Help troubleshooting loud buzz from passive subwoofer - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 17 Old 03-21-2020, 08:03 PM - Thread Starter
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Help troubleshooting loud buzz from passive subwoofer

Hi all,

Been troubleshooting this for a couple weeks with no luck, hoping someone here could shed some light or ideas. Setup is as follow:

-Denon X6200 -> Art Cleanbox Pro (coax) -> Peavey CS4000 (XLR) -> JTR Captivator (speakon)

When I turn it on and turn up the knob on the peavey, there is a loud hum/buzz. And I mean really loud, not something subtle. It could be in my head, but it seems like the buzz gets louder as seconds go by. Here is a short video where I turn the Peavey on and then dial it up to 25%:

I've tried a few troubleshooting steps so far:

-Hooking powered sub straight to X6200. This was fine
-Using an SMS-1 instead of Art Cleanbox Pro. This buzzes the same
-Using an EP4000 instead of the Peavey. This also buzzes.
-Trying bridge and non-bridged mode on both amps. All setups buzzed.
-Taking off one end of the speakon and hard wiring it to the bridge speaker binding posts (versus a speakon end cable wired for bridge)
-Randomly plugged the speakon into the second port on the JTR (I think its for daisy chaining), and this also buzzed.


Any ideas?

Last edited by bmrowe; 03-21-2020 at 08:09 PM.
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post #2 of 17 Old 03-22-2020, 08:26 AM
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You have ground loop. Grounding the units to each other using some spare wire will fix this. Alternatively, using the same power outlet for your amps should fix this.
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post #3 of 17 Old 03-22-2020, 08:36 AM - Thread Starter
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Quote:
Originally Posted by bimmaguy View Post
You have ground loop. Grounding the units to each other using some spare wire will fix this. Alternatively, using the same power outlet for your amps should fix this.
Thanks. Loudest ground loop I've heard. The receiver is in a media closet about 70 ft away so using the same outlet isn't an option. Are you saying just ground the amp and cleanbox to each other?
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post #4 of 17 Old 03-22-2020, 08:42 AM
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Ground loop is loud, ugly to listen to and probably not great for your equipment. It blows.


I would probably try the Denon and the Peavey first.



Remove one of the chassis screws and wrap a piece of wire (speaker wire, whatever) around the screw then screw it back in. Attach that wire in the same way to the other amp and the problem should go away.

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post #5 of 17 Old 03-22-2020, 08:54 AM
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Should this fail, 70 feet might be long enough that your cables could be picking up electronic interference. It might be long enough to donate the downtime to being an antenna for SETI. Do you live in a warehouse?



You should get a big beefy shielded RCA (or whatever you're using) cable for that super long run, or maybe move the equipment closer.


Probably ground loop, though.


Good luck!

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post #6 of 17 Old 03-22-2020, 09:24 AM - Thread Starter
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Thanks for the ideas. I'm not able to run a cable that long or relocate anything. When the house was built, they built a media closet that has the whole home automation and all the wiring. The media room with the sub is on the complete opposite side of the house.

Will something like bluejeans cable's isolation transformer or similar have a big impact? https://www.amazon.com/Transformer-E.../dp/B00GG1PK5W
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post #7 of 17 Old 03-22-2020, 09:41 AM
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Well, that's not a setup I would choose, for a variety of reasons, but I'm sure it has a high WAF and very low noise.

In your particular case you should probably try the bluejeans unit. It might be your fix. Worst case, $50 gone.(Still way too much, I'm sure there are cheaper ones)



However, it does say in troubleshooting that it wont fix power lines running next to signal cables. Chances are the electrician did what electricians do and ran all the cables (power included) not only parallel, but possibly through the same small hole in the studs, for a good part of the run. To complicate things more, there would be multiple power outlets (wires) physically touching signal cables for varying parts of the run. Do you notice noises from the sub when your air con or refrigerator turn on? You might not even notice if they are soft-start designs. How about your microwave?


It usually comes trough the speakers as a pop on start and power down, sometimes accompanied by the hum getting louder while the unit is on, or a warbling or harmonic added to the normal buzz. This is a demon I have fought before.

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post #8 of 17 Old 03-22-2020, 09:53 AM
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Another idea... if you have a spare speaker terminal from media room to electronics room, use that. Connect the ground wire to amp A to one of the speaker terminals, then connect at the other end and attach to amp B.

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post #9 of 17 Old 03-22-2020, 10:16 AM
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Quote:
Originally Posted by bmrowe View Post
Thanks. Loudest ground loop I've heard. The receiver is in a media closet about 70 ft away so using the same outlet isn't an option. Are you saying just ground the amp and cleanbox to each other?
It's best to start with the basics first.

It you're plugged in to two different outlets, first make sure that the polarity is correct at the outlets.

An outlet should be wired such that the HOT lead is connected to a specific side of the outlet, and the neutral lead to the other. This is done for safety reasons. Switches on the things you plug into the outlet will open and close the HOT side, so when the switch is off, there will be no voltage inside the device.
The HOT side, should be the smaller of the two openings on the outlet. The neutral will be the wider of the two. Cords where it matters will have one of the prongs wider so the neutral side and hot side line up correctly.

How can you tell? Use a voltmeter, and check the voltage between the narrow opening and the ground opening. It should measure about 110-125V. Measure the voltage between the wider opening and the ground. It should be zero. If your readings are reversed, your polarity is reversed.

If you have reversed polarity at one of the outlets, you'll get a ground loop hum.

If you find that the outlets are correct, try reversing the plug on either the Denon or the Peavey and the Art Cleanbox Pro. You can also try a "cheater plug adapter" to lift the ground.

Since the problem is not present with the Art Cleanbox Pro out of the connection path, I suspect the problem is in the XLR connection termination, i.e. shield/ground pin connection.

BTW, based on the input sensitivity of the Peavey (1.84v) and the 1.2v output of the Denon, I'm not sure there is a significant benefit or need to use the Art Cleanbox Pro. The difference is 3.7dB and I doubt that you will hear any significant difference without it.
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post #10 of 17 Old 03-22-2020, 10:33 AM - Thread Starter
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Quote:
Originally Posted by b curry View Post
It's best to start with the basics first.

It you're plugged in to two different outlets, first make sure that the polarity is correct at the outlets.

An outlet should be wired such that the HOT lead is connected to a specific side of the outlet, and the neutral lead to the other. This is done for safety reasons. Switches on the things you plug into the outlet will open and close the HOT side, so when the switch is off, there will be no voltage inside the device.
The HOT side, should be the smaller of the two openings on the outlet. The neutral will be the wider of the two. Cords where it matters will have one of the prongs wider so the neutral side and hot side line up correctly.

How can you tell? Use a voltmeter, and check the voltage between the narrow opening and the ground opening. It should measure about 110-125V. Measure the voltage between the wider opening and the ground. It should be zero. If your readings are reversed, your polarity is reversed.

If you have reversed polarity at one of the outlets, you'll get a ground loop hum.

If you find that the outlets are correct, try reversing the plug on either the Denon or the Peavey and the Art Cleanbox Pro. You can also try a "cheater plug adapter" to lift the ground.

Since the problem is not present with the Art Cleanbox Pro out of the connection path, I suspect the problem is in the XLR connection termination, i.e. shield/ground pin connection.

BTW, based on the input sensitivity of the Peavey (1.84v) and the 1.2v output of the Denon, I'm not sure there is a significant benefit or need to use the Art Cleanbox Pro. The difference is 3.7dB and I doubt that you will hear any significant difference without it.
Thanks. I'll test the outlets today. I've ordered a cheater plug as a short term way to verify the problem. I used the cleanbox or the sms-1 because the subwoofer cable terminates at the wall as a coaxial with an F-connector. I wasn't finding a cable that went from F-connector to XLR (and isn't it wrong to take unbalanced to balanced with just a cable?). So I did F to RCA into cleanbox and then XLR out of the cleanbox into the Peavey. Happy to try an F/XLR cable if that is a thing just to eliminate one more variable.
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post #11 of 17 Old 03-22-2020, 11:07 AM
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Quote:
Originally Posted by bmrowe View Post
Thanks. I'll test the outlets today. I've ordered a cheater plug as a short term way to verify the problem. I used the cleanbox or the sms-1 because the subwoofer cable terminates at the wall as a coaxial with an F-connector. I wasn't finding a cable that went from F-connector to XLR (and isn't it wrong to take unbalanced to balanced with just a cable?). So I did F to RCA into cleanbox and then XLR out of the cleanbox into the Peavey. Happy to try an F/XLR cable if that is a thing just to eliminate one more variable.
I assume you're using xlr to rca cables. @notnyt has given the solution to this issue.

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post #12 of 17 Old 03-22-2020, 02:11 PM
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Quote:
Originally Posted by bmrowe View Post
Thanks. I'll test the outlets today. I've ordered a cheater plug as a short term way to verify the problem. I used the cleanbox or the sms-1 because the subwoofer cable terminates at the wall as a coaxial with an F-connector. I wasn't finding a cable that went from F-connector to XLR (and isn't it wrong to take unbalanced to balanced with just a cable?). So I did F to RCA into cleanbox and then XLR out of the cleanbox into the Peavey. Happy to try an F/XLR cable if that is a thing just to eliminate one more variable.
No, it's ok to do that. You don't have to use the cleanbox to change genders.

F to RCA > RCA/XLR

Make sure the center wire on the coax/RCA center is connected to pin 2 on the XLR. The coax shield should connect to pins number 1 and 3 on the XLR connection.

You can also change the F to an RCA connector and avoid the RCA/F adaptor if you like. It's not hard to do but the F to RCA adaptor should not be a problem either.
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post #13 of 17 Old 03-22-2020, 02:13 PM - Thread Starter
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No, it's ok to do that. You don't have to use the cleanbox to change genders.

F to RCA > RCA/XLR

Make sure the center wire on the coax/RCA center is connected to pin 2 on the XLR. The coax shield should connect to pins number 1 and 3 on the XLR connection.

You can also change the F to an RCA connector and avoid the RCA/F adaptor if you like. It's not hard to do but the F to RCA adaptor should not be a problem either.
Thanks! I'd have to buy a cable regardless. Got any recommendations for where to find a cable wired the correct way?
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post #14 of 17 Old 03-22-2020, 02:19 PM
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Thanks! I'd have to buy a cable regardless. Got any recommendations for where to find a cable wired the correct way?
XLR Male to RCA Female Adapter

https://www.parts-express.com/xlr-ma...apter--240-438
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post #15 of 17 Old 03-22-2020, 02:37 PM - Thread Starter
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Oh, duh. I'll give it a shot along with the isolation transformer. Fingers crossed!
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post #16 of 17 Old 03-22-2020, 03:22 PM
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Oh, duh. I'll give it a shot along with the isolation transformer. Fingers crossed!
You shouldn't need the transformer if what you've said in the original post is correct. That is, "-Hooking powered sub straight to X6200. This was fine".
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post #17 of 17 Old 03-24-2020, 07:06 PM - Thread Starter
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So the cheater plug got here first. And y'all were right, ground loop. So the hum is gone on the chain: X6200w->cleanbox pro->peavey->captivator. The adapter b curry mentioned will be here tomorrow - curious to see how things perform when I remove the cheater plug, add the adapter and remove the cleanbox.
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