Re: [LAU] Ground lifts, TRS, etc. to PA? USB/other signal crossover to audio?

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To: Ralf Mardorf <ralf.mardorf@...>, linux-audio-user@lists.linuxaudio.org <linux-audio-user@...>
Date: Friday, May 9, 2014 - 11:21 am

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However=2C if a ground lift is

Ground Lift is very often (read pretty much always) needed in PA systems! H=
ence why it is provided on every PA amplifier you can buy! BUT removing the=
ground from the mains input is not Ground Lift! As mentioned by others thi=
s is dangerous practice and should always be avoided as much as possible!! =
By that I mean you are welcome to risk your life in your own home if you re=
ally feel the need but it is never acceptable in any professional environme=
nt!

EG from the well-known amplifier manufacturer=2C Crown:
" The mixer=2C which drives the power amplifier=2C also receives its ground=
=0A=
from the AC power cord. When the audio cable connects the mixer to the =0A=
power amplifier the amplifier now sees a second ground from the mixer. =0A=
If the mixer and power amplifier are both plugged into the same AC power=0A=
strip then the mixer/amplifier interconnect cable shield=0A=
=0A=
can be cut to eliminate this problem. On most Crown amplifiers the=
re is a "ground lift=0A=
=0A=
" switch on the back of the amplifier that performs this function a=
nd can be used to eliminate hum caused by ground loops"
http://crownaudio.com/kb/entry/19/

As you see the Ground-Lift switch doesn't lift the ground from the input an=
d that term should not be used it this is what you are doing.

-

Now what has confused me is laptops where I get a ground hum. IE 50/60Hz (p=
lus possibly harmonics) hum even when using nothing but headphone plugged i=
nto onboard audio output=2C which is eliminated (or vastly reduced) by runn=
ing off batteries or by using a PSU with no earth pin. Never quite understo=
od why that happens when there is no connected piece of equipment for the s=
ignal to loop around... But that's not really part of this discussion =3B-)

Dale
=

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However=2C if a ground lift is&gt=3B needed=2C something is fishy and using a ground lift potentia=
lly is&gt=3B dangerous to life. _But_ even professional gear sometimes =
provides a&gt=3B ground lift.&gt=3B &gt=3B &gt=3B _________=
______________________________________&gt=3B Linux-audio-user mailing l=
ist&gt=3B Linux-audio-user@lists.linuxaudio.org&gt=3B http://lists.=
linuxaudio.org/listinfo/linux-audio-userGround Lift is very often (=
read pretty much always) needed in PA systems! Hence why it is provided on =
every PA amplifier you can buy! BUT removing the ground from the mains inpu=
t is not Ground Lift! As mentioned by others this is dangerous practice and=
should always be avoided as much as possible!! By that I mean you are welc=
ome to risk your life in your own home if you really feel the need but it i=
s never acceptable in any professional environment!EG from the well=
-known amplifier manufacturer=2C Crown:" The mixer=2C which drives the =
power amplifier=2C also receives its ground =0A=
from the AC power cord. When the audio cable connects the mixer to the =0A=
power amplifier the amplifier now sees a second ground from the mixer. =0A=
If the mixer and power amplifier are both plugged into the same AC power=0A=
strip then the mixer/amplifier interconnect cable shield=0A=
=0A=
can be cut to eliminate this problem. On most Crown amplifiers the=
re is a "ground lift=0A=
=0A=
" switch on the back of the amplifier that performs this function a=
nd can be used to eliminate hum caused by ground loops"http://crownaudio.com/kb/e=
ntry/19/
As you see the Ground-Lift switch doesn't lift the grou=
nd from the input and that term should not be used it this is what you are =
doing.-Now what has confused me is laptops where I get a gr=
ound hum. IE 50/60Hz (plus possibly harmonics) hum even when using nothing =
but headphone plugged into onboard audio output=2C which is eliminated (or =
vastly reduced) by running off batteries or by using a PSU with no earth pi=
n. Never quite understood why that happens when there is no connected piece=
of equipment for the signal to loop around... But that's not really part o=
f this discussion =3B-)Dale
=

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Messages in current thread:
[LAU] Ground lifts, TRS, etc. to PA? USB/other signal crosso..., Jonathan E Brickman, (Thu May 8, 7:31 pm)
Re: [LAU] Ground lifts, TRS, etc. to PA? USB/other signal cr..., Jörn Nettingsmeier, (Thu May 8, 10:44 pm)
Re: [LAU] Ground lifts, TRS, etc. to PA? USB/other signal cr..., Kaza Kore, (Fri May 9, 11:21 am)