Another Speaker Hum Question... - AVS Forum
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post #1 of 6 Old 09-01-2012, 11:28 AM - Thread Starter
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I've had a small hum in my speakers for 6 months or so. I haven't wanted to deal with it. Today I spent some time looking at it.

Here are my quick questions (which I didn't see answered in the wealth of other discussions on this topic):

1) Does the pure existence of dimmer switches contribute to hum or do the dimmer switches need to be in use? For example, if the lights controlled by the dimmer are turned off, can dimmers produce hum? I'm thinking no, but wanted to verify
2) Similar for fluorescent lights. Can they cause hum when turned off?
3) It seems that "noisy" devices on different circuits can cause hum. Is this true? (Other threads have implied yes to this, but wanted to triple check)

Now, a little more about my situation:

0) It's a old but trusted HK 525 receiver
1) With all inputs to the receiver disconnected, it's still present
2) The sub doesn't hum
3) With the sub output disconnected, the hum on the main speakers is still present
4) When I turn the volume up louder, the hum gets louder
5) Even though there are no inputs connected, when I change AV source the hum goes away briefly. FWIW, the receiver is pretty slow at detecting the digital mode and this the time where the hum goes away seems to match the digital format acquisition time

The HK525 is suppled with a power cord that does not have a ground plug. With all the inputs disconnected and the hum occurring, as well as the sub output disconnected, I don't see how a ground loop could be a cause.

I'm thinking something has happened to the HK525 or there is noise on the power line. I do not have a snazzy power conditioner.

What do you guys recommend?

The answer to the dimmer question will help as I have about 4 or 5 dimmers for can lights, as well as florescent lights. However, the hum occurs when these when both of these are off.

I'm thinking I'll try the extreme approach and turn off all other circuits.

Thanks!

... Altan

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post #2 of 6 Old 09-02-2012, 05:44 PM - Thread Starter
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Went ahead and did the circuit breaker thing...

With all the other circuits turned off, the hum remains...

Thinking it's either dirty power or just the HK525. What do people think?

... Altan

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post #3 of 6 Old 09-02-2012, 06:11 PM
 
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Quote:
Originally Posted by MadMyers View Post

Went ahead and did the circuit breaker thing...
With all the other circuits turned off, the hum remains...
Thinking it's either dirty power or just the HK525. What do people think?
... Altan

Too many variables. How old is your home electrical system? It sounds like it's a fairly new system. Is the system properly grounded. Is the AVR properly grounded? Today, many units are grounding through the neutral return. I don't like it when that's done. If there's a short to the neutral (white) wire, you could be getting a ground loop that way. That's why I ask how old your house wiring is. My understanding, dimmer switches are more an inductance problem, as can be refrigerators and freezers which can cause GFI fits. Do you have any CFL's attached to the home theater circuit? CFL's kick up their own brand of electrical interference.

You might have a switched polarity where the hot and the neutral are reversed. You can get a outlet tester at a local hardware store in the form of a simple, go/don't go, test light interface.

41ruIGVdvcL._SL500_AA300_.jpg

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post #4 of 6 Old 09-02-2012, 06:19 PM - Thread Starter
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Thanks for the reply.
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Originally Posted by BeeMan458 View Post

Too many variables.

I tried to eliminate many... let's go through your questions and see what's left.
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Originally Posted by BeeMan458 
How old is your home electrical system?
Built in 1993.
Quote:
Originally Posted by BeeMan458 
Is the system properly grounded.
To the best of my knowledge.
Quote:
Originally Posted by BeeMan458 
Is the AVR properly grounded?
Not sure what "properly" means. As mentioned, the AVR supplied plug doesn't have a ground, so it would be using the neutral.
Quote:
Originally Posted by BeeMan458 
Today, many units are grounding through the neutral return. If there's a short to the neutral (white) wire, you could be getting a ground loop that way.
Short between what?
I've used one of those circuit testers (thingies with the 3 lights) and it tests "ok"
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That's why I ask how old your house wiring is. Dimmer switches are more an inductance problem and can cause GFI fits. Do you have any CFL's attached to the home theater circuit? CFL's kick up their own brand of electrical interference.
Not on the home theater circuit. But they exist on another circuit, but the problem occurs when they are turned off and when that circuit is disabled.

Does this info tend to focus the issue?

... Altan

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post #5 of 6 Old 09-04-2012, 10:16 AM
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Unfortunately, your descriptions of the symptoms suggest to me that there might be a problem in the part of the power supply providing power to the preamp inputs of your receiver. Perhaps some of its filter capacitors are starting to fail.

One thing you might try is to short-out the inputs on the receiver that you don't use. I.e. put a jumper wire between the central socket and the surrounding metal of each of the RCA jacks. You might be able to locate some RCA shorting covers at a local electronics or audio/video store. If the hum is being caused by RF interference being picked up by the receiver's internal wires connected to the preamp circuits, this might help -- it forces the input signals to be 0 volts.

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post #6 of 6 Old 09-04-2012, 10:40 AM
 
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Quote:
Originally Posted by MadMyers View Post

Does this info tend to focus the issue?
... Altan

Only that from your above, it reads as if your home electrical system is not the problem.
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