The Signal comes from the Source.
That Signal is a Flow from the Source and a Return to the Source.
There should be no Signal routed to another part of the amplifier.
The Flow and Return start at the Source and finish at the input devices of the receiver.
The Flow and Return wires stay close coupled throughout the whole route.
That Signal is a Flow from the Source and a Return to the Source.
There should be no Signal routed to another part of the amplifier.
The Flow and Return start at the Source and finish at the input devices of the receiver.
The Flow and Return wires stay close coupled throughout the whole route.
Absolutely NOT !
You May Call Me a Madman...
Andrew,
I'm doing it! There is a big fat 4 gauge stranded cable running from my cable box and TV back and up through my shelves of gear, that has ground leads going out to each chassis, and one to earth.
Here is what I'm doing to each input end - cutting 2 inches of jacket, cutting the copper braid, and soldering a 200 ohm resistor and a 10 pF cap in parallel.
I forgot to take a picture of wrapping the cable with electrical tape, starting at the right and stopping when just the two R and C leads are sticking out on the left. They are soldered to the braid. Then that frayed braid and jacket on the left are pulled back and the copper is sort of re-braided over the taped R and C. Then, shrink tubing that comes with hot melt glue inside is applied over the whole thing, so the cable won't pull apart if unplugged by the jacket.
After pulling the braid and jacket back towards the break, I end up with about an inch of missing cable jacket. The braid from the left telescopes over the taped cut with the R and C, so the shield is again covering everything, more or less. And voila:
200 ohms out to 200Khz depending in input impedance, very little above. No more audio ground loops, yet shielding for RFI. Now I haven't tested this yet. I might get tripped up by the inputs of my Adcom amps which are above ground. I still want to do the same thing to the outer shield of my HDMI cables without ruining them (as well).
If I'm wrong, I'll add a bypass or a switch to each end of the cables I'm making up, or cut them off and put just a plug on.
Andrew,
I'm doing it! There is a big fat 4 gauge stranded cable running from my cable box and TV back and up through my shelves of gear, that has ground leads going out to each chassis, and one to earth.
Here is what I'm doing to each input end - cutting 2 inches of jacket, cutting the copper braid, and soldering a 200 ohm resistor and a 10 pF cap in parallel.
I forgot to take a picture of wrapping the cable with electrical tape, starting at the right and stopping when just the two R and C leads are sticking out on the left. They are soldered to the braid. Then that frayed braid and jacket on the left are pulled back and the copper is sort of re-braided over the taped R and C. Then, shrink tubing that comes with hot melt glue inside is applied over the whole thing, so the cable won't pull apart if unplugged by the jacket.
After pulling the braid and jacket back towards the break, I end up with about an inch of missing cable jacket. The braid from the left telescopes over the taped cut with the R and C, so the shield is again covering everything, more or less. And voila:
200 ohms out to 200Khz depending in input impedance, very little above. No more audio ground loops, yet shielding for RFI. Now I haven't tested this yet. I might get tripped up by the inputs of my Adcom amps which are above ground. I still want to do the same thing to the outer shield of my HDMI cables without ruining them (as well).
If I'm wrong, I'll add a bypass or a switch to each end of the cables I'm making up, or cut them off and put just a plug on.
HUUUUMMMMM
All right, I finally completed all the cabling. There is one and only one direct ground path between each box. Tried it last night, and my Adcom power amps hummed like an ocean liner.
Connected jumpers from chassis to input shield and it became dead quiet. So now I must tack solder a short wire from shield to the back panel of each amp. This must be what they mean by "above ground."
All right, I finally completed all the cabling. There is one and only one direct ground path between each box. Tried it last night, and my Adcom power amps hummed like an ocean liner.
Connected jumpers from chassis to input shield and it became dead quiet. So now I must tack solder a short wire from shield to the back panel of each amp. This must be what they mean by "above ground."
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Adcom GFA-535II Hates My Grounding Scheme
After installing my custom cables there seems to be a few errors here and there so I will have to get out the signal generator and some shorted RCA plugs and start testing from the power amps backwards. The three Adcom GFA-535II's seem to really not like my isolation of shields with 200 ohm resistors. Even when I jumper the input shields to the common ground there is more hum than with no ground connection at all.
This from the owners manual:
If the GFA-53511 is to be mounted on a rack, along with other components which are interconnected to the GFA-53511, the amplifier's chassis must be insulated from the metal-rack rails to prevent ground loops, especially if the rack is grounded to "earth", and to avoid defeating the audio grounding scheme of the power amplifier (the audio-input grounds are isolated from and above the chassis ground).
My "rack," the fat ground cable, is grounded to earth. I think for these three amps, I'll just connect standard cables and not ground the chassis.
After installing my custom cables there seems to be a few errors here and there so I will have to get out the signal generator and some shorted RCA plugs and start testing from the power amps backwards. The three Adcom GFA-535II's seem to really not like my isolation of shields with 200 ohm resistors. Even when I jumper the input shields to the common ground there is more hum than with no ground connection at all.
This from the owners manual:
If the GFA-53511 is to be mounted on a rack, along with other components which are interconnected to the GFA-53511, the amplifier's chassis must be insulated from the metal-rack rails to prevent ground loops, especially if the rack is grounded to "earth", and to avoid defeating the audio grounding scheme of the power amplifier (the audio-input grounds are isolated from and above the chassis ground).
My "rack," the fat ground cable, is grounded to earth. I think for these three amps, I'll just connect standard cables and not ground the chassis.
Just jumping in for a sec in case nobody has yet pointed you to this: http://www.rane.com/pdf/ranenotes/Sound_System_Interconnection.pdf
Having to insulate chassis's from the rack and any resistors in the shields just doesn't seem to be a good idea.
Go to the troubleshooting section (about page 100) of Bill Whitlock's seminar paper:
"An Overview of Audio System"
'Grounding and Interfacing'
by
Bill Whitlock, President
Jensen Transformers, Inc.
Life Fellow, Audio Engineering Society
Life Senior Member, Institute of Electrical & Electronic Engineers
An audio system is rarely a plug-and-play affair. Noises often plague the
system even if everything is done according to conventional wisdom. Did the
electrician screw up? Is the AC power dirty? Is the equipment to blame? Are
the cables poorly shielded? This presentation will discuss the "secret" forces
that drive ground loops, how they contaminate our signals, and new tools to
make troubleshooting faster and easier. Among the topics will be equipment
design errors that can make life miserable for installers and users, how
manufacturers manipulate "specs" to deceive, how new test standards and
instruments can make manufacturers honest, why expensive cables probably
won't help, and things your electrician can do to reduce or eliminate problems.
http://centralindianaaes.files.wordpress.com/2012/09/indy-aes-2012-seminar-w-notes-v1-0.pdf
Also make a John Windt 'hummer' tester and check your system.
Go to the troubleshooting section (about page 100) of Bill Whitlock's seminar paper:
"An Overview of Audio System"
'Grounding and Interfacing'
by
Bill Whitlock, President
Jensen Transformers, Inc.
Life Fellow, Audio Engineering Society
Life Senior Member, Institute of Electrical & Electronic Engineers
An audio system is rarely a plug-and-play affair. Noises often plague the
system even if everything is done according to conventional wisdom. Did the
electrician screw up? Is the AC power dirty? Is the equipment to blame? Are
the cables poorly shielded? This presentation will discuss the "secret" forces
that drive ground loops, how they contaminate our signals, and new tools to
make troubleshooting faster and easier. Among the topics will be equipment
design errors that can make life miserable for installers and users, how
manufacturers manipulate "specs" to deceive, how new test standards and
instruments can make manufacturers honest, why expensive cables probably
won't help, and things your electrician can do to reduce or eliminate problems.
http://centralindianaaes.files.wordpress.com/2012/09/indy-aes-2012-seminar-w-notes-v1-0.pdf
Also make a John Windt 'hummer' tester and check your system.
More Strange Effects
My adcom slc505 passive preamp also shows strange effects with my new interrupted-shield cables. Terrible crosstalk. I can switch to another source and still here the other source if it is still on. I think the slc505 has an "above ground" scheme as well as their power amps but I don't have a manual. It seems that any device with above ground inputs behaves badly if a cable acts at cross purposes with that scheme. I'll try it with regular cables and check the noise each way.
A John Windt hummer tester? Hmmm. Or should I say Hummmmm?
My adcom slc505 passive preamp also shows strange effects with my new interrupted-shield cables. Terrible crosstalk. I can switch to another source and still here the other source if it is still on. I think the slc505 has an "above ground" scheme as well as their power amps but I don't have a manual. It seems that any device with above ground inputs behaves badly if a cable acts at cross purposes with that scheme. I'll try it with regular cables and check the noise each way.
A John Windt hummer tester? Hmmm. Or should I say Hummmmm?
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Okay, I've backed up and am measuring AC voltage at the speakers. So far I have just the power amplifiers connected to the speakers, and shorted RCA plugs on the inputs (plenty of those thanks to the bulk cable I chose). I will move backwards towards the sources as I test.
One speaker has a hum that does not show at the amp when an 8 ohm resistor is substituted, so I think the external crossover is sitting too near an uninterruptible power supply. I'll track down that hum next time the wife is out of the house.
Right now the noise voltage is between 0.6 and 1 mv in the working channels, with each chassis grounded/earthed. When I remove the ground connection, noise goes up about 0.1 mv, so chassis ground reduces garbage as well as increases safety.
I guess the real noise will happen when I go back and connect my switcher, which is a DACT 8-channel and many RCA jacks in an old-school metal rack box. This will be with my interrupted shield cables, 200 ohms shield impedance. The power amps will not like it.
One speaker has a hum that does not show at the amp when an 8 ohm resistor is substituted, so I think the external crossover is sitting too near an uninterruptible power supply. I'll track down that hum next time the wife is out of the house.
Right now the noise voltage is between 0.6 and 1 mv in the working channels, with each chassis grounded/earthed. When I remove the ground connection, noise goes up about 0.1 mv, so chassis ground reduces garbage as well as increases safety.
I guess the real noise will happen when I go back and connect my switcher, which is a DACT 8-channel and many RCA jacks in an old-school metal rack box. This will be with my interrupted shield cables, 200 ohms shield impedance. The power amps will not like it.
I have a problem following your description of what you are actually doing and why.
"So far I have just the power amplifiers connected to the speakers, and shorted RCA plugs on the inputs." and "I think the external crossover is sitting too near an uninterruptible power supply."
Which is it? amp only with inputs shorted or is there an external crossover with a PSU connected?
The best solutions are going to be found by fixing faults inside the components. Not by adding this or that (ground) cable, expecting the noise to disappear and at what cost to audio quality.
"So far I have just the power amplifiers connected to the speakers, and shorted RCA plugs on the inputs." and "I think the external crossover is sitting too near an uninterruptible power supply."
Which is it? amp only with inputs shorted or is there an external crossover with a PSU connected?
The best solutions are going to be found by fixing faults inside the components. Not by adding this or that (ground) cable, expecting the noise to disappear and at what cost to audio quality.
The Whitlock presentation is interesting, but I worry his agenda (sell transformers) is missing one point. The return current will take the lowest impedance path back, which may not be the shield of the cable. This can cause a lot of confusion, because it is not obvious whether you should live with this, or encourage the return current to go back the way you want it to go. Most RCAs are insulated now, so this can easily be done. But should it be done?
Ben Duncan wrote some interesting articles on mains, but then again sells products in this area and has association with Russ Andrews...
Identifying & Solving Mains Supply Problems
I have wondered about having a seperate signal ground connection in the past, but it does require being very careful to maintain safety and doesn't guarantee anything.
Galvanic isolation does seem very tempting on occasion...
Identifying & Solving Mains Supply Problems
I have wondered about having a seperate signal ground connection in the past, but it does require being very careful to maintain safety and doesn't guarantee anything.
Galvanic isolation does seem very tempting on occasion...
Mark Whitney asked, "Which is it? amp only with inputs shorted or is there an external crossover with a PSU connected?"
The external crossover is passive, between the amp outputs and the speakers, sorry.
Meanwhile, I have found two of my shorted RCA plugs, salvaged from bad crimping, are not fully short! Into the trash they went, now all channels behave the same.
The adcom amps in my stack with above-ground inputs do not like my lifted-ground cables, the amps without do. When I say dislike, I mean 0.25 v of garbage at the speaker terminals. Get rid of the special cables, back to 0.001 v.
The external crossover is passive, between the amp outputs and the speakers, sorry.
Meanwhile, I have found two of my shorted RCA plugs, salvaged from bad crimping, are not fully short! Into the trash they went, now all channels behave the same.
The adcom amps in my stack with above-ground inputs do not like my lifted-ground cables, the amps without do. When I say dislike, I mean 0.25 v of garbage at the speaker terminals. Get rid of the special cables, back to 0.001 v.
Something is bothering me: the other night while testing and listening to the bad noise with the above-ground Adcom amps, the noise on one channel got worse, to the 0.25 v mentioned above, then I smelled faintly something burning. Cut all power, called the wife in and asked if she could smell it, she was not sure. As above, without the raised-ground cables, the 3 GFA-535 II's pass tones and are dead silent, as expected. I may have been "smelling" the audio garbage! Just to make sure, could I, with power off, measure resistance between the 6 total input shields and chassis grounds and expect a consistent reading? I have read elsewhere on this site that it is 100 ohms.
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