Grounding AV receiver

[manofsteel]

Hi
I am experiencing Hum from My subwoofer and think it might be because the AV receiver is not grounded
It has only two pins in the power connector but the shape is the same as an IEC connector

My subwoofer is on the other side of the room so i can't run an extension cable as it will be seen
All ideas and suggestions welcome

Thanks in advance

 

[highfigh]

Hi
I am experiencing Hum from My subwoofer and think it might be because the AV receiver is not grounded
It has only two pins in the power connector but the shape is the same as an IEC connector

My subwoofer is on the other side of the room so i can't run an extension cable as it will be seen
All ideas and suggestions welcome

Thanks in advance

Using an extension cable could be done for testing, though. If you don't do that, it will be difficult to know what to do about the hum. One additional test- find out if the sub and receiver are on the same phase in your breaker panel. Being on different circuits can create enough resistance on the ground that it causes a ground loop and FYI, 'ground loop' is a term used incorrectly far too often.

Look into the IEC connector on the receiver- if it has three pins but a two prong power cord is being used, get the correct power cord and use it.

What brands and models of equipment are you using?

 

[manofsteel]

Using an extension cable could be done for testing, though. If you don't do that, it will be difficult to know what to do about the hum. One additional test- find out if the sub and receiver are on the same phase in your breaker panel. Being on different circuits can create enough resistance on the ground that it causes a ground loop and FYI, 'ground loop' is a term used incorrectly far too often.

Look into the IEC connector on the receiver- if it has three pins but a two prong power cord is being used, get the correct power cord and use it.

What brands and models of equipment are you using?

thanks will get an extension cable now and test. in the process of doing it while i am replying
It is a denon and there are only two pins inside but the shape is like an iec connector

The hum is high and low, its like its fluctuating
The hum is not a constant hum

 

[manofsteel]

The hum is not a constant hum but its up and down

 

[j_garcia]

Is that the cable it came with? Are there other outlets not on the same circuit you can plug the sub into to test? Could be an issue with the outlet the sub is plugged into. If there are any fluorescent lights, or other "noisy" high current gear (fans, fridge, etc...) on the circuit, the sub can pick that up. Did you already check out this sticky?

Ground Loops - Eliminating System Hum and Buzz

You’ve just connected your system and there’s a buzz or hum that won’t go away. You’re running your gear through power conditioners and you’re beating your head against the wall trying to figure out what’s up. Congratulations - you've just entered The Ground Loop Zone...Several weeks ago I was...

forums.audioholics.com

 

[manofsteel]

Is that the cable it came with? Are there other outlets not on the same circuit you can plug the sub into to test? Could be an issue with the outlet the sub is plugged into. If there are any fluorescent lights, or other "noisy" high current gear (fans, fridge, etc...) on the circuit, the sub can pick that up. Did you already check out this sticky?

Ground Loops - Eliminating System Hum and Buzz

You’ve just connected your system and there’s a buzz or hum that won’t go away. You’re running your gear through power conditioners and you’re beating your head against the wall trying to figure out what’s up. Congratulations - you've just entered The Ground Loop Zone...Several weeks ago I was...

forums.audioholics.com

HI
ok I have tried two different surge protectors and made no difference
I connected the subwoofer to the same extension as the receiver using an extension cord and made no difference

The hum is coming when the receiver is off
The only thing connected is the LFE cable from the subwoofer to receiver
wire from the chassis of the subwoofer to the receiver chassis
the power cable on both receiver and subwoofer

Hum is still there
Hum goes high and low

 

[manofsteel]

one thing i have tried is removing the earth from the kettle lead that goes to the subwoofer as a test
the hum is near enough gone

 

[j_garcia]

You mean like a ground lifting plug? Was going to suggest disconnecting all inputs to see if the hum is still there, that would indicate an amp issue. But lifting the ground also tells you that you could have poor grounding as a whole or noise in the line.

 

[manofsteel]

You mean like a ground lifting plug? Was going to suggest disconnecting all inputs to see if the hum is still there, that would indicate an amp issue. But lifting the ground also tells you that you could have poor grounding as a whole or noise in the line.

what could it be bad capacitors?
I have looked at the amp board in the subwoofer, all the caps seem perfect visually

one thing i have just noticed is that if i have everything removed and only power cable connected i hear a slight buzz that is when my head is next to the subwoofer but when i change the phase switch from 1 to 2 it goes quiet but then the other way it is the same buzz

 

[j_garcia]

When my Epik Emprire was dying, it made a sound like that, yes the caps were going bad and it did have a cycling up and down hum right before it died. It was fairly loud though, even with nothing connected to it. My friend reported the same thing with his JBL sub right before it died. A little transformer hum is normal with your ear right up to the driver, but I would not expect to hear an up/down cycling.

What sub and how old?

 

[manofsteel]

it is a rel qbass so pretty old
there are no visual signs of leaking caps

 

[TLS Guy]

We really do have a bunch of slow learners here. We go over this again and again.

This certainly sounds like a ground loop. Now for the umpteenth time a ground loop is caused by a RESISTANCE between grounds.

Now the receiver is not grounded because it is double insulated. The sub is grounded. It also reproduces the bass, and so will emit the loudest hum.

So, where are the other grounds?

The usual suspects are cable systems and ethernet connections. There also could be other grounded equipment connected to the receiver.

So, this is the drill. Unplug everything connected to the receiver except the sub, the speakers and AC cord.

Next question: - is the hum gone? If this is a ground loop it will be gone.

Now connect the cable system back up. Is there hum?

So you connect each input in turn and see which ones bring back the hum.

So any units, or cables that when connected, bring back the hum, have a resistance between their grounds and the ground of the sub.

Once you know that you can go about solving your problem.

It really is that simple.

 

[manofsteel]

We really do have a bunch of slow learners here. We go over this again and again.

This certainly sounds like a ground loop. Now for the umpteenth time a ground loop is caused by a RESISTANCE between grounds.

Now the receiver is not grounded because it is double insulated. The sub is grounded. It also reproduces the bass, and so will emit the loudest hum.

So, where are the other grounds?

The usual suspects are cable systems and ethernet connections. There also could be other grounded equipment connected to the receiver.

So, this is the drill. Unplug everything connected to the receiver except the sub, the speakers and AC cord.

Next question: - is the hum gone? If this is a ground loop it will be gone.

Now connect the cable system back up. Is there hum?

So you connect each input in turn and see which ones bring back the hum.

So any units, or cables that when connected, bring back the hum, have a resistance between their grounds and the ground of the sub.

Once you know that you can go about solving your problem.

It really is that simple.

HI
Thanks for the reply
I have done this

I only have subwoofer and AV receiver connected
The satalaite box was not connected to the AV receiver but i unplugged it from the mains

Could a network switch be causing this even though it is not connected to the AV receiver

 

[manofsteel]

With the receiver unplugged from the wall but the LFE cable plugged in both receiver and subwoofer, there is a hum
the subwoofer and receiver are connected to each other via the chassis

 

[TLS Guy]

With the receiver unplugged from the wall but the LFE cable plugged in both receiver and subwoofer, there is a hum
the subwoofer and receiver are connected to each other via the chassis

So, you now only have the sub cable and speakers connected to the receiver? I don't know what switch you are talking about. Just to make sure, is your TV disconnected from the receiver? Also make sure the providers cable is disconnected from everything. Also unplug ALL ethernet cables.

If it hums then, it is not a ground loop as long as long you are certain the sub is the ONLY ground. It is easy to miss one. If you have hum after you are sure you only have one ground, then it is NOT a ground loop. Then most likely it is some type of RF interference due to the long cable. Belden have a cable that is resistant the RF. Blue Jeans cable will make you one, of the correct length and terminations. To make sure, move your sub as close to the receiver as possible and just connect it with a short high quality cable. If it hums then, you likely have a faulty sub.

 

[manofsteel]

So, you now only have the sub cable and speakers connected to the receiver? I don't know what switch you are talking about. Just to make sure, is your TV disconnected from the receiver? Also make sure the providers cable is disconnected from everything. Also unplug ALL ethernet cables.

If it hums then, it is not a ground loop as long as long you are certain the sub is the ONLY ground. It is easy to miss one. If you have hum after you are sure you only have one ground, then it is NOT a ground loop. Then most likely it is some type of RF interference due to the long cable. Belden have a cable that is resistant the RF. Blue Jeans cable will make you one, of the correct length and terminations. To make sure, move your sub as close to the receiver as possible and just connect it with a short high quality cable. If it hums then, you likely have a faulty sub.

The speakers are not connected
Just the subwoofer
I am using RG6 subwoofer cable at the moment. I have ordered a new cable
It is not a loud hum but it is humming
if it is the subwoofer then could it be caps

 

[TLS Guy]

The speakers are not connected
Just the subwoofer
I am using RG6 subwoofer cable at the moment. I have ordered a new cable
It is not a loud hum but it is humming
if it is the subwoofer then could it be caps

RCA cables are 75 ohm the same as RCA, but the capacitance is different, so this I suppose could be an issue. Either way, move the sub close to the receiver and connect it with a short good quality RCA cable.

 

[manofsteel]

RCA cables are 75 ohm the same as RCA, but the capacitance is different, so this I suppose could be an issue. Either way, move the sub close to the receiver and connect it with a short good quality RCA cable.

I'll Try and bring the subwoofer closer but if the hum is still there but not so loud. Could this be interference from somewhere or is the subwoofer
Upon inspecting the subwoofer there are no bulging caps
The subeoofer is a rel qbass

 

[manofsteel]

One thing I've tried that helped as a test is removing the earth from the kettle lead to power the subwoofer. The hum was very low. Not so loud
Also I tried a ground loop isolator and that got rid of the hum but the volume output quality really low

 

[TLS Guy]

I'll Try and bring the subwoofer closer but if the hum is still there but not so loud. Could this be interference from somewhere or is the subwoofer
Upon inspecting the subwoofer there are no bulging caps
The subeoofer is a rel qbass

Bring it closer. RF interference is now a modern plague, with LED light bulbs, especially when connected to SCR light dimmers, produce huge amounts of RF.

Designers as a whole are not paying nearly enough attention to RF rejection in their designs.