8 May
2014
8 May
'14
9:30 p.m.
Last night I came to at least a working resolution of a really weird problem. I'm
hoping others can tell me what is really going on here, and what best to do about it. I
am not an electrical engineer or electrician or anything like that, I just learned a lot
from my dad and friends and trial and error.
This has to do with my MIDI synth, which is a headless Linux box, often used with three
Yoshimis running simultaneously. Input is just MIDI, either through USB direct from
keyboards or through USB MIDI adapters. The problem is other really odd high-pitched
non-static signals which are contaminating the audio, when plugged into any of three
different PAs.
The contamination has occurred no matter whether I use motherboard 1/8" jacks, FrontX
RCA jacks wired into the motherboard, custom-built Switchcraft 1/4" TS jacks wired
into the motherboard, a Prosonus USB, or a Behringer FCA202. It occurs to varying
degrees, not predictably, with all of them. AC power ground lifts sometimes have helped,
sometimes not, but not predictably: plugging into the same PC, one week the extra signals
will be there, the next week about 75% less, et cetera. Same with different MIDI methods.
Once I knocked out 90% plus by going from USB direct to MIDI through the Presonus, and
then two weeks after that it went up again (still using the Presonus) to about half what
it had been. I have tried AC ground lifts on amp, keyboard, and the box. Sometimes the
signal goes away when there is nothing connected via USB; sometimes not. Good AC
grounding has been explicitly made excellent and tested very thoroughly by at least two
professional musicians at one of these locations.
Perhaps the oddest thing I have noticed about the extra signal, sometimes, is when it
comes. I usually connect the synth box through a Roland volume pedal to PA. If the pedal
is entirely absent, it always comes. But if the pedals are there, about half of the time,
the extra signal comes in most when the pedal is in the lowest/zero volume position, and
least/zero when the pedal is in the highest/maximum volume position. The other half of
the time, the signal is always there and always the same volume, no matter what the
position of the pedal!
About three days ago, reviewing for the umpteenth time the whole memory-history of this
project, I remembered one thing I did a long time ago which seemed to knock out the extra
signal altogether (back then, it was a 60-cycle hum): I used a Radio Shack inline-audio
ground lift device, a 2" black barrel with two short double-RCA-male cables. I wore
out several sets of adapters on that thing which is why I abandoned it. But it had worked
more positively than anything else I tried. And I found other reports on the WWW of
similar setups not necessarily involving 60-cycle in the problem signal. So I
investigated the state of the art of inline audio ground lifts, found a whole lot more
easily findable options than there had been then (might have been ten years ago), found
that Behringer among others is making one using 1/4" TS/TRS, ordered the Behringer,
tried it last night, and voila, lovely gorgeous silence until the Great Key-Pressing!!!
So. I would like to rigorize this outfit a bit more; right now I have to play using the
box plugged via Firewire into the FCA202, thence via TS into the ground-lift, and then to
the PA via another TS. Here are a few questions.
1. I would love to be using 1/4" jacks built into the box. But clearly clear
grounding is a terrible problem. Sounds like I have to have the 1/4" jacks on a
non-metal plate; do you think?
2. What is the real advantage of TRS vs. TS? Some of the audio ground-lifts advertise
TS/TRS conversion and/or problem resolution; what is the deal??? Does TRS handle longer
runs better? Whenever I have the case plate reengineered, should I have it done with
TRS?
3. The 96 kHz audio available via Firewire is clearly helpful in the upper registers.
Fitting it along with a 1/4" double inline audio ground lift device into my box, is
somewhat less than appealing, especially because the metal cases of both the Fireware and
the ground lift devices, will be in contact with PC case metal, possibly resulting in more
contamination. What to do ???!???
Jonathan E. Brickman
Ponderworthy Music | jeb@ponderworthy.com<mailto:jeb@ponderworthy.com> |
(785)233-9977 | http://ponderworthy.com
8 May
8 May
10:48 p.m.
New subject: Ground lifts, TRS, etc. to PA? USB/other signal crossover to audio?
I'm not sure if I have understood your problem correctly. You refer
first to
really odd high-pitched non-static signals which are
contaminating
the audio
and later to
back then, it was a 60-cycle hum
My experience
is with a high-pitched signal of stable frequency
(actually mine was a hiss of 8000khz dropping to 6000khz for about
second at the end). It seemed to appear "randomly", and was very annoying.
I first checked for correlations in my apartment (does the signal appear
in sync with the engine of the fridge, and this kind of things). But the
problem turned out to be outside: the elevator! Although my apartment
has no direct contact with its cage, everytime someone would go up or
down, it would trigger that hiss. Once I found that, it became 100%
reproducible.
Searching in that direction I found that other people experienced
similar problems, especially in recent flats with recent elevators (mine
is 2 years old). The problem is linked to a kind of transformer which
softens the speed variations of the elevator. The device is known to
cause interferences and in theory it should be properly insulated... But
those who install it sometimes skip that.
Everything I tried to get rid of the hiss failed ... apart from
disconnecting my loudspeakers from the soundcard. That would work, but
it was not very practical. I suppose the metal coils in the speakers
acted like a kind of antenna for the interference.
So for a while I just notched out 8000khz and 6000khz where the hiss
occurred during recordings. As it had very narrow bandwidth, I could aim
the filter right at it and not loose much of the rest.
Then two months ago I upgraded my speakers, and no more hiss :-)
I'm not sure if I have understood your problem correctly. But if it's
high-pitched and seems to appear randomly, you could check for something
similar.
Good luck,
Victor
10:50 p.m.
New subject: Ground lifts, TRS, etc. to PA? USB/other signal crossover to audio?
On Thu, 8 May 2014 19:30:48 +0000
Jonathan E Brickman <jeb(a)ponderworthy.com> wrote:
Last night I came to at least a working resolution of
a really weird problem. I'm hoping others can tell me what is really going on here,
and what best to do about it. I am not an electrical engineer or electrician or anything
like that, I just learned a lot from my dad and friends and trial and error.
This has to do with my MIDI synth, which is a headless Linux box, often used with three
Yoshimis running simultaneously. Input is just MIDI, either through USB direct from
keyboards or through USB MIDI adapters. The problem is other really odd high-pitched
non-static signals which are contaminating the audio, when plugged into any of three
different PAs.
To me, a high pitched sound like this suggests that something (or a combination
of somethings) is marginally stable and different signal chains and earth loops
can set it off unpredictably. If there is a lot of gain in the system it can even
be something like speaker wires close to something not completely screened.
Usually, TRS is used for balanced signals but there can sometimes be benefit in
using it for unbalanced lines, in that the screening is separate from the return
path - mind you, in some cases that can actually cause RF interference problems!
All in all, I'd suggest going right back to first principles and connecting just
the absolute minimum system (even if that means listening on headphones),
ensuring you are free of the problem, then carefully adding bits. Do keep in
mind that if the problem re-appears it is not necessarily the last bit you
added that is at fault. It might just be completing a loop that triggers the
real culprit.
--
Will J Godfrey
http://www.musically.me.uk
Say you have a poem and I have a tune.
Exchange them and we can both have a poem, a tune, and a song.
11:15 p.m.
New subject: Ground lifts, TRS, etc. to PA? USB/other signal crossover to audio?
On Thu, 8 May 2014, Jonathan E Brickman wrote:
This has to do with my MIDI synth, which is a headless
Linux box, often used
with three Yoshimis running simultaneously. Input is just MIDI, either
through USB direct from keyboards or through USB MIDI adapters. The problem
is other really odd high-pitched non-static signals which are contaminating
the audio, when plugged into any of three different PAs.
The first thing to mention, is that for this discusion, a keyboard that
has USB out that looks to your computer like a midi port is not the same
as midi itself. A 5 pin MIDI out and in are electrically isolated. The
ground in the cable should only be connected at one end (output I think
but some here may know better) and the input end is optical exactly to
make sure there can be no ground problems. USB has a ground and +5 v both
of which can cause signal loops. Most keyboards I have seen are not
grounded... a lot of them being powered by "wall warts". My 80s DX7 does
have a grounded PS, so you want to check that. Also, It will matter if you
use the audio out on the keyboard or not (if you have any).
About three days ago, reviewing for the umpteenth time
the whole
memory-history of this project, I remembered one thing I did a long time ago
which seemed to knock out the extra signal altogether (back then, it was a
60-cycle hum): I used a Radio Shack inline-audio ground lift device, a 2"
black barrel with two short double-RCA-male cables. I wore out several sets
Is that what they called it? The normal way of isolating things is with an
audio transformer (passively). often call a DI (direct injection) box with
1/4 inch in and xlr ballanced out. (There are active ones out there too,
but I hate batteries so I won't mention them any more :) ) They come with
ground lift, phase change, pads, etc.
then (might have been ten years ago), found that
Behringer among others is
making one using 1/4" TS/TRS, ordered the Behringer, tried it last night,
and voila, lovely gorgeous silence until the Great Key-Pressing!!!
SOunds good.
1. I would love to be using 1/4" jacks built
into the box. But clearly
clear grounding is a terrible problem. Sounds like I have to have the 1/4"
jacks on a non-metal plate; do you think?
That would make no difference as most computer audio IF is a signal
against ground. The only way to deal with it is an audio transformer to
create an isolated signal to begin with in which case you want to go to
XLR that can plug right into a PA mic channel. The TRS jacks in the
computer are not ballanced but Stereo.... so next question:
are you using Stereo out? If so you want two audio transformers to two XLR
connectors. You can use adaptors to get two ballanced TRS lines (some PA
line inputs will deal well with these) or a different adaptor if you
really need an unballanced signal. Normally you would have a ground lift
just in case it actually made less noise without the ground lifted :) a
phase switch is probably of no use to you unless you also have your own
amp you use for monitoring.
2. What is the real advantage of TRS vs. TS? Some of
the audio
ground-lifts advertise TS/TRS conversion and/or problem resolution; what is
the deal??? Does TRS handle longer runs better? Whenever I have the case
plate reengineered, should I have it done with TRS?
Better to use the term ballanced or not. TRS doesn't, on it's own, mean
anything... it could just mean you have stereo out. What you want is
isolation... the ability to have no electrical connection from one unit to
the next. This can be done optically or inductively (I guess capacitors
can work too, but they can have other problems)
3. The 96 kHz audio available via Firewire is clearly
helpful in the upper
registers. Fitting it along with a 1/4" double inline audio ground lift
device into my box, is somewhat less than appealing, especially because the
metal cases of both the Fireware and the ground lift devices, will be in
contact with PC case metal, possibly resulting in more contamination. What
to do ???!???
Assuming you are using stereo, something like this could be mounted to
whatever ground is around
http://artproaudio.com/artcessories/di_boxes/product/dualzdirect/ or
http://artproaudio.com/artcessories/di_boxes/product/zdirect/
The output connectors are isolated from the case. Many TSR connectors made
for PCboard mounting have no connection to the case except what you
connect as the barrel is plastic. But the costly part is the transformer
in any case.
Any music store (not electronics store or stereo store, but one that sells
music instruments) will have at least one kind of DI box as they have been
a part of connecting powered outputs to PA inputs forever... they were not
new in the 70s when I first started playing.
--
Len Ovens
www.ovenwerks.net
9 May
9 May
12:44 a.m.
New subject: Ground lifts, TRS, etc. to PA? USB/other signal crossover to audio?
On 05/08/2014 09:30 PM, Jonathan E Brickman wrote:
AC power ground lifts sometimes have helped,
sometimes
There is no such thing as an AC power ground lift. The correct term, and
please don't take it personally, is _criminal_ _incompetence_.
Calling it anything else should be avoided, because that makes it sound
like something clever which the pros do. Rest assured, they don't.
You _always_ want your case grounded, unless you have double insulation,
and in that case, your power plug is two-pin only to begin with.
Any artist I catch on any stage I manage with tape across their ground
connectors can clock off early, with no show.
The only responsible and reasonable thing to do is a _signal_ ground
lift. Period.
--
Jörn Nettingsmeier
Lortzingstr. 11, 45128 Essen, Tel. +49 177 7937487
Meister für Veranstaltungstechnik (Bühne/Studio)
Tonmeister VDT
http://stackingdwarves.net
1:03 a.m.
On Friday, May 09, 2014 12:44:00 AM Jörn Nettingsmeier wrote:
On 05/08/2014 09:30 PM, Jonathan E Brickman wrote:
It sometimes makes sense to lift the AC ground if you are pulling power from
more than one source. (To prevent ground loops) As long everything is grounded
to the remaining source correctly.
AC power ground lifts sometimes have helped,
sometimes
There is no such thing as an AC power ground lift. The correct term, and
please don't take it personally, is _criminal_ _incompetence_.
6:05 a.m.
New subject: Ground lifts, TRS, etc. to PA? USB/other signal crossover to audio?
On Thu, 2014-05-08 at 18:02 -0500, Reuben Martin wrote:
On Friday, May 09, 2014 12:44:00 AM Jörn Nettingsmeier
wrote:
Potential difference by getting the power from different main jacks or
experiencing ground loops, because you don't care about a correct
grounding are no excuse to give a life-endangering "hint".
On 05/08/2014 09:30 PM, Jonathan E Brickman
wrote:
It sometimes makes sense to lift the AC ground if you are pulling power from
more than one source. (To prevent ground loops) As long everything is grounded
to the remaining source correctly. AC power ground lifts sometimes have helped,
sometimes
There is no such thing as an AC power ground lift. The correct term, and
please don't take it personally, is _criminal_ _incompetence_.
8:02 p.m.
On Friday, May 09, 2014 06:05:47 AM Ralf Mardorf wrote:
On Thu, 2014-05-08 at 18:02 -0500, Reuben Martin
wrote:
I'm not suggesting to cut the ground pin off. When you use an AC ground lift
they come with a metal ring to re-direct the ground connection so that
equipment using different power sources can share a common ground.
Like one of these:
http://www.parts-express.com/ac-3-prong-ground-lift-grounding-plug-adapter-…
On Friday, May 09, 2014 12:44:00 AM Jörn
Nettingsmeier wrote:
Potential difference by getting the power from different main jacks or
experiencing ground loops, because you don't care about a correct
grounding are no excuse to give a life-endangering "hint".
On 05/08/2014 09:30 PM, Jonathan E Brickman
wrote:
It sometimes makes sense to lift the AC ground if you are pulling power
from more than one source. (To prevent ground loops) As long everything
is grounded to the remaining source correctly. AC power ground lifts sometimes have helped,
sometimes
There is no such thing as an AC power ground lift. The correct term, and
please don't take it personally, is _criminal_ _incompetence_.
8:14 p.m.
New subject: Ground lifts, TRS, etc. to PA? USB/other signal crossover to audio?
On Fri, 09 May 2014 13:01:57 -0500
Reuben Martin <reuben.m(a)gmail.com> wrote:
On Friday, May 09, 2014 06:05:47 AM Ralf Mardorf
wrote:
Link to highly dangerous item not repeated!
How on earth is this legal? Do you *really* think most people will be savvy
enough to know that you're supposed to connect the tab to a proper earth?
Would they even know what a proper earth was?
There is absolutely no way of ensuring the earth is ever connected at all! A
properly designed 3pin connector ensures the earth is always connected first,
and disconnected last. It's the *only* safe way to work.
--
Will J Godfrey
http://www.musically.me.uk
Say you have a poem and I have a tune.
Exchange them and we can both have a poem, a tune, and a song.
On Thu, 2014-05-08 at 18:02 -0500, Reuben Martin
wrote:
I'm not suggesting to cut the ground pin off. When you use an AC ground lift
they come with a metal ring to re-direct the ground connection so that
equipment using different power sources can share a common ground.
On Friday, May 09, 2014 12:44:00 AM Jörn
Nettingsmeier wrote:
Potential difference by getting the power from different main jacks or
experiencing ground loops, because you don't care about a correct
grounding are no excuse to give a life-endangering "hint".
On 05/08/2014 09:30 PM, Jonathan E Brickman
wrote:
> AC power ground lifts sometimes have helped, sometimes
There is no such thing as an AC power ground lift. The correct term, and
please don't take it personally, is _criminal_ _incompetence_.
It sometimes makes sense to lift the AC ground if you are pulling power
from more than one source. (To prevent ground loops) As long everything
is grounded to the remaining source correctly. 
10 May
10 May
5:36 a.m.
New subject: Ground lifts, TRS, etc. to PA? USB/other signal crossover to audio?
On Fri, May 9, 2014 at 11:14 AM, Will Godfrey
<willgodfrey(a)musically.me.uk> wrote:
There is absolutely no way of ensuring the earth is ever connected at all! A
properly designed 3pin connector ensures the earth is always connected first,
and disconnected last. It's the *only* safe way to work.
Assuming, of course, that the receptacle is in fact grounded. And ...
remember what they say about "assume".
--
**** Listen to my FREE CD at http://www.mellowood.ca/music/cedars ****
Bob van der Poel ** Wynndel, British Columbia, CANADA **
EMAIL: bob(a)mellowood.ca
WWW: http://www.mellowood.ca
5:55 a.m.
New subject: Ground lifts, TRS, etc. to PA? USB/other signal crossover to audio?
On Friday 09 May 2014 23:36:22 Bob van der Poel did opine
And Gene did reply:
On Fri, May 9, 2014 at 11:14 AM, Will Godfrey
<willgodfrey(a)musically.me.uk> wrote:
Yup, those assumptions can get you killed. One of those little shirt
pocket hot wire sniffers has saved my bacon several times.
Cheers, Gene
--
"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Genes Web page <http://geneslinuxbox.net:6309/gene>
US V Castleman, SCOTUS, Mar 2014 is grounds for Impeaching SCOTUS
There is absolutely no way of ensuring the earth
is ever connected at
all! A properly designed 3pin connector ensures the earth is always
connected first, and disconnected last. It's the *only* safe way to
work.
Assuming, of course, that the receptacle is in fact grounded. And ...
remember what they say about "assume".
10:06 p.m.
On Friday, May 09, 2014 07:14:53 PM Will Godfrey wrote:
On Fri, 09 May 2014 13:01:57 -0500
Reuben Martin <reuben.m(a)gmail.com> wrote:
Perhaps I assume too much thinking the proper handling of power and wiring is
common knowledge. I deal with power issues on such a regular bases in my job,
that I sometimes forget that all too often people are messing with power who
have a very poor understanding of what they are doing.
I work in large event audio-video-lighting production, so it's very common for
me to be encounter power hazards that would probably give most people on this
list the creeps.
-Reuben
On Friday, May 09, 2014 06:05:47 AM Ralf Mardorf
wrote:
Link to
highly dangerous item not repeated!
How on earth is this legal? Do you *really* think most people will be savvy
enough to know that you're supposed to connect the tab to a proper earth?
Would they even know what a proper earth was?
There is absolutely no way of ensuring the earth is ever connected at all! A
properly designed 3pin connector ensures the earth is always connected
first, and disconnected last. It's the *only* safe way to work. On Thu, 2014-05-08 at 18:02 -0500, Reuben Martin
wrote:
I'm not suggesting to cut the ground pin off. When you use an AC ground
lift they come with a metal ring to re-direct the ground connection so
that equipment using different power sources can share a common ground. On Friday, May 09, 2014 12:44:00 AM Jörn
Nettingsmeier wrote:
> On 05/08/2014 09:30 PM, Jonathan E Brickman wrote:
> > AC power ground lifts sometimes have helped, sometimes
>
> There is no such thing as an AC power ground lift. The correct term,
> and
> please don't take it personally, is _criminal_ _incompetence_.
It sometimes makes sense to lift the AC ground if you are pulling
power
from more than one source. (To prevent ground loops) As long
everything
is grounded to the remaining source correctly.
Potential difference by getting the power from different main jacks or
experiencing ground loops, because you don't care about a correct
grounding are no excuse to give a life-endangering "hint". 
11:53 p.m.
New subject: Ground lifts, TRS, etc. to PA? USB/other signal crossover to audio?
On Sat, 10 May 2014 15:06:36 -0500 Reuben Martin <reuben.m(a)gmail.com>
wrote:
I work in large event audio-video-lighting production,
so it's very
common for me to be encounter power hazards that would probably give
most people on this list the creeps.
Its not professional encountering hazards and dealing with it
accordingly that give people on this list the creeps. Its
non-professionals (*) doing unsafe things without any knowledge and
with very real, very life-endangering consequences that gives us the
creeps!
I know that every production has certain types of cables deep down in
the cases. But I also know that breaking out these cables is only when
all else fails. And not by just any musician or roadie...
- Arnold
11 May
11 May
2:52 a.m.
New subject: Ground lifts, TRS, etc. to PA? USB/other signal crossover to audio?
The OP (and the rest of us) might find this interesting:
http://www.rane.com/note110.html (title: Sound System Interconnection)
Also, I'll add a 'me too' (because it's important) to what Jorn and
Fons have said: nobody playing on my stage gets to 'solve' a problem
by disabling AC ground.
On 10/05/2014, Arnold Krille <arnold(a)arnoldarts.de> wrote:
On Sat, 10 May 2014 15:06:36 -0500 Reuben Martin
<reuben.m(a)gmail.com>
wrote:
I work in large event audio-video-lighting
production, so it's very
common for me to be encounter power hazards that would probably give
most people on this list the creeps.
Its not professional encountering hazards and dealing with it
accordingly that give people on this list the creeps. Its
non-professionals (*) doing unsafe things without any knowledge and
with very real, very life-endangering consequences that gives us the
creeps!
I know that every production has certain types of cables deep down in
the cases. But I also know that breaking out these cables is only when
all else fails. And not by just any musician or roadie...
- Arnold
12:04 p.m.
New subject: Ground lifts, TRS, etc. to PA? USB/other signal crossover to audio?
PS: We should keep in mind that it's very important how the gear is
designed, what components are used. Some legal mains jacks don't provide
grounding.
https://en.wikipedia.org/wiki/File:Euro-Flachstecker_2.jpg
Gear signed with this logo
https://en.wikipedia.org/wiki/File:Double_insulation_symbol.svg
usually is not connected to ground. Attention, _at least it's not
allowed to connect ground to the case of a class II device_!
Metal case, build in power supply, Europlug
http://www2.yamaha.co.jp/manual/pdf/pa/english/mixers/RM602E.pdf
11:18 a.m.
New subject: Ground lifts, TRS, etc. to PA? USB/other signal crossover to audio?
On Fri, 2014-05-09 at 19:14 +0100, Will Godfrey wrote:
A properly designed 3pin connector ensures the earth
is always connected first,
and disconnected last. It's the *only* safe way to work.
Correct, and btw. the ground cable in the main sockets are always a
little bit longer. However, for e.g. the Brauner VM-1 tube microphone
it's similar done as described here:
http://sound.westhost.com/earth-f4.gif
The microphone is sold to all western nations, used by many experienced
engineers. IIRC we only used a capacitor, however, we bought a capacitor
that is intended for this usage. The switch to chose between a direct
connection and the connection by capacitor was labeled "ground lift".
You might call it hard-grounded and soft-grounded, all terms are
equivocal.
9 May
9 May
11:13 a.m.
New subject: Ground lifts, TRS, etc. to PA? USB/other signal crossover to audio?
On Thu, May 08, 2014 at 06:02:53PM -0500, Reuben Martin wrote:
It sometimes makes sense to lift the AC ground if you
are pulling power from
more than one source. (To prevent ground loops) As long everything is grounded
to the remaining source correctly.
If you lift the AC ground on some equipment it simply isn't
'correctly grounded' anymore.
To be properly grounded, the connection to ground must have
sufficiently low resistance, and be permanent in the sense
that it can't be removed without removing power at the same
time. Signal cables fail on both grounds (pun not intended).
--
FA
A world of exhaustive, reliable metadata would be an utopia.
It's also a pipe-dream, founded on self-delusion, nerd hubris
and hysterically inflated market opportunities. (Cory Doctorow)
11:54 a.m.
New subject: Ground lifts, TRS, etc. to PA? USB/other signal crossover to audio?
On Fri, 2014-05-09 at 09:13 +0000, Fons Adriaensen wrote:
To be properly grounded, the connection to ground must
have
sufficiently low resistance
To get rid of ground loops protective grounding can be done through a
capacitor.
Unfortunately I only found a German link:
"Tontechnische Geräte verfügen gelegentlich über einen sogenannten
Groundlift-Schalter. Mit diesem kann die Verbindung zwischen dem
Schutzleiteranschluss des Gerätes und der Signalmasse im Gerät
aufgetrennt werden. Dadurch kann eine möglicherweise existierende
Brummschleife aufgetrennt werden, wenngleich dadurch Nachteile für die
Unempfindlichkeit gegenüber Funkeinstrahlungen und anderen kapazitiven
Störeinflüssen entstehen können. Eine gute Lösung kann ein Kondensator
(etwa 0,1 µF) zwischen Signalmasse eines Gerätes und dessen
Schutzleiter/Gehäuse sein: der Kondensator bildet gegenüber dem
Brummstrom einen hohen Widerstand, gewährleistet jedoch weiterhin die
Abschirmwirkung des Gehäuses gegenüber höherfrequenten Störungen.
Voraussetzung für diese beiden Maßnahmen (Groundlift-Schalter oder
Kondensator) ist eine sogenannte sichere Trennung zwischen
netzspannungsführenden Teilen einerseits und Audiosignale als
Niederspannung übertragenden Teilen andererseits: Die Geräte müssen die
Anforderungen an eine Schutzkleinspannung (PELV – Protective Extra Low
Voltage) erfüllen.
Die Trennung der Masseverbindungen darf jedoch nicht durch das
Unterbrechen der Schutzkontakte des Netzanschlusses der Geräte erfolgen:
Hierbei wird die Schutzfunktion (Schutzerdung) aufgehoben, was im
Fehlerfall zu lebensgefährlichen Spannungen an den Gerätegehäusen führen
kann." - https://de.wikipedia.org/wiki/Erdschleife
noon
New subject: Ground lifts, TRS, etc. to PA? USB/other signal crossover to audio?
On Fri, 2014-05-09 at 11:54 +0200, Ralf Mardorf wrote:
On Fri, 2014-05-09 at 09:13 +0000, Fons Adriaensen
wrote:
AFAIK not only shielding is ensured, but also protective grounding.
To be properly grounded, the connection to ground
must have
sufficiently low resistance
To get rid of ground loops protective grounding can be done through a
capacitor.
Unfortunately I only found a German link:
"Tontechnische Geräte verfügen gelegentlich über einen sogenannten
Groundlift-Schalter. Mit diesem kann die Verbindung zwischen dem
Schutzleiteranschluss des Gerätes und der Signalmasse im Gerät
aufgetrennt werden. Dadurch kann eine möglicherweise existierende
Brummschleife aufgetrennt werden, wenngleich dadurch Nachteile für die
Unempfindlichkeit gegenüber Funkeinstrahlungen und anderen kapazitiven
Störeinflüssen entstehen können. Eine gute Lösung kann ein Kondensator
(etwa 0,1 µF) zwischen Signalmasse eines Gerätes und dessen
Schutzleiter/Gehäuse sein: der Kondensator bildet gegenüber dem
Brummstrom einen hohen Widerstand, gewährleistet jedoch weiterhin die
Abschirmwirkung des Gehäuses gegenüber höherfrequenten Störungen. Voraussetzung für diese beiden Maßnahmen
(Groundlift-Schalter oder
Kondensator) ist eine sogenannte sichere Trennung zwischen
netzspannungsführenden Teilen einerseits und Audiosignale als
Niederspannung übertragenden Teilen andererseits: Die Geräte müssen die
Anforderungen an eine Schutzkleinspannung (PELV – Protective Extra Low
Voltage) erfüllen.
Die Trennung der Masseverbindungen darf jedoch nicht durch das
Unterbrechen der Schutzkontakte des Netzanschlusses der Geräte erfolgen:
Hierbei wird die Schutzfunktion (Schutzerdung) aufgehoben, was im
Fehlerfall zu lebensgefährlichen Spannungen an den Gerätegehäusen führen
kann." - https://de.wikipedia.org/wiki/Erdschleife
1:17 p.m.
New subject: Ground lifts, TRS, etc. to PA? USB/other signal crossover to audio?
On Fri, May 09, 2014 at 11:54:23AM +0200, Ralf Mardorf wrote:
On Fri, 2014-05-09 at 09:13 +0000, Fons Adriaensen
wrote:
Certainly not. Just read the text you posted.
It says that some equipment may allow to separate signal ground
and protective ground, and that in that case the two may remain
connected via a capacitor which may improve HF shielding.
It certainly doesn not say that you can disconnect protective
ground, on the contrary it does say that you must not do that.
--
FA
A world of exhaustive, reliable metadata would be an utopia.
It's also a pipe-dream, founded on self-delusion, nerd hubris
and hysterically inflated market opportunities. (Cory Doctorow)
To be properly grounded, the connection to ground
must have
sufficiently low resistance
To get rid of ground loops protective grounding can be done through a
capacitor.
7:25 p.m.
New subject: Ground lifts, TRS, etc. to PA? USB/other signal crossover to audio?
On Fri, 9 May 2014 11:17:00 +0000
Fons Adriaensen <fons(a)linuxaudio.org> wrote:
On Fri, May 09, 2014 at 11:54:23AM +0200, Ralf Mardorf
wrote:
Beat me to it! It's quite scary what people think is 'safe enough' :(
--
Will J Godfrey
http://www.musically.me.uk
Say you have a poem and I have a tune.
Exchange them and we can both have a poem, a tune, and a song.
On Fri, 2014-05-09 at 09:13 +0000, Fons
Adriaensen wrote:
Certainly not. Just read the text you posted.
It says that some equipment may allow to separate signal ground
and protective ground, and that in that case the two may remain
connected via a capacitor which may improve HF shielding.
It certainly doesn not say that you can disconnect protective
ground, on the contrary it does say that you must not do that. To be properly grounded, the connection to ground
must have
sufficiently low resistance
To get rid of ground loops protective grounding can be done through a
capacitor.
5:57 a.m.
New subject: Ground lifts, TRS, etc. to PA? USB/other signal crossover to audio?
On Fri, 2014-05-09 at 00:44 +0200, Jörn Nettingsmeier wrote:
There is no such thing as an AC power ground lift. The
correct term, and
please don't take it personally, is _criminal_ _incompetence_.
+1
What Jörn tries to point out isn't an insult, it's a lifesaving must.
7:03 a.m.
New subject: Ground lifts, TRS, etc. to PA? USB/other signal crossover to audio?
On Fri, 9 May 2014, Jörn Nettingsmeier wrote:
On 05/08/2014 09:30 PM, Jonathan E Brickman wrote:
+1
For the number of times I have seen it on the list it shouldn't
need repeating. Better repeated than dead though. Isolating signal lines
works fine.
--
Len Ovens
www.ovenwerks.net
AC power ground lifts sometimes have helped,
sometimes
There is no such thing as an AC power ground lift. The correct term, and
please don't take it personally, is _criminal_ _incompetence_.
8:14 a.m.
New subject: Ground lifts, TRS, etc. to PA? USB/other signal crossover to audio?
On Thu, 2014-05-08 at 21:54 -0700, Len Ovens wrote:
Better repeated than dead though.
JFTR if you know what you're doing a ground lift could be a temporarily
solution, e.g. the power supply of the Brauner VM1 tube microphone has
got a ground lift through a capacitor. However, if a ground lift is
needed, something is fishy and using a ground lift potentially is
dangerous to life. _But_ even professional gear sometimes provides a
ground lift.
1:21 p.m.
New subject: Ground lifts, TRS, etc. to PA? USB/other signal crossover to audio?
However, if a ground lift is
needed, something is fishy and using a ground lift
potentially is
dangerous to life. _But_ even professional gear sometimes provides a
ground lift.
_______________________________________________
Linux-audio-user mailing list
Linux-audio-user(a)lists.linuxaudio.org
http://lists.linuxaudio.org/listinfo/linux-audio-user
Ground 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 input
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 welcome to risk your life in your own
home if you really feel the need but it is never acceptable in any professional
environment!
EG from the well-known amplifier manufacturer, Crown:
" The mixer, which drives the power amplifier, also receives its ground
from the AC power cord. When the audio cable connects the mixer to the
power amplifier the amplifier now sees a second ground from the mixer.
If the mixer and power amplifier are both plugged into the same AC power
strip then the mixer/amplifier interconnect cable shield
can be cut to eliminate this problem. On most Crown amplifiers there is a
"ground lift
" switch on the back of the amplifier that performs this function and 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 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 ground hum. IE 50/60Hz (plus possibly
harmonics) hum even when using nothing but headphone plugged into onboard audio output,
which is eliminated (or vastly reduced) by running off batteries or by using a PSU with no
earth pin. 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 of this
discussion ;-)
Dale
1:29 p.m.
New subject: Ground lifts, TRS, etc. to PA? USB/other signal crossover to audio?
On Fri, May 09, 2014 at 11:21:32AM +0000, Kaza Kore wrote:
Now what has confused me is laptops where I get a
ground hum. IE 50/60Hz (plus possibly harmonics) hum even when using nothing but headphone
plugged into onboard audio output, which is eliminated (or vastly reduced) by running off
batteries or by using a PSU with no earth pin. 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 of this discussion ;-)
That is due to crappy PCB design. The rules for audio and for digital
electronics are very different, and most PCB designers haven't got a
clue about how ground tracks and planes for audio and just apply the
guidelines for digital boards.
Ciao,
--
FA
A world of exhaustive, reliable metadata would be an utopia.
It's also a pipe-dream, founded on self-delusion, nerd hubris
and hysterically inflated market opportunities. (Cory Doctorow)
2:17 p.m.
New subject: Ground lifts, TRS, etc. to PA? USB/other signal crossover to audio?
Fons, Dale, I didn't verbalised well. I wanted to point out that
completely interrupting the mains ground is extremely dangerous (I guess
I verbalised this part very well), but that not everything in a device
needs to be directly connected to ground (regarding to this I inartfully
expressed), connections to ground sometimes are done by resistors or
capacitors.
10 May
10 May
3:51 a.m.
On May 9, 2014 12:44:00 AM Jörn Nettingsmeier wrote:
On 05/08/2014 09:30 PM, Jonathan E Brickman wrote:
Although it might not relate directly to the OP's question,
since the safety topic came up I would like to relate a story about
one reason you should never remove power ground pins and make
sure your outlets are grounded:
Some relevant info:
http://en.wikipedia.org/wiki/Cheater_plug
Grounding is important not only for day-to-day usage, but in case of
unexpected catastrophic failure.
So this high-power powered PA speaker decides to SMOKE in the
middle of a practice.
Diagnosis, and a theory of what caused it:
A component on the Switch Mode Power Supply board's +15V rail short-circuited.
The short still exists, haven't tried to find the component yet,
because:
It appears that, at the exact moment of the short, the SPMS wanted to dump
a lot of current into the chassis ground while things went haywire
for a moment and the driver was still running and things shut down
and caps discharged and so on.
But here, the Input Board, which is fed by the +/- 15V power rails,
was DESTROYED. The tops of all ten or so 8-pin op-amp ICs were
completely BURNT and CHARRED open.
More tellingly, in this model there's a 10-ohm surface-mount ground RESISTOR
on the Input Board, connecting INPUT signal ground to CHASSIS ground.
The resistor, and the circuit board area, were completely BURNT and CHARRED.
(A mixer was connected to this PA, on the same AC circuit)
Conclusion:
I could only conclude there was no CHASSIS (AC) ground, or it was breached
by a bad or loose cord.
If AC ground had been intact, the catastrophic current would have been dumped
into the AC ground and there would have been little or NO potential difference
across the 10-ohm ground resistor to cause THAT amount of damage to it.
The resulting wackiness in voltage swings could be what destroyed all those
Input Board op-amp ICs.
So the current wanted to flow into the AC ground but instead took the
easiest path it could - through the surface-mount 10-ohm ground resistor,
back through the INPUT cable and into the MIXER ground.
(I checked: The mixer has no such resistor. Signal ground = chassis ground.
The mixer still works. Still, I advised the owner to change his input cable.)
Tim.
AC power ground lifts sometimes have helped,
sometimes
There is no such thing as an AC power ground lift. The correct term, and
please don't take it personally, is _criminal_ _incompetence_.
Calling it anything else should be avoided, because that makes it sound
like something clever which the pros do. Rest assured, they don't.
You _always_ want your case grounded, unless you have double insulation,
and in that case, your power plug is two-pin only to begin with.
Any artist I catch on any stage I manage with tape across their ground
connectors can clock off early, with no show.
The only responsible and reasonable thing to do is a _signal_ ground
lift. Period.
11:08 a.m.
New subject: Ground lifts, TRS, etc. to PA? USB/other signal crossover to audio?
On Fri, May 09, 2014 at 09:50:49PM -0400, Tim E. Real wrote:
Conclusion:
I could only conclude there was no CHASSIS (AC) ground, or it was breached
by a bad or loose cord.
A very typical story, and you have been lucky.
Proper grounding should never be taken for granted. A few years
ago I inspected a set of 8 newly delivered active speakers -
quite expensive ones from a very reputable brand. Three of
them were not properly grounded. There was a short wire from
the ground pin of the power socket to one of the screws used
to fix the main PCB to the chassis. And those screws were black
anodised... The scary part was that ground continuity had not
even been tested at the factory.
Regarding those 'cheat plugs', if I find any of those or any
other tricks to defeat proper grounding on my watch, I take
the same attitude as Joern - either those things get fixed
*immediatetly* or the user can pack his bags.
Ciao,
--
FA
A world of exhaustive, reliable metadata would be an utopia.
It's also a pipe-dream, founded on self-delusion, nerd hubris
and hysterically inflated market opportunities. (Cory Doctorow)
9 May
9 May
5:40 a.m.
New subject: Ground lifts, TRS, etc. to PA? USB/other signal crossover to audio?
It's impossible that a ground lift has got any effect when using MIDI
connections, since MIDI
1. only one sided is connected to ground, the other end is undone
2. is optical decoupled
If a ground lift has got any positive effect, something likely seriously
is broken in a life-endangering way.
5:54 a.m.
New subject: Ground lifts, TRS, etc. to PA? USB/other signal crossover to audio?
Rereading your mail, I guess I misunderstood your request.
One tip and one ring allows unbalanced mono connections only, while one
tip and two rings allow balanced mono or unbalanced stereo connections.
Anyway, using a ground-lift to solve a noise issue is dangerous. We all
experienced this issue. I add a switch to one of my 19" effects, but we
shouldn't do this. If you're using a ground-lift, at least take care
that it's not simply completely disconnecting from ground, it's better
when there still is a connection to ground by a capacitor.
3802
days inactive
3805
days old
linux-audio-user@lists.linuxaudio.org
30 comments
14 participants
participants (14)
-
Arnold Krille -
Bob van der Poel -
Fons Adriaensen -
Gene Heskett -
Jonathan E Brickman -
Jörn Nettingsmeier -
Kaza Kore -
Len Ovens -
mark hadman -
Ralf Mardorf -
Reuben Martin -
Tim E. Real -
Victor -
Will Godfrey