro Tools THE PROBLEM: (sorry for caps) hum/buzz/Noise! There is a variety noises, some seem to be radio signal, unclear as to whether or not it actually picks up on the recording. There is an unnatural amount for each mic.. seems to sound like some sort of power issue? but-- Everything, including the PSU for the U-48 is being plugged in to a Furman, so as far as grounding issues, which I'm guessing is the case, I'm at a loss. I have tried using a small three prong ground lift adaptor for each unit, (la-610's & U-48 PSU) and still get the same hum/buzz let me know what you think, i can post sound clips, pictures, whatever helps and thank you if you have any ideas deckerluke

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2nd March 2008, 08:19 AM	#2
Kiwiburger Lives for gear Join Date: Feb 2006 Posts: 3,825	It could be one of a million things, so you have to start diagnosing. Build a dummy load XLR by soldering a 100 - 200 ohm resistor between pins 2 & 3 of an XLR plug. Replace you mic with this load. Does the buzz go away? Then the mic is picking up EMI. You are fairly screwed - can you move? If the buzz remains, it could be the cable. Replace the cable with your dummy load. If it goes away, you should investigate better cables with good shielding. Gotham GAC-3 makes a difference for me. If the buzz is still there, it's not you mic or cables, so you have a power or grounding issue. Get some decent earth spikes fitted, where you can water them and get them moist. You might want to put in star-grounding. A useful tool for diagnosing - or even as a solution - is an Ebtech hum eliminator. This is transformer isolation - they have models for balanced, unbalanced, -10, +4 etc. A transformer stops ground loops from occuring in the audio cables between components that have a common power ground. Transformer isolation kills these kinds of hum - at a small loss to your signal. Radial make one with Jensen transformers if you have to use one on your main signal. I got an Ebtech for my monitoring mixer which is in another room and prone to ground loop hum. There are several other possible causes - you just have to eliminate what is causing it. If you are in the path of bad EMI or RFI, it's a real bummer. It may be out of your control, and the easiest solution might be to move. A faraday cage is an expensive solution - I would love one for single coil guitars. Otherwise - some mics are more resistant than others. Also, there are special customising and grounding tricks to make mics better. Stuffed if I know why mic makers don't do it right in the first place - it's like bloody guitars and amps - the market seems to accept cheap shonky practices.