Subwoofer HUM - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 20 Old 02-26-2019, 08:46 AM - Thread Starter
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Subwoofer HUM

I've recently discovered that my dual DIY BMS 18N862 subwoofers are humming.
Its just a slight hum, but its distracting and annoying

Everything is connected to the same wall socket, and its composed by:
- American Audio VLP 2500 - Powers 2 diy subwoofers
- HPA D500 - Powers 2 Atmos speakers
- NAD T758 V3
- HTPC

All electronics have 3 prong cables.

I got this advise in another thread:
Quote:
in a good quality theater system you only want one grounded component and that's usually the receiver.
- Is this a safe approach?

I can add a Hum Destroyer like this one, but i would prefer to remove the problem, instead of just "masking" it.

What would be the safest and preferable solution?
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post #2 of 20 Old 02-26-2019, 09:43 AM
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The receiver is usually the one non grounded item. Most have two prong plugs.

Try connecting a wire between the AVR chassis and all amp chassis. They all need connected together.
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post #3 of 20 Old 02-26-2019, 10:26 AM
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I'd startby eliminating components one by one turning off/on. you'll usually find the culprit. mine was my cable box, i ended up rewiring the mess i had in back and that helped big time. also check your gains.....good luck it is annoying..
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post #4 of 20 Old 02-26-2019, 10:39 AM
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Quote:
Originally Posted by alex vazquez View Post
I'd startby eliminating components one by one turning off/on. you'll usually find the culprit. mine was my cable box, i ended up rewiring the mess i had in back and that helped big time. also check your gains.....good luck it is annoying..
This. I had an annoying hum and found it was from connecting my projector. After you find the offending device you need to figure out why. In my case, the projector was plugged into an outlet that had USB ports on it. Replacing that with a standard outlet fixed the problem.

Tracking these hums down suck. Lots of trial and error ☹️
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post #5 of 20 Old 02-26-2019, 12:24 PM - Thread Starter
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I've done that, and the culprit is indeed the subwoofers amplifier.
I get the HUM with only the amplifier connected.
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post #6 of 20 Old 02-26-2019, 01:23 PM - Thread Starter
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Quote:
Originally Posted by Samps View Post
The receiver is usually the one non grounded item. Most have two prong plugs.
Try connecting a wire between the AVR chassis and all amp chassis. They all need connected together.
The HUM is present with everything unplugged from the socket, except the Subwoofer amp.
The amplifier has a Ground Lift, but it does not seem to have any effect, the hum is still there.

What can i do to remove the hum?

The amplifier power cable is not detachable, so i would need to change the end plug:


Or i could simply buy the Hum destroyer.

Any ideas?
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post #7 of 20 Old 02-26-2019, 01:30 PM
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Do they hum with no signal cable attached? Do they hum with the amp gain turned down?

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post #8 of 20 Old 02-26-2019, 01:59 PM
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My subs were making a low hiss for a while until I realized I forgot to add a LPF. Maybe try that?
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post #9 of 20 Old 02-26-2019, 02:07 PM
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I’m dealing with a similar issue. It’s driving me nuts. I feel like it’s partly a gain mismatch between my avr and sub amp, but not sure how to fix it without setting the sub amp output gain really low.
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post #10 of 20 Old 02-26-2019, 02:47 PM - Thread Starter
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Quote:
Originally Posted by aron7awol View Post
Do they hum with no signal cable attached? Do they hum with the amp gain turned down?
If i reduce the gain, the hum disappears.
With the signal cable disconnected, the HUM is still present.
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post #11 of 20 Old 02-26-2019, 03:44 PM
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Reduce the gain on the amp driving the subwoofers, and increase the input signal to the amplifier, as long as you do not clip the output of the driving device or the input of the amp.
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post #12 of 20 Old 02-27-2019, 04:51 AM - Thread Starter
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Quote:
Originally Posted by michael hurd View Post
... increase the input signal to the amplifier, as long as you do not clip the output of the driving device or the input of the amp.
The amplifier has 3 Input voltages selection: 0,7V, 1V, 1.44V. I'm already using 1.44V.
Is there any other way to increase the input signal?
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post #13 of 20 Old 02-27-2019, 04:58 AM
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Well of course the sub amp is going to look like your problem because your hum is at 60hz and going through the subs. When you unplug the sub amp, you turn off the subs and therefore the hum. That doesn't mean the sub amp is causing the problem. Like I said in the other thread, this is a ground loop hum you're hearing. Because all your equipment has 3 prong plugs, the ground is looping. Power in USA runs at 60hz, so that's the frequency of the hum.

I'd try lifting ground on every single component that's not the main receiver then also try running a wire between each chassis of each component. Short of all that, I'd get that blue jeans isolation transformer I pasted in the other thread. Not that Hum destroyer thing. https://www.amazon.com/dp/B00GG1PK5W This will kill the hum without killing any fidelity in the system.
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post #14 of 20 Old 02-27-2019, 05:04 AM - Thread Starter
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@markmon1 , thank you for your reply, and by the way, i wasn't discarding your advice.
I've just not proceed with the subject in the HTPC thread, as it was not HTPC related.
(by the way, i'm in Europe, not in the US)
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post #15 of 20 Old 02-27-2019, 05:45 AM
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Quote:
Originally Posted by neo_2009 View Post
@markmon1 , thank you for your reply, and by the way, i wasn't discarding your advice.
I've just not proceed with the subject in the HTPC thread, as it was not HTPC related.
(by the way, i'm in Europe, not in the US)
Ah then you can buy the blue jeans cable isolation transformer directly from blue jeans cable who will ship usps international:
https://www.bluejeanscable.com/store...ofer/index.htm (scroll to very bottom).
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post #16 of 20 Old 02-27-2019, 10:10 AM
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Quote:
Originally Posted by neo_2009 View Post
The amplifier has 3 Input voltages selection: 0,7V, 1V, 1.44V. I'm already using 1.44V.
Is there any other way to increase the input signal?

Not really, unless you insert a pad just before the amplifier and increase the output of the driving unit. Do you have any high voltage lines in the walls close to the location of the amp?


Can you grab an extension cord and try moving the amplifier away from the walls temporarily to see if the hum continues at your current settings?
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post #17 of 20 Old 02-27-2019, 10:16 AM - Thread Starter
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Quote:
Originally Posted by michael hurd View Post
Not really, unless you insert a pad just before the amplifier and increase the output of the driving unit. Do you have any high voltage lines in the walls close to the location of the amp?Can you grab an extension cord and try moving the amplifier away from the walls temporarily to see if the hum continues at your current settings?
I don't know how the electric lines are built in the house, but i think so, they are near the wall where the amplifier is.
Yes, i can try that, although only in the weekend, as the amplifier is placed inside a special cabinet, and its impossible to remove it alone.
Thank you for your input.

Regarding the suggestion of having only one grounded component, do you think it can work, and its advisable to do it?
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post #18 of 20 Old 02-27-2019, 10:43 AM
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I took a look at your AVR, you are going from RCA to either XLR or 1/4" in the sub amp. How are the cables or adapters constructed?



If you power on your sub amplifier with no input cable connected to it ( totally isolated from anything else ) does it still cause hum in the subwoofers? I read you had hum with only the amp connected, but was there an input cable connected? If so, try without the cable.



I am not advising you remove a safety ground, that is never a good idea. Having multiple devices with different ground potentials can cause noise issues.
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post #19 of 20 Old 02-27-2019, 11:22 AM - Thread Starter
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Quote:
Originally Posted by michael hurd View Post
I took a look at your AVR, you are going from RCA to either XLR or 1/4" in the sub amp.
On the AVR, the Subwoofer pre-out is connected to this 0,3m Y adapter cable: Cordial CFY

This cable, connects to this 1.5M 2 RCA Male to 2 XLR Male: Cordial CFU.

The XLR male ends goes to the amplifier XLR inputs.


Quote:
Originally Posted by michael hurd View Post
If you power on your sub amplifier with no input cable connected to it ( totally isolated from anything else ) does it still cause hum in the subwoofers?
Yes, disconnected all the XLR inputs, disconnected all other electronics from the socket, so only the sub amplifier was on, with no inputs, and the HUM is the same.
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post #20 of 20 Old 02-27-2019, 11:30 AM
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Quote:
Originally Posted by neo_2009 View Post
On the AVR, the Subwoofer pre-out is connected to this 0,3m Y adapter cable: Cordial CFY

This cable, connects to this 1.5M 2 RCA Male to 2 XLR Male: Cordial CFU.

The XLR male ends goes to the amplifier XLR inputs.



Yes, disconnected all the XLR inputs, disconnected all other electronics from the socket, so only the sub amplifier was on, with no inputs, and the HUM is the same.



Ok, so pins 1 and 3 are connected inside the XLR plug end.



If the hum is with no input cable connected, then I would suggest moving the amp out of it's cabinet with an extension cord when you have help to do so. If that does help, then you may need to relocate the amp.
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