Crazy buzz in radio studio

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samgraysound

Well-known member
Joined
Jun 9, 2014
Messages
284
Location
Olympia, WA
Hi all,

I've been asked to figure out a buzz issue at a local radio station.  I went down there to see what's up on Monday and I'm going back next week to start working on it. I have some ideas but I wanted to see what I might not be thinking of or things to try.

Here's the issue:

Whenever a mic is plugged in there is crazy buzz on that channel. 
This is true for any of the 4 input channels
No buzz when mic is unplugged.
The volume and quality of the buzz changes as the mic is moved around and rotated

The signal flow is Mic --> preamp/processor --> console.
The power routing is wall --> hum-x --> UPC --> Power conditioner
There is two different computers also on the same circuit
cabling was redone recently but I haven't looked closely at it yet.
Everything is wired through wiring blocks secured to the bottom of the desk. the console inputs are all on snaking that goes from the wiring blocks to 12-pin connectors inside the console.
All the mics are on adjustable arms secured to the desk, the mixer is bolted to the desk, the computers and rack gear are on a rack bolted to the desk.

Here's ideas I have to try:

1. Check for mechanical noise by removing mics from mounting arms
2. Make a ground lift cable and try lifting ground on each side for each leg of the signal path
3. Try an 1:1 isolation transformer at each leg of the signal path
4. Put the audio gear on a different power circuit then the computers.
5. Take the audio gear off the upc.
6. check the system ground for the mixer, make sure it is tied to electrical ground, and that all the rack gear is tied to the system ground
7. check each leg of the signal path with a portable headphone amp.

Any other ideas? Also is there a way to tell if their power has unwanted voltages or interference riding on it? Can I look at it with an oscilloscope and see?

 
Check and see that your Mechanical and Audio grounds are still sound. It sounds to me like some kind grounding issue.

Have you tried hooking up dynamic mics vs condenser mics and turned the phantom off?

Has their been any work in the building done even on other floors, like demolition or new phone or computer systems. Has the lighting been changed or serviced?

It has always amazed me how construction in commercial buildings, even on other floors can cause mayhem to audio systems.
 
Make sure all your audio equipment is connected to the same earth/Ground, I suspect your mic preamp might be on a separate ground to the console, try lifting the electrical ground on the preamp, does the noise go away? Often these problems occur because there are too many grounds, i.e every audio cable could be grounded at each end of each cable via the equipment it is connected to, effectively causing ground loops. With line level balanced analog audio, typically we have grounded the audio cable at one end only and left the ground isolated at the other end to reduce possible earth loops.
 
samgraysound said:
Whenever a mic is plugged in there is crazy buzz on that channel. 
This is true for any of the 4 input channels
No buzz when mic is unplugged.
The volume and quality of the buzz changes as the mic is moved around and rotated

I have heard this with guitars and amps. Try turning off the lights. Try connecting a long mic cable out the door with the mic in the next room. It may be RF noise from a lighting transformer.  Also check the polarity, phase, and voltage on the A/C outlets. They should all be 120/0, I have seen 60/60 before.
 
Hi Sam
You have RF demodulation . The Mic & or the Mixer is responding to the RF in the room. Try  another type of mic  and or mixer.  Is the mic an ACTIVE type (phantom powered) if so try a passive mic.
Try putting the mic into a paint can and close the top cover and see if the "BUZZ"  is gone?
Good hunting. Duke
 
cyrano said:
I'd take that UPS out of the equation first...

For sure. I wonder if it could be putting out EM interference just being in the room too.

Pip said:
Have you tried hooking up dynamic mics vs condenser mics and turned the phantom off?

Only dynamics so far. I'll bring a condenser down next week.

Pip said:
Has their been any work in the building done even on other floors, like demolition or new phone or computer systems. Has the lighting been changed or serviced?

Almost certainly. I will try to get better answers on when this problem started or if it has always been this way. The station manager was not being super clear.

Junction said:
Make sure all your audio equipment is connected to the same earth/Ground, I suspect your mic preamp might be on a separate ground to the console, try lifting the electrical ground on the preamp, does the noise go away? Often these problems occur because there are too many grounds, i.e every audio cable could be grounded at each end of each cable via the equipment it is connected to, effectively causing ground loops. With line level balanced analog audio, typically we have grounded the audio cable at one end only and left the ground isolated at the other end to reduce possible earth loops.

This is my top suspect too. Especially with the conditioner and the upc and whatever they have between the upc and the wall. I'm going to go through with a test cable and try lifting ground on each side to see if I can isolate it.

walter said:
I have heard this with guitars and amps. Try turning off the lights. Try connecting a long mic cable out the door with the mic in the next room. It may be RF noise from a lighting transformer.  Also check the polarity, phase, and voltage on the A/C outlets. They should all be 120/0, I have seen 60/60 before.

Guitar amps are unbalanced though, my understanding is theoretically a balanced system should do a much better job of rejecting interference.

Audio1Man said:
Hi Sam
You have RF demodulation . The Mic & or the Mixer is responding to the RF in the room. Try  another type of mic  and or mixer.  Is the mic an ACTIVE type (phantom powered) if so try a passive mic.
Try putting the mic into a paint can and close the top cover and see if the "BUZZ"  is gone?
Good hunting. Duke

The mics are all RE20s (passive dynamic). I was thinking about trying to shield the mic, but I feel like balanced lines should make that unnecessary.

Thanks for the advice everyone. Let me know if you think of anything else. I'll report back next week when I start digging into it.

Sam
 
Is the UPS a true sine wave generator when mains fail. If it is APC it probably is, define power conditioner, if Furman or the like get it out of there! Get the computers and monitors off the same power as well as any lighting. Why is the HumX there, is it dealing with a known problem? Racks are bolted to table, is the table metal?

I would make sure if they are all dynamics to turn off the phantom power as it is unnecessary.

It sounds like grounding for sure but I have some questions. Is it sounding like 60 HZ or higher in frequency? Is it steady or pulsing?  When you bring up the faders on the console is it additive in nature in other words does it get louder? Is it all channels on the desk? EDIT: By this I mean other inputs like unused mic/ line inputs etc.... Even if you don't use them!

I would try different mics and cables for sure.

Yes with such a small system that probably draws nothing I see no reason that the whole thing can not be fed by one dedicated 20 amp circuit.

What is the nature of the new construction?

Reexamining your first post can you expand on "wiring blocks"? As this is potentially part of your problem if it is what I think you mean. Also what is the 12 pin connector, Elco? To quote an often used GroupDIY mantra "pictures always help"!
 
Mic - Connector - Connector - Cable - Wiring block - Cable - Connector - Console --> Mumm


Mic - Connector - Connector - Cable - Connector -Console -->  ???
 
> cabling was redone recently but I haven't looked closely at it yet.

Did it *ever* work right after this "re-do"?
 
samgraysound said:
I've been asked to figure out a buzz issue at a local radio station.
If the gear used to work fine, and suddenly it doesn't, what changed? Seemingly related or not, what changed? Don't discount anything as "Naah, couldn't be that". it might be exactly that..

Gene
 
samgraysound said:
Hi all,

I've been asked to figure out a buzz issue at a local radio station.  I went down there to see what's up on Monday and I'm going back next week to start working on it. I have some ideas but I wanted to see what I might not be thinking of or things to try.

Here's the issue:

Whenever a mic is plugged in there is crazy buzz on that channel. 
Perhaps test with a dummy mic termination (say 150 ohm R and 0.001 uF cap). 
This is true for any of the 4 input channels
No buzz when mic is unplugged.
how about mic cables?
The volume and quality of the buzz changes as the mic is moved around and rotated
Perhaps the input is being unbalanced by wiring.
The signal flow is Mic --> preamp/processor --> console.
The power routing is wall --> hum-x --> UPC --> Power conditioner
There is two different computers also on the same circuit
it can be difficult to troubleshoot causes in a complex system but sometimes it helps to temporarily reduce the complexity by turning some connected gear off.
cabling was redone recently but I haven't looked closely at it yet.
was it quiet before? If yes the wiring is primary suspect.  :mad: :mad:
Everything is wired through wiring blocks secured to the bottom of the desk. the console inputs are all on snaking that goes from the wiring blocks to 12-pin connectors inside the console.
All the mics are on adjustable arms secured to the desk, the mixer is bolted to the desk, the computers and rack gear are on a rack bolted to the desk.

Here's ideas I have to try:

1. Check for mechanical noise by removing mics from mounting arms
perhaps carry a small mixer, mic, and known good cable, to confirm that it isn't the room/environment.
2. Make a ground lift cable and try lifting ground on each side for each leg of the signal path
nah
3. Try an 1:1 isolation transformer at each leg of the signal path
last resort... expensive
4. Put the audio gear on a different power circuit then the computers.
now you are just guessing...  maybe if the hum stops when you turn them off.
5. Take the audio gear off the upc.
fair test... divide and conquer.... reduce the number of variables.
6. check the system ground for the mixer, make sure it is tied to electrical ground, and that all the rack gear is tied to the system ground
maybe  but some old gear had pin 1 problems so grounding results can be non-standard
7. check each leg of the signal path with a portable headphone amp.
it sounds like the symptoms are pretty much input related.
Any other ideas? Also is there a way to tell if their power has unwanted voltages or interference riding on it? Can I look at it with an oscilloscope and see?
If the small mixer you carried in hums too then maybe power or environment is suspect.

Maybe plug a mic, with free standing mic cable, directly into the mixer input, not through the wiring blocks...

Good luck it will probably be the last thing you try.

JR
 
Thanks everyone for continued feedback. I still haven't gotten back there. The station manager needs to secure permission from the studio owner and hasn't been able to nail him down.

Pip said:
Is the UPS a true sine wave generator when mains fail. If it is APC it probably is, define power conditioner, if Furman or the like get it out of there! Get the computers and monitors off the same power as well as any lighting. Why is the HumX there, is it dealing with a known problem? Racks are bolted to table, is the table metal?

I would make sure if they are all dynamics to turn off the phantom power as it is unnecessary.

It sounds like grounding for sure but I have some questions. Is it sounding like 60 HZ or higher in frequency? Is it steady or pulsing?  When you bring up the faders on the console is it additive in nature in other words does it get louder? Is it all channels on the desk? EDIT: By this I mean other inputs like unused mic/ line inputs etc.... Even if you don't use them!

I would try different mics and cables for sure.

Yes with such a small system that probably draws nothing I see no reason that the whole thing can not be fed by one dedicated 20 amp circuit.

What is the nature of the new construction?

Reexamining your first post can you expand on "wiring blocks"? As this is potentially part of your problem if it is what I think you mean. Also what is the 12 pin connector, Elco? To quote an often used GroupDIY mantra "pictures always help"!

I did not take a picture or write down info on the UPS. Will get that when I get back in.
It is a cheapo Furman power conditioner.
The station manager has tried a lot of different things to deal with the noise, the Hum-x is one of those things.
Table is wood.

They are all dynamics.
Will check for phantom.

It does sound like 60hz but with a lot of overtones as well.
It is steady, not pulsing.
It is entirely controlled by the console faders, with them all the way down there is no buzz.
Only on lines where a mic is plugged in.

Definitely will try bypasses as many of there cables as I'm able. All the wiring is permanently installed, but at least the preamps have xlr i/o

Don't know enough about the construction will ask.

Umm. I don't know how exactly to explain the wiring blocks. They are like the ones for phone lines sort of. Will take pictures when I next am there. Will take a picture of the connectors too.

PRR said:
> cabling was redone recently but I haven't looked closely at it yet.

Did it *ever* work right after this "re-do"?

It was problem before and after they redid the cabling.
Gene Pink said:
If the gear used to work fine, and suddenly it doesn't, what changed? Seemingly related or not, what changed? Don't discount anything as "Naah, couldn't be that". it might be exactly that..

Gene

It has never worked right. Will try not to dismiss anything.
CJ said:
is it a country music station?

does it hum at high tide or low tide?

It is a country music station. I will ask about the tides. What could the tides have to do with it?
 
> What could the tides have to do with it?

I think CJ is pulling your leg.

I'm not sure. Fer instance, three of my neighbors have arc-welders. If it is a nice morning for welding, there could be a ton of buzz on the street wires. Or: I am in Lobster country. Those guys must live/work on the tides. If it is lobster-tide, the one neighbor won't be welding; otherwise he might.

Be open to odd interactions like that.
 
PRR said:
> What could the tides have to do with it?

I think CJ is pulling your leg.

I'm not sure. Fer instance, three of my neighbors have arc-welders. If it is a nice morning for welding, there could be a ton of buzz on the street wires. Or: I am in Lobster country. Those guys must live/work on the tides. If it is lobster-tide, the one neighbor won't be welding; otherwise he might.

Be open to odd interactions like that.

Caught my interest because the station is on the docks. Literally on pylons over the water
 
samgraysound said:
It is a cheapo Furman power conditioner.

It does sound like 60hz but with a lot of overtones as well.

I believe that Furman has MOVs in it, and when those start to fail, they can conduct a little, the voltage threshold of the device dropping below the line voltage peaks. Little sharp spikes generated, that follow ground wires and/or radiate everywhere, picked up by long mic cord antennas, and most anything else. Sounds similar to BZZZZZ.

I'm not saying you should start looking there, but at some point you may want to completely remove power from the Furman, and power up the stuff directly.

Good luck,

Gene

-----------------------------------

I'm gonna name my dog "Nature", because he "abhors the vacuum"

 
Return of the thread!

They finally got me back in today.

I determined the buzz is interference in the environment. I still had plenty of it, just plugging a 58 into my portable headphone amp. We shut off all the breakers in the building and it didn't change anything.

I've concluded that it is coming from nearby. They are right next to the marine terminal and various other industrial port activities. The station manager said every once in a while in the middle of the night the buzz disappears (don't know why he didn't start with that info).

I suggested they make the room a faraday cage. Don't really see any other solutions.

Sam
 
Hi Sam
What is the freq of the BUZZ? Is it 120Hz, 240Hz or 360Hz? It could be an arcing AC power line? If it is related to the AC LINE you might call EDISON / POWER COMPANY and they will send out a hunter truck (This is what they use to find leaking insulators). Get a spectrum analyzer and look. If you budget is low get an old AM transistor plastic radio, as it has a loop stick antenna and this can be used as a direction finder and start walking around looking for increasing noise.
Good hunting,  Duke
 

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