Isolated grounding of receptacles for sound equipment

FionaZuppa

Senior Member
The idea is to provide a chassis ground that is as close to earth as possible, rather than using local EGCs or conduits with possibly-noise-laden aggregate leakage currents.

Much modern electronics have no EGCs, so an IG installation would have no effect on those devices.
Mobile gear? Perhaps not if the power to the gear comes from an external power supply. But if the AC is a plug into the gear then most likely it's using a 2CCC + egc cord and the egc is tied to the chassis in some way. If its rack mounted gear then the rack itself should in some way be tied to the egc. But duly noted, external DC power supplies, if made like junk, will also carry AC noise over onto the DC side. I have this odd saying, if the DC power supply does not contain a muRata noise filter, then the supply is junk.

Mobile vs room/rack audio makes quite a bit of difference with this problem. External DC power to audio gear is better than bringing AC power directly into such gear.

But if the sound guy is already calling out the LED lighting, my bet is that from his experience the lighting is throwing off harmonics onto the lines and the audio crud is picking that up. The fix is for the lighting, sound, and electrical folks to have coffee and donuts to figure out what to do (or not do) so that unwanted noise does not get fed out to the ears of the audience.
 

Jamesco

Senior Member
This is an aside.
I was a Musician, having many hours of recording in a studio setting. Most savvy musicians know that most noise issues can be solved by " lifting " the ground on said piece of equipment. That is, it will stop the hum and noise coming over the speakers. One day we spent some time and found one new generation piece of equipment throwing noise back into the line. It was in fact, a Yamaha, SPX-90. What needs to be realized is that a whale of a lot of Solid State gear below the industrial market is Engineered and built very poorly, and it seems to keep getting worse. The Engineers are doing what they " can " do rather than what they should do and its because everything has been " Monetized." Would an isolated ground have worked? We never had one to try out, so I have no idea how they behave under real world field circumstances. Much about the field of Engineering since the 1980s is about them being further removed, separated, and divided from reality. As thus we have a major lot of solid state gear that is very shoddy and in the large performs very badly, and most people are running around thinking its all so cool.
This is a non-sequitur, and its time to call a spade as a spade. When large numbers of Tech people start saying no, this will be a sign that change is on the horizon.
The time wasted is colossal.
I was a Musician, having many hours of recording in a studio setting. Most savvy musicians know that most noise issues can be solved by " lifting " the ground on said piece of equipment.
I assume you mean lift the signal ground/DC B- circuit ground from the AC power EGC equipment grounded chassis.
 

FionaZuppa

Senior Member
I assume you mean lift the signal ground/DC B- circuit ground from the AC power EGC equipment grounded chassis.
The sound guy in the OP is not lifting anything. He's plugging in the gear and using it.
If anything needed to be "lifted off" then it should have been done in engineering phase and incorporated into the design.

Install it all and see what happens. As of now there is nothing up and running.
 

Jamesco

Senior Member
The sound guy in the OP is not lifting anything. He's plugging in the gear and using it.
If anything needed to be "lifted off" then it should have been done in engineering phase and incorporated into the design.

Install it all and see what happens. As of now there is nothing up and running.
My response was to StarCat post #20.

It could be StarCat was talking about lifting the EGC using a ground cheater (3 wire to 2 wire plug in adapter) at the mains receptacle outlet.

Beings you responded to my post, there is a lot audio designers that connect the circuit ground directly to the chassis when an EGC is used. Poor circuit grounding design.... Doing so directly dumps any noise that may be on the EGC onto the signal ground of the piece of audio equipment. It is also more than likely to cause ground loop hum when more than one AC branch circuit is used to feed audio equipment where the audio signal is connected from one piece of audio equipment to another piece of audio equipment by SE interconnects.
Most pro audio equipment uses balanced interconnects.



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zbang

Senior Member
Most pro audio equipment uses balanced interconnects.
Surely, however most also use electronic devices to both drive and received the balanced line (in place of a transformer), and those devices are (a) signal-ground-referenced and (b) don't always have the best balance anyway. If you want real isolation, use a good transformer.
 

GoldDigger

Moderator
Staff member
Surely, however most also use electronic devices to both drive and received the balanced line (in place of a transformer), and those devices are (a) signal-ground-referenced and (b) don't always have the best balance anyway. If you want real isolation, use a good transformer.
And please keep in mind that the balanced-to-unbalanced transformers in the in-line XLR to 1/4 phone adapters are generally very small and good only for mike level signals. They will saturate if you try to use them on line level signals. There is a reason that good direct boxes cost a lot more, they use larger transformers.
 

Jamesco

Senior Member
There are probably things that were not considered when the Amphitheater was first wired. Therein the wiring method used. There is a good chance an EE, audio engineer, was not involved in the electrical wiring design. And more than likely an audio EE was not involved when the type of stage LED lighting was bought and how they were wired into the existing AC power system.

JMHO, maybe an audio design EE should be hired before the OP starts trying to solve the LED noise problem on his own. The LED lighting noise can also be from radiated EMI. Are there dimmers? More harmonic noise.
 

Little Bill

Moderator
Staff member
My response was to StarCat post #20.

It could be StarCat was talking about lifting the EGC using a ground cheater (3 wire to 2 wire plug in adapter) at the mains receptacle outlet.

Beings you responded to my post, there is a lot audio designers that connect the circuit ground directly to the chassis when an EGC is used. Poor circuit grounding design.... Doing so directly dumps any noise that may be on the EGC onto the signal ground of the piece of audio equipment. It is also more than likely to cause ground loop hum when more than one AC branch circuit is used to feed audio equipment where the audio signal is connected from one piece of audio equipment to another piece of audio equipment by SE interconnects.
Most pro audio equipment uses balanced interconnects.





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When you hear "ground lift" in audio, it generally means there is a switch that disconnects the ground. I see them mostly on direct boxes but have seen them on other equipment. Usually they are a toggle switch.
 

Jamesco

Senior Member
When you hear "ground lift" in audio, it generally means there is a switch that disconnects the ground. I see them mostly on direct boxes but have seen them on other equipment. Usually they are a toggle switch.
Which ground? There are, (may be), two.

In home audio equipment the ground lift toggle switch lifts the circuit ground of the audio equipment from the EGC grounded chassis. The safety equipment ground should never be lifted from the chassis of the equipment.

Like I said in an earlier post the circuit ground of the piece of audio equipment should never be connected directly to the EGC grounded chassis. Usually when it is some manufactures recommend the use of a ground cheater on the 3 wire power cord plug to stop a ground loop hum problem. Bad idea. Some will install a toggle switch on the back of the equipment that will lift the circuit ground from the chassis, therein the DC power supply B- as well as the Signal ground.

For the money spent on the toggle switch and the internal wiring for the switch the designer could have just installed a resistor or a diode in series with a resistor, in series between the circuit ground and the EGC grounded chassis.

Audio Research Corp. uses, (used to, still may), a small wattage 10 ohm resistor in series with the circuit ground and the EGC grounded chassis.

Here is how Bryston does it, (used to, still may). Look at the circuit just to the left of the IEC power inlet connector. Note the EGC connects directly to the chassis of the equipment.
https://www.diyaudio.com/forums/power-supplies/161428-variations-dc-main-filter-buzzing-toroid-transformers.html#post2088079

The problem with just modifying an existing piece of equipment, the designer may have connected the circuit ground to multiple points on the chassis.

This may be the ground lift switch you are referring to on old Fender guitar amps.
https://www.thetubestore.com/early-fender-guitar-amp-schematics

I just picked the top one on the list. Note the power cord is a 2 wire with a non polarized plug. See the cap after the switch. They are referred to as a death cap.
https://www.thetubestore.com/lib/thetubestore/schematics/Fender/Fender-Bandmaster-5E7-Schematic.pdf




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PaulMmn

Senior Member
Are there any AM Broadcast stations nearby? Their signals can swamp audio circuits! When I was in high school we set up mikes and stuff for a play, and until the AM station (less than a mile away) went off the air for the night, we had their signal all over the place!

I think judicious use of ferrite beads may have helped.
 
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