[ddots-l] Re: Ground Lift
- From: "Dave Carlson" <dgcarlson@xxxxxxxxxxxxx>
- To: <ddots-l@xxxxxxxxxxxxx>
- Date: Sat, 22 May 2010 10:40:33 -0700
Annabel,
Red the following that I got from somewhere. It may help.
Dave
quote--The War on Hum
How to Maintain a Hum Free Audio System
By Tweak
The "war on hum"
is a major battle every home studio has to wage. I have been battling it since
I started recording, sometimes winning, sometimes losing. Currently, I am
winning
the war. The more gear you have, the more likely you are to encounter hum. Like
it or not, it's a war you have to fight. Fortunately, observing
a few principles can fix many situations.
This is deliberately a non technical article. You probably don't want a lecture
on the nature of ground loops and electrical systems. So I won't get too deep
into
it, but I will link you to some excellent sources of material at the end.
Basically, the hum you hear is typically a bass tone at 60Hz (or 50Hz, if you
are
across the pond), along with its harmonics at higher frequencies, which may
sound
like a buzz. Because this hum and buzz creates noise throughout the audio
spectrum,
its almost impossible to filter it out without totally wrecking the audio
signal.
Causes
can be many: ground loops, often caused by different electrical pathways to the
house ground, TV cable lines, bad or shorted audio cables, old equipment with
damaged
power supplies, equipment with poor or broken internal grounds, and cables that
travel
near magnetic fields. There are plenty of other sources of noise too--electric
motors,
radio stations, even your neighbor using power tools. In some cases, the
electricity
supplied by the power company may be erratic.
1. Make sure your audio gear and all devices that connect to audio gear are on
the
same house circuit
, observing the specified limits of the circuit. That is your audio interface,
monitors,
mixer, and gear connected to the mixer. Trouble shoot your house circuit breaker
so you know which switches go to which outlets in your house and most
importantly,
your studio. You want all the gear to use
the same path to ground.
Before you touch your home's electrical equipment,
Beware!
Messing with electricity can be dangerous, even fatal. If you don't know what
you
are doing, don't do it.
While this is not a magic formula to cure all ground loops, it can get rid of
many
preventable ones.
2. Use balanced gear with balanced TRS and XLR cables
. If you have to use unbalanced gear, keep the cables short, under 10 feet if
possible.
Long
RCA and TS (two wire) cables are highly susceptible to picking up hum. For
those
of you using
mixers
, this is really important. One poorly grounded device or poorly situated
unbalanced
cable can infect the whole mixer with hum. Those with a lot of vintage synths
(which
are nearly always unbalanced) will certainly run into this problem. I've had
real
good luck with
Behringer direct boxes
plugged into and powered by the board's mic preamps. You can input TS line
level
and output a hefty XLR balanced signal. Touch it up with the gain and you have
a
clean sounding vintage synth. You can't just use TRS cables and expect your
unbalanced
gear to be balanced. It does not work that way. You can use a
line level shifter
to do the job though.
3. Keep audio cables away from wall warts
, those power supply adapters that so many pieces of studio gear use. A cable
resting
on a wall-wart on the floor can pick up hum. Also
don't let the AC cables run parallel
to audio cables. If they cross, do it at 90 degree angles. This happens because
of magnetic fields that form around the the power cables and adapter. Electrons
don't always stay inside the cable jacket. Don't look now, but are they jumping
all over the place in that mess under your desk? Back in my 8 bus mixer days,
whenever
the hum started to rear its ugly head I would go under the desk and fix the
cable
paths. Result: Less Hum. It can help significantly.
If you do all the above and you still have hum, it could be that a particular
unit
is causing the problem. This happens a lot with
old gear
, whose power supplies may be weakened from years of use. Troubleshoot by
disconnecting
everything and plugging in items one by one until the culprit reveals itself.
Note
that for some gear, ground loops can persist even when equipment is not turned
on.
This is important to know when troubleshooting. You may have to disconnect the
power
cable from the wall as well as removing audio cables to ensure that a piece is
not
causing trouble. That piece may need separate treatment if you need to continue
using it. I've had good luck with the
Ebtech hum eliminator
and with direct boxes that have ground lifts.
Hard Questions and Answers
Q) When I pan my synth to the left, its clean. When I pan to the right I get
HUM.
What is wrong with my mixer?
A) Nearly always that is a cable problem. Swap them to see if the problem is
reversed.
If it is that confirms it is the cable or the gear connected to the mixer, not
the
mixer. You then might try connecting the gear with different cables. If the
problem
continues, it is likely that the problem is in the gear itself.
Q) Here's a really strange problem. When I raise the fader on my mixer, hum
disappears!
When I lower it, it comes back. WT heck is going on?
A) That's a tough one. You have to go into advanced troubleshooting mode. It's
quite possible that the problem is on a different channel than the one you are
boosting.
Start disconnecting audio cables on other channels. When the problem stops, you
have found the villain. Now peek under the desk to see if any cables are
touching
wall warts. Also check for an impedance mismatch where a +4 output is going
into
a -10 input.
Q) I hear "digital hash" in my audio. It's not hum, but almost sounds like
shortwave
radio interference.
A) Here's a cool experiment to make you more aware of magnetic fields. Connect
a
TS cable to the input of your mixer or audio interface. Turn up the volume.
Don't
plug in the other end, but use it as a sensor and point it towards each piece of
gear. As you get closer to the gear, within 1 inch, you will hear the digital
clock
signals bleed into your audio, especially when you get near the LCD. That's
digital
clock noise. Now look for a cable that strayed too close to one of these
electronic
fields. Many times, if the gear is balanced, using balanced cables will knock
this
right out.
Q) I put a hum eliminator on the outputs of my mixer but the hum is unchanged!
I
thought these items always worked!
A) They do work if you know their limitations. First you have to find the
device
causing the ground loop and put the hum eliminator on that device. You can't
use
it "downstream" as hum has already become part of the audio signal earlier in
the
chain. You must apply the hum eliminator to the source of the problem, before
the
ground loop becomes a hum problem.
Q) When I connect the audio outs from my TV cable box to my audio interface it
hums
so bad I can barely hear the program.
A) Common problem. The TV cable itself may use a different ground path than
your
studio equipment, especially if you have a lot of TVs in the house. For me, a
Hum
Eliminator completely fixes the problem.
Q) What types of rigs are best for avoiding issues with hum?
A) Avoid cheap unbalanced mixers. Those with large mixers and a lot of gear
know
that ground loop hygiene is crucial to keeping the board hum free. Those folks
have
to be especially vigilant to win the war. Going mixerless can help. Plugging
direct
into an audio interface gets rid of a lot of cables, and as we have seen, cables
can cause problems. Don't plug in gear that you know is problematic. Instead,
connect
it only when you want to record it, and run through helper devices like noise
gates
and the ones mentioned earlier in the article. Audio interfaces like the Tascam
FW1884 and Project Mix can help because they incorporate what would be several
separate
pieces into one box with one ground. I'd also avoid using cheap laptops for
audio.
We have had several problems documented at studio-central where ground loops
could
not be corrected. Likewise, adapting an audio chain to an unbalanced 1/8"
stereo
line input is just begging for trouble.
Q) Does one ever actually win the war? Can you truly ever totally eliminate
ground
loop hum in a home studio?
A) Technically, the answer is a matter of degree. The ground differential
potential
that creates ground loops is always present, but you can succeed in getting rid
of its artifact, the hum. The enemy is still there, waiting for you to let your
guard down. The way homes send current to ground will always have the potential
for ground loops, but with good gear and following a few simple practices, you
won't
hear it. When you turn up your monitors all the way (without playing anything
but
with all your gear connected) and all you hear is sweet white hiss, you know you
are, for now, winning the war.
You can leave feedback and discuss this topic here:
http://studio-central.com/phpbb/viewtopic.php?p=286223#286223
Links
Ground loop problems and how to get rid of them
Ground Loops, or 'Let Me Hum A Few Bars' [SMR]
Ground loop (electricity) - Wikipedia, the free encyclopedia
Everything you were Afraid to Ask about Cables
Threads
FAQ- Difference Between Balanced and Unbalanced
How to- Unbalanced => balanced wiring
Laptop Hummmmmmmmmm
Grounding & RFI Question
Why does my Guitar amp hum
Review of the EbTech Hum ...
Hum Eliminator, Unbal to Balanced Converter
Go to the
Next Class
home_studio_construction.htm unquote.
improve the sound of your studio
Studio Gear at
zZounds
Ebtech HE8 8-Channel Hum Eliminator Rack
a--3745/item--EBTHE8/sid--feed3
Do you hear hum or buzz in your audio signal? Are long, unbalanced lines across
stage
creating problems? Get the Hum Eliminator! Just plug the Hum Eliminator into the
signal lines between offending pieces of equipment and you're done. Quick and
easy!
Priced from 219.95
Ebtech HE2PKG Hum Eliminator (2-Channel)
a--3745/item--EBTHE2PKG/sid--feed3
Silence AC hum forever! Almost all AC hum (60Hz in the U.S.) is caused by
groundloops.
Rather than filtering, the Hum Eliminator prevents groundloops from forming in
the
first place. Just plug the Hum Eliminator into the signal lines between
offending
pieces of equipment and you're done. Quick and easy.
Priced from 59.95
Ebtech HUMX Voltage Hum Filter
a--3745/item--EBTHUMX/sid--feed3
The Hum X filters out unwanted voltage and current in the ground line that
cause
ground loop hum while simultaneously maintaining a solid, safe ground.
Priced from 59.95
Ebtech LLS2 Line Level Shifter (2 channel)
a--3745/item--EBTLLS2PKG/sid--feed3
The Line Level Shifter uses the physics of inductance and impedance matching to
increase
or decrease the signal voltage without the added noise of active electronics.
The
Line Level Shifter also converts back and forth between balanced and unbalanced
signals
automatically. It also contains Hum Eliminator technology to prevent groundloops
that cause AC hum.
Priced from 69.95
Ebtech HEXLR XLR Hum Eliminator (2-channel)
a--3745/item--EBTHEXLR/sid--feed3
The Ebtech HEXLR Hum Eliminator is designed to eliminate 60 cycle hum (60Hz AC
signal)
caused by Ground Loops. It is also designed to convert unbalanced lines to a
true
balanced lines (and vice versa). Why? Unbalanced lines are more susceptible to
picking
up electrical noise and RF interference.
Priced from 79.95
Ebtech LLSXLR Line Level Shifter (2-Channel)
a--3745/item--EBTLLSXLR/sid--feed3
The Ebtech Line Level Shifter is designed to increase or decrease signal voltage
(-10dBV and +4dBu) without adding noise. The Line Level Shifter also converts
back
and forth between balanced (+4dBu) and unbalanced (-10dBV) signals
automatically.
The Line Level Shifter also contains Ebtechs' Hum Eliminator technology to break
ground loops that cause AC hum.
Priced from 89.95
Ebtech Swizz Army 6 in 1 Cable Tester
a--3745/item--EBTSWIZZCT/sid--feed3
Checks XLR, 1/4 in., RCA, 1/8 in., TT, and MIDI cables for continuity and/or
intermittent
connections. Also detects opens and shorts for each pin. Other features include
test
tone generator (+4, -10, Mic), phantom power detector, grounded XLR shield
detector
and cable wiring display.
Priced from 89.95
Gear Finder
a--3745
Furman AR15 Series II 15-Amp Voltage Regulator
a--3745/item--FURAR15II/sid--hum
The 15 amp AR-15 II delivers a stable 120 volts of AC power to protect equipment
from problems caused by AC line voltage irregularities such as sags, brownouts,
or
overvoltages -- all of which can cause sensitive electronic equipment to
malfunction
or sustain damage. AR-15 II accepts any input voltage from 97V to 137V and
transforms
it to a constant 120V, +/-5V. Voltages beyond that range may also be converted
to
usable levels, depending on the range variance.
Monster Cable Pro 5100 Power Conditioner
Behringer DI4000 Ultra DI Pro 4-Channel Direct Box
a--3745/item--BEHDI4000/sid--hum
MXR M135 Smart Gate Pedal
a--3745/item--MXRM135/sid--hum
If you're addicted to the indispensable juice of a high gain amp or a string of
stomp boxes, you need this pedal. Because along with your hot-wired tones,
you're
probably getting a generous helping of noise. Equipped with 3 selectable types
of
noise reduction, Hiss, Mid, and Full, the Smart Gate bites down on sizzle and
hum
but lets the smallest detail of your playing through.
Mogami Gold Studio Microphone Cable
a--3745/item--MOGGSTU/sid--hum
Virtually every major recording facility in the world is wired with Mogami
cable.
This means that just about any music you choose has been recorded using Mogami
in
the audio chain. This cable is famous for unmatched accuracy, extremely low
noise
and remarkable flexibility. Top engineers rave about its amazing clarity and
silent
background. If accuracy in reproduction is your goal, this is the cable for you.
CBI BLUA Ultimate Series 1/4 in. TRS-TRS Cable
a--3745/item--CBIBLUA/sid--hum
Belden/CBI MLU "Ultimate" 20-gauge cable with braided shield. Neutrik Nickel
1/4
in. connectors; TRS - TRS male.
Neutrik NYSSPPL 48-Point TRS Balanced Patchbay
a--3745/item--NTKNYSSPPL/sid--hum
New, economic, and versatile describes the 1/4 in. modular Patch Panel. 48
balanced
channels in one rack space and just 1U high.
CBI 8-Channel TRS to TRS Snake
a--3745/item--CBIMT8/sid--hum
CBI cables give you quality connections without hissing or cut-outs. Without the
high price of other big named cable brands, CBI cables will provide you with
clean,
crisp sound. And with a variety of colors and connections, you can pick up the
perfect
cable for your individual needs and looks.
Ebtech HUMX Voltage Hum Filter
a--3745/item--EBTHUMX/sid--hum
Behringer HD400 2-Channel Hum Destroyer
a--3745/item--BEHHD400/sid--hum
Ebtech HE2PKG Hum Eliminator (2-Channel)
----- Original Message -----
From: Annabelle Susan Morison
To: ddots-l@xxxxxxxxxxxxx
Cc: 'NFBnet Music Talk Mailing List'
Sent: Saturday, May 22, 2010 09:17
Subject: [ddots-l] Ground Lift
Hi, it's Annabelle.
I tried flipping the switch for the ground lift on my EQ Machine, but it
didn't work. The 60 Cycle hum is still there. What do I do next?
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