twotoedsloth
Joined: 26/01/08
Posts: 460
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What to do in an emergency?
#998222 - 16/07/12 08:21 PM
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Greetings,
I was recording a chamber choir in an older church yesterday. When
I got all my gear up and working there was a terrible buzz. My solution was the easiest
possible, I just plugged into a different electrical outlet, problem solved. The question
is, what are the "best practice" steps to try when one encounters what I think was ground
hum?
Thanks,
Peter
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ken long
Joined: 21/01/08
Posts: 4277
Loc: The Orient, East London
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Re: What to do in an emergency?
[Re: twotoedsloth]
#998223 - 16/07/12 08:23 PM
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batteries or battery pack back up. always.
--------------------
I'm All Ears.
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Hugh Robjohns
SOS Technical Editor
Joined: 25/07/03
Posts: 18394
Loc: Worcestershire
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Re: What to do in an emergency?
[Re: twotoedsloth]
#998236 - 16/07/12 09:42 PM
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Not clear on your powering arrangements. If all your gear was from a single mains socket,
it can't have been a ground loop. More likely to be a missing ground at the socket. If it
was a ground loop it wouldn't have gone just be changing socket.
On the other
hand, if your gear was powered from wall multiple sockets, then a ground loop was
possible, and replugging to adjacent sockets would probably cure the loop.
My
recommendation is always to test mains sockets before use with a simple plug-in mains
tester. And always power all your recording gear from a single outlet via decent plug
boards.
Hugh
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Technical Editor, Sound On Sound
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shufflebeat
Joined: 09/12/07
Posts: 2272
Loc: Manchester, UK
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Re: What to do in an emergency?
[Re: twotoedsloth]
#998240 - 16/07/12 09:54 PM
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Sound logic.
To paraphrase:
An ounce of prevention is worth a pound of
death by electrocution. As my Granny might have said.
I was mightily impressed
by a recent thread which included a link to a Farnell super duper mains tester which went
straight to the top of my Lottery List. I can't lay a click on it just now unfortunately.
--------------------
Ohm's Law states, "Your PA isn't as powerful as you think it is".
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twotoedsloth
Joined: 26/01/08
Posts: 460
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Re: What to do in an emergency?
[Re: twotoedsloth]
#998582 - 18/07/12 04:50 PM
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Thanks for your responses.
Battery backup wouldn't have helped me, as it was
an 8 hour recording session. In addition to my notebook computer, I was running a MOTU
Traveler, DAV, Audient and Benchmark mic preamps, a Tascam HDP2 backup recorder and a
headphone amp.
I was plugged into just one socket, so I guess it wasn't a
ground related hum.
The point of the message was what to do if you're in a
jam like this? I was very lucky that I solved my problem so easily. Would it have helped
if I disconnected the external mic preamps and used the four mic preamps on the Traveler
(that would mean I'd have to get rid of my spot mics, but that's not the end of the world
for a choral recording)?
Or how about flipping the power supplies over? All
of my devices are powered by 2 pin power supplies.
WAIT: The DAV has a three
pin power connector. Could this be the reason for the hum?
Thanks,
Peter
Edited by twotoedsloth (18/07/12 04:52 PM)
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Hugh Robjohns
SOS Technical Editor
Joined: 25/07/03
Posts: 18394
Loc: Worcestershire
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Re: What to do in an emergency?
[Re: twotoedsloth]
#998584 - 18/07/12 05:08 PM
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Quote twotoedsloth:
I was plugged
into just one socket, so I guess it wasn't a ground related hum.
It could have been a ground hum issue if
some earthed part of the system came into contact with another earthed part of the
building somewhere (eg a mic cable XLR connector touching a radiator panel etc).
However...
[quotee]I was very lucky that I solved my problem so
easily.[/quotete]
yes, apparently by plugging everything into a different mains
wall outlet -- which implies very strongly that it wasn't an inadvertant ground loop, but
a missing or high-impedance ground in the first wall socket.
Quote:
Would it have helped if
I disconnected the external mic preamps and used the four mic preamps on the Traveler
(that would mean I'd have to get rid of my spot mics, but that's not the end of the world
for a choral recording)?
Nope. It was probably a dodgy wall socket! The solution is to aalways test the wall
sockets before you use them. If I had a pound for every unsafe wall socket I've ever
tested at recording venues I have enough for cheap Chinese microphone by now! 
Quote:
Or how about flipping
the power supplies over? All of my devices are powered by 2 pin power supplies.
Er... I seriously hope not! The
Audient, the DAV and the Benchmark are all Class 1 devices and all require proper mains
safety earths!
hugh
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Technical Editor, Sound On Sound
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twotoedsloth
Joined: 26/01/08
Posts: 460
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Re: What to do in an emergency?
[Re: twotoedsloth]
#998589 - 18/07/12 06:15 PM
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Okay, I just checked my devices:
The Audient Mico has a 2 prong "line lump"
power supply
The Benchmark MicMan Jr has a 2 prong "wall wart" power
supply
The DAV BG1 has a 3 prong computer type cable, obviously an internal
power supply
The MOTU Traveler has a 2 prong "wall wart" power supply
The notebook computer (Lenovo X220) has a 2 prong "line lump" power supply
The Presonus HP4 headphone amp has a 2 prong "wall wart" power supply
Maybe the grounding requirements are different because I'm in Canada?
Edit:
I forgot the Tascam HDP2, which has a 2 prong "line lump" power supply.
Edited by twotoedsloth (18/07/12 06:17 PM)
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