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Author Topic: California Hummin'  (Read 10154 times)

Steve M Smith

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Re: California Hummin'
« Reply #20 on: May 30, 2014, 05:18:05 pm »

Have you checked your home outlets to determine there are no hot/neutral swaps ?

Why would that make any difference?


Steve.
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Kevin Graf

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Re: California Hummin'
« Reply #21 on: May 30, 2014, 06:21:54 pm »

Have you checked your home outlets to determine there are no hot/neutral swaps ?
Why would that make any difference?
Steve.
If Neutral current flows through the Safety Ground wire there will be a voltage drop (up to about 3 Volts). The means that the chassis voltage on some components can be different than the voltage on other component's chassis. We know that current will take all available paths and a handy path is through the signal cables.
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Mike Sokol

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Re: California Hummin'
« Reply #22 on: May 30, 2014, 08:24:21 pm »

Mike had proposed a GFCI "adapter" that used a capacitor to short emi/rfi to ground-not sure where he is at on getting it "approved."

I'm still playing with it, but it could be a reasonable solution for situations just like this. The problem is that "electrically safe" and "code compliant" grounding doesn't guarantee quiet audio. 
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Stephen Swaffer

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Re: California Hummin'
« Reply #23 on: May 30, 2014, 10:02:56 pm »

Um, there may be other issues if the amp chassis is tied to the hot wire.  :o



May be?  In high school , I had my dad's Eico 5 watt tube amp hooked up in my room, usually setting on a metal shelf.  It had one side of the 120 V line tied to the chassis and no polarized plug.  I learned pretty quick that there was a good way and a bad way to plug it in! Nowadays, I'd be a bad parent if I let my son do the same.

Hot/neutral swaps are a different issue from tying the neutral to the "safety" ground.  Just did a corrective job on a home with an interesting twist.  Roughly half the receptacles had the ground pins up and half had them down, but every receptacle in the house had the neutral on the left side as you face them....so all that had the ground pin up had hot and neutral swapped.  My guess is they were trying to make everybody happy?  In any case, hot/neutral swaps are quite common, so it would pay to double check.  Might make a difference, might not, but when chasing an elusive issue best to eliminate anything that is not just right.
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Mike Sokol

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Re: California Hummin'
« Reply #24 on: May 30, 2014, 11:24:00 pm »

Have you checked your home outlets to determine there are no hot/neutral swaps ?If Neutral current flows through the Safety Ground wire there will be a voltage drop (up to about 3 Volts). The means that the chassis voltage on some components can be different than the voltage on other component's chassis. We know that current will take all available paths and a handy path is through the signal cables.

Actually, that would be a Neutral/Ground swap, which is really hard to find without a load and voltage-drop test. That mis-wiring can cause a current modulated hum, which will do weird things like produce a ground-loop hum that follows the beat. It's what I call GLID (Ground Loop Inter-modulation Distortion).
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Mike Sokol
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Steve M Smith

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Re: California Hummin'
« Reply #25 on: May 31, 2014, 01:22:02 am »

Actually, that would be a Neutral/Ground swap

That makes more sense.  Apart from putting the fuse in the neutral line, A live/neutral swap just reverses the connection to the transformer primary and would not be a cause of hum.


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Mike Sokol

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Re: California Hummin'
« Reply #26 on: May 31, 2014, 07:39:21 am »

That makes more sense.  Apart from putting the fuse in the neutral line, A live/neutral swap just reverses the connection to the transformer primary and would not be a cause of hum.


Steve.

That's correct... simply reversing the live and neutral won't normally cause any hums. However, a H-N reversal is really dangerous for an electrician or technician working on any "live" gear. I've actually experienced this in an industrial situation and had one of my electricians take a big shock when he reached inside a live machine panel that was plugged into a portable cord and touched the "neutral" which was actually "hot". Of course, you can easily find a "hot" neutral with a NCVT or measuring with a meter between "neutral" and a known earth ground. 
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Mike Sokol
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Kevin Graf

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Re: California Hummin'
« Reply #27 on: May 31, 2014, 09:11:39 am »

Putting a stand alone fuse in the Neutral is very dangerous.  If the unit then has a failure (other than directly to the Safety Ground) there is no path to trip the building circuit breaker.  But on the other hand, interlocked Hot & Neutral circuit breakers are safe.
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Jerome Malsack

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Re: California Hummin'
« Reply #28 on: May 31, 2014, 05:44:01 pm »

Another item top look at is the apple products.  They Have non polarized plugs and are connected to various systems that do have the polarized plugs.   

I had the Sony Pre/Pro with a polarized plug connected to a power strip and connected the first Gen Apple TV to the same power strip.  I did an AC voltage check from shield to shield on the RCA connecters and found 10 volts AC. 

With the RCA being a connection to the Common on the Sony.  Should the Apple device be allowed to connect with 10 volts AC transfer to my unbalanced audio?   I check and reverse the plug for the lower voltage on the shield to shield connection. 

« Last Edit: June 02, 2014, 08:34:22 am by Jerome Malsack »
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Kevin Graf

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Re: California Hummin'
« Reply #29 on: May 31, 2014, 06:43:11 pm »

The App;e products probably come under the Class II Appliance insulation code.

http://en.wikipedia.org/wiki/Class_II_appliance#Class_II

I recall that some 30 years ago, one of the Apple products may have had a  accessory jack with a 120V pin. But I don't know if this is truth or myth.
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Re: California Hummin'
« Reply #29 on: May 31, 2014, 06:43:11 pm »


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