Speaker/Subwoofer hum (pretty sure it's not ground loop/100% sure it's not broken speakers) - AVS Forum
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post #1 of 15 Old 03-24-2013, 05:57 AM - Thread Starter
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Hello.

I want to start that I've read the FAQ's and guides and quite a bit of old threads on this forum but non of them resolved my issue. I will walk you trough the process which I went trough and try to be as detailed as I can. My reciever is JVC RX-5032V, hooked up to a pair of Harman/Kardon TS11 home theather audio system. I noticed a hum coming from my subwoofer, googled it and bunch of threads came up (most of which in this forum hehe) that pointed to the ground loop. Although we use 2 pin connectors in my country (and the ground loop seems to be an issue in countries using 3 pins) I started experimenting, plugging out different cables/changing the outlet/leaving only the subwoofer and amp plugged but none of it worked. I don't remember at which point (since all of this took me a good couple of hours to read all the info, go trough the manuals and etc.) I decide to turn up the volume - the hum does go louder with it and then I start noticing the same strange hum coming from my speakers as well. After quite a bit of experimenting the only thing left was my amp and two speakers plugged in. Here is how my amp looks from behind at the moment. I still hear the humming noise from the speakers. Here are answers to some questions from another topic in the forum which seem pretty revelant:
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Could try to isolate the cause. Is the noise the same as you change from one source to another (with all of them paused, of course)? Does the noise change when all the source units are powered off?
Yes the noise changes trough different channels. It is the same trough VCR/CD/TV but goes louder trough DVD. FM/AM channels are with the most noise. If I turn up the volume to maxium I can even hear the station I am tuned to (very low volume with distortions) although I don't have an antenna plugged in!
Quote:
Does the AVR have some DSP modes operating, or room EQ? If so, does the noise remain the same as these are switched off?
It had, turning them off did lower the humming down.
Quote:
Does the AVR offer an analog bypass option? Same noise there?
It does have an option for digital. Humming is different and a bit louder I think
Quote:
Does the AVR include an FM tuner? Is it tuned to a station or just plays interstation noise when you select it? (Some AVRs leave the tuner on all the time so it can output to a second zone. If it is playing noise, maybe the crosstalk is becoming audible.)
It does. As I mentioned above the FM is audiable without an antenna when pumping up the volume.

And finally a very strange thing I noticed. Say I plug in my iPhone in the CD source and play some music . The CD source works as expected but if I change the source to say DVD and pump up the volume I can hear the music that is playing trough the CD source - very low volume with white noise. This goes for all other sources except the FM channel trough which I continiue to hear the radio station.

I have this theory that it all has to do with the FM since the volume of the hum is louder in the DVD source and as you see from the picture it is closer to the FM out. My guess is that my sources get intermingled and I hear low volume from all the other sources no matter which one is selected, and the hum is just the sound of the FM constantly on picking up some distrubances. However I am no music expert and I only reached to this conclusion trough pure trial and error - that's why I'm asking for your advice on what to do. I would love to not have to open the amp because I have never opened one before and I can't afford replacing it if something breaks but I am pretty confident with opening up my PC and other electronics so I will do it if very necesary.

If you have any further questions I would be happy to answer them. Thanks in advance for your help smile.gif

PS: I forgot to mention the reason I'm sure it's not the speakers is because I tried different ones and they did the same thing.
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post #2 of 15 Old 03-24-2013, 10:05 AM
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It is very possible that you have a bad ground connection in one or more of your interconnect cables going into the amplifier. The speakers and speaker wires are a non-issue.

I would try disconnecting one set of interconnects at a time and see what happens. As a matter of fact, I would disconnect ALL inputs to the receiver and see if the hum is still there.

If it is still there, it may be a defective power supply in the receiver. If it goes away with all inputs disconnected, then reconnect one at a time until it comes back.

Oh; also try disconnecting the TV from the receiver and see what happens. The TV might have a grounding problem.

I would also try connecting the metal chassis of your receiver directly to a water pipe or some other point that is grounded directly to the AC power bus in the electrical panel.
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post #3 of 15 Old 03-25-2013, 12:13 AM - Thread Starter
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Like I said I have already tried to disconnect everything but the speakers and the hum is still there and I have tried all variants of outlets and etc.
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post #4 of 15 Old 03-25-2013, 06:03 AM
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Quote:
Originally Posted by lumensone View Post

Like I said I have already tried to disconnect everything but the speakers and the hum is still there and I have tried all variants of outlets and etc.

This appears to be your sub?

http://www.harmankardon.com/resources/Brands/harmankardon/Products/ProductRelatedDocuments/en-US/ServiceManual/HKTS11%20sm.pdf

page 5.

Does the subwoofer hum when its volume is turned all the way down?

If so, how about its input cable disconnected?

Have you tried running a different cable from the AVR to the sub?
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post #5 of 15 Old 03-26-2013, 05:07 AM - Thread Starter
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Yes this is my sub. No it doesn't hum with the volume all the way down. When the cable is disconnected from both sides it doesn't hum as well. No I haven't tried with a different cable

PS: The subwoofer let's out a "woof" when you turn the volume down to zero or turn off the AVR
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post #6 of 15 Old 03-26-2013, 05:12 AM
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Quote:
Originally Posted by lumensone View Post

Yes this is my sub. No it doesn't hum with the volume all the way down. When the cable is disconnected from both sides it doesn't hum as well. No I haven't tried with a different cable

PS: The subwoofer let's out a "woof" when you turn the volume down to zero or turn off the AVR

The next logical step would be to put a ground isolator in series with the RCA cable from the AVR to the subwoofer:

http://www.radioshack.com/product/index.jsp?productId=2062214



They are composed of two independent channels so it is permissible to hook up just one set of leads (white or red) at a time.

They can be susceptible to external hum fields and when this happen the hum field can be excluded by putting the ground isolator into an empty tin can such as a tomato paste can.



Just wrap some some wadded up paper towels around the ground isolator and stuff it into the can so that it doesn't rattle around.
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post #7 of 15 Old 03-26-2013, 11:05 AM - Thread Starter
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Is there any way to be sure the ground loop is to blame before buying this? I also don't even have a RadioShack or anything of the like in my country so it will be some searching, plus extra money. That's why I want to be sure before buying it
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post #8 of 15 Old 03-26-2013, 08:40 PM
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If the subwoofer is connected to power, but has no interconnect cable connected (i.e. it is not connected to the receiver) does it hum and does the hum increase and decrease when you raise and lower the volume?

If yes, then the problem is the sub.

If no, locate it near the receiver and plug both amp and sub in and connect them to each other, but connect nothing else. Does it hum? Does the hum raise and lower with the volume on the back of the sub? Does the volume of the hum raise and lower with the volume of the receiver?

Also, do you have any lighting dimmers or neon lights in the room? If so, does the hum persist with lights off?

B.
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post #9 of 15 Old 03-28-2013, 11:23 AM - Thread Starter
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No if the subwoofer has no interconnect it doesn't hum.

I have plugged them in the same plug (only them I removed everything else) trough 2 extend cords . It does hum. The hum does increase with the gain on the back of the sub. It doesn't increase with the amp volume.

No I don't have any light dimmers nor neon lights
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post #10 of 15 Old 03-28-2013, 11:51 AM
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Quote:
Originally Posted by lumensone View Post

Is there any way to be sure the ground loop is to blame before buying this? I also don't even have a RadioShack or anything of the like in my country so it will be some searching, plus extra money. That's why I want to be sure before buying it

Your forum info gives no clues as to where you live or else I'd try to find an equivalent closer to you.

But they are available from many sources in many countries. For example:

http://www.maplin.co.uk/ground-loop-isolator-33172



http://www.ebay.com.au/itm/CAR-AUDIO-STEREO-RCA-NOISE-FILTER-GROUND-LOOP-ISOLATOR-/280598056850#ht_3502wt_1397



...etc...
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post #11 of 15 Old 03-28-2013, 08:15 PM
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Quote:
Originally Posted by lumensone View Post

No if the subwoofer has no interconnect it doesn't hum.

I have plugged them in the same plug (only them I removed everything else) trough 2 extend cords . It does hum. The hum does increase with the gain on the back of the sub. It doesn't increase with the amp volume.

No I don't have any light dimmers nor neon lights

So it doesn't hum when it is disconnected from the amp and raising and lower the level on the sub makes no difference under this circumstance...

Does the sub amp have a 2/3 prong cord? Can you connect it temporarily with the ground removed and see if the hum goes away? If it does that would seem to point to the ground loop isolator solving the problem.

Is the cable shielded? Does it have a separate ground connection?

B.
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post #12 of 15 Old 03-30-2013, 07:29 AM - Thread Starter
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Quote:
Originally Posted by Brian B View Post

So it doesn't hum when it is disconnected from the amp and raising and lower the level on the sub makes no difference under this circumstance...

Does the sub amp have a 2/3 prong cord? Can you connect it temporarily with the ground removed and see if the hum goes away? If it does that would seem to point to the ground loop isolator solving the problem.

Is the cable shielded? Does it have a separate ground connection?

B.
Correct. 2 prong cord. It's just a regular purple cable going from one SUB to SUB output.. I am not sure if it is shielded or not (there is black insulating rubber over it of course but I'm not completely sure what do you mean by that smile.gif
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post #13 of 15 Old 03-30-2013, 09:28 AM
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From what I can see in the photo attached in your 1st post, it appears that the cable in the "sub out" isn't a standard RCA/Cinch plug. That may be your problem.

Even if I am incorrect, get a good shielded coax cable for your sub For example:
http://www.monoprice.com/products/product.asp?c_id=102&cp_id=10236&cs_id=1023603&p_id=2682&seq=1&format=2
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post #14 of 15 Old 03-31-2013, 02:25 AM - Thread Starter
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My cable looks exactly like that
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post #15 of 15 Old 03-31-2013, 02:30 PM
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If it's not a ground issue, then the problem is the receiver. If you can change out the sub cable and it still hums then that is all that is left. You could try putting the cable temporarily in the tape out (make sure the sub level is lowered) and see if the hum continues...

B.
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