Thread: Earthing for No Hum

From: Mike A. Anderson (Wichita, KS)

Subject: Thanks Rick!

...We've had plenty of RFI challenges in our church. Each time it traces to

a different culprit. I'm living with a system (worship center) that's been

renovated and added-on to many times prior to my supervision. Of note

lately, I added an EquiTech balanced power AC system (100 amp wall cabinet)

to support all our TV and audio front-end equip. including cameras. Along

with it a new technical ground scenario consistant with EquiTech's

recommendaitons. TV's not up and running yet, but all of the PA power

nusances are gone. Praise the Lord!

Thanks again Rick,

Mike Anderson

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From: Andrew Smithies (Wellington, New Zealand)

Subject: Re: Earthing for no HUM

From: Mike A. Anderson

<"I added an EquiTech balanced power AC system (100 amp wall cabinet)

to support all our TV and audio front-end equip. including cameras.

Along with it a new technical ground scenario consistant with

EquiTech's recommendaitons. TV's not up and running yet, but all

of the PA power nusances are gone. Praise the Lord!">

This is the way to go for earth current (hum loop) control. You don't need

balanced power to achieve these results though. What is important is that

all the mains power loads draw current equally off the phase and neutral power

wires and that there are no mains sourced currents feeding into your earth

system and that all lighting etc power feeds are separate from the PA system.

In TV studios 1V 75 ohm video which is an unbalanced signal is routed all

over the place. (Imagine doing unbalanced audio!) The only solution to

keeping mains hum out of the video is to tie all signal earths to a

'technical' earth and all safety earths to the mains earth connection. The

two earth systems are joined at just ONE point.

ALL EQUIPMENT is specified to be either double insulated or have

appropriate safety earth connections that are isolated from the signal

earth. The objective is to have an electrically clean earth that has NO

power or noise current in it. As there is no current there will be no

voltage, -even if there are some less than idea technical earth

connections.

Most power supply authorities will not permit you to have more than one

earth system in a single room. TV studios here had to get a special

dispensation to do this.

For us audio engineers we power all the equipment off a single power outlet

and kill (metaphorically!) anyone who puts non-audio gear on our power

feeds so that we can limit the earth currents within the PA system. This

also means any patchpanels, junction boxes, DIs etc must not connect with

the building ground. ie The lighting power box case must not touch the amp

rack!

As there invariably will be something causing earth currents, we have to

deal with that in some other manner. Here are 2 big winners:-

-Bond all earths together in a star system with lots of copper to reduce

the impedance. V=IR and so if R=0 then V=0. R will not be 0 so V will still

be greater than 0. Take note of where the mains earth is in all this. It

matters.

-Use balanced circuits. The balanced mic inputs on your desk looks at the

voltage between pins 2 and 3 for the audio. If their is mains hum that is

equal on both pins then the audio recovered will be unaffected. With

actively balanced inputs this is limited to voltages less than +-15V (The

15V limit depends on the desk) I saw somewhere here discussion on resistors

in 1/4 jack to XLR cables. This improves the impedance ballance and is very

worth while when there is lots of earth currents or volts about.

Please note that I have not made any comments about RFI. Radio signals have

to be treated differently as the cable behave as transmission lines. That

is, The current and voltage is not constant along the wire.

The above is how to deal with HUM.

Andrew Smithies

Wellington

New Zealand

Work: Design Tech: Broadcast Communications Ltd

Church: Assemblies of God.

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From: Mike A. Anderson (Wichita, KS)

Subject: Re: Earthing for no HUM

Andrew,

You provide sage advice, not to mention correct, regarding grounding / earthing

practices. In most applications or situations what you describe will very nicely

suffice for hum elimination. However, we must all keep in mind that exceptions

can and do get presented which defies what is nearly always a successful result.

I knew the grounding scenerio in our building was abismal before I even

began to "buzz hunt". What I found was worse than abismal. The

building(s) have been renovated and added-on to several times over nearly

100 years. The current worship center was completed is 1962, and fairly

thoroughly face-lifted in 1978 (about 2 years before I took up the cross of

lay-tech dir.) About 4 years ago we completed construction on a 50k sq.

ft. Christian Life Center which includes a commercial kitchen, large

swimming pool (read that BIG pumps and high CFM ventilation equip), bowling

lanes, etc. All this "fun stuff" ended up putting so much garbage on the

AC it seemed I would never get away from it.

I started at ground (pun intended) zero. Since we were gearing up for TV,

I used that as a good argument for basically re-wiring the entire PA. Some

of what I found induced night-sweats and siezures - get the idea?! Hum

problem got a lot better. Then I installed the tech ground scenerio and

balanced buss loads at the panel. Hum problem got a little better. Then

we started a major expansion of our theatrical lighting facilities for both

TV and Christmas/Easter productions. I knew this would happen, hum got a

lot worse. We basically do not have the option of getting more/different

AC into the room due to where the complex service entrance is located and

the maze of archetectural barriers between here and there. Trust me, we

checked this out thoroughly.

I first considered simply feeding a common isolation transformer with a

branch circuit and installing a load center for PA and TV down stream of

that. Talked to a lot of seasoned professionals, sometimes that does it,

sometimes it doesn't. Next stop........EquiTech. I first talked to them

and then several balanced power users, including some big-time studios

doing a lot of digital stuff. I was encouraged by EVERY experienced

balanced-power user that I couldn't go wrong. To bring this tome to a

conclusion, the EquiTech system went in, and the hum went packing...it's

flat gone. The panel cost us a little over $5000 plus shipping. The

audible improvement is much greater than anything else I've done since I've

been involved. What else can I say?

I plan to incorporate the panel we now own, along with another one, into

the new worship center (3000 to 3500 seats, 2 or 3 years away from start).

One for FOH and TV, and the other for platform electronics incl. all

keyboards, drums, instrument amplifiers, etc. Both panels and the load

center feeding the amp rack(s) will share a common tech ground scenario.

Maybe in a totally new worship center where everything is done to one

standard, correctly, this would be overkill. But I know it will work; the

rest of the nightmareish complex WILL be isolated from the PA and TV.

Thanks for your interesting read.

Mike Anderson

Immanuel Baptist Church

Wichita, Kansas

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From: Janet Smith (Byron, GA)

Subject: Re: earthing

I have a question when he is talking about earthing is he talking about

grounding ? I get confused when he talks about "tie all signal earths to a

'technical' earth and all safety earths to the main earth connection" ?

Until then I understand if he is talking about grounding.

Janet

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From: Mike A. Anderson (Wichita, KS)

Subject: Re: earthing

Janet,

Yes, earthing is grounding, but specifically a direct path to a good

quality copper-clad rod (8 to 10 feet long) driven into compacted or

undisterbed soil. It is recommended, and I did, go the extra mile and

drive TWO rods at least 6 feet apart and connect to both in series. Then,

VERY important, go directly to the buildings earth ground and terminate the

run there. This insures that your technical equipment also retains

adequate safety ground. If the buildings earth ground is not practically

accessible, it is acceptable to attach to the buildings structural steel

per NEC (National Electrical Code) methods. I had to go the structural

steel route as I'm not sure enough copper has been mined to get me to the

buildings earth point.

There's much more to all this, if you have more questions ask!

Mike Anderson

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