[ddots-l] Re: Ground Lift
- From: Bryan Smart <bryansmart@xxxxxxxxxxxxxx>
- To: "ddots-l@xxxxxxxxxxxxx" <ddots-l@xxxxxxxxxxxxx>
- Date: Sat, 22 May 2010 16:05:27 -0400
All very good advice.
-----Original Message-----
From: ddots-l-bounce@xxxxxxxxxxxxx [mailto:ddots-l-bounce@xxxxxxxxxxxxx] On
Behalf Of Dave Carlson
Sent: Saturday, May 22, 2010 1:41 PM
To: ddots-l@xxxxxxxxxxxxx
Subject: [ddots-l] Re: Ground Lift
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 <mailto:foristnights@xxxxxxxxxxx>
To: ddots-l@xxxxxxxxxxxxx
Cc: 'NFBnet Music Talk Mailing List' <mailto:musictlk@xxxxxxxxxx>
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?
PLEASE READ THIS FOOTER AT LEAST ONCE!
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