LFM-1 EX Hum

Hopefully someone can help me here.
I got my LFM-1 EX today.I powered it on and turned the volume to max, there is a humming sound with only one end of the subwoofer connected. I didn't connect the other end to receiver. If I turn the knob down, I don't hear the humming sound. When I switch it to X-over active I don't hear the hum.
When I connect the other end to receiver, only on the highest volume I get nice bass from the subwoofer.

Can some one help me please.

Thanks,
Ray.

Sounds like a ground loop hum. Try plugging it into another receptacle. Does it make the noise with the AVR off and the sub fully connected to the AVR with the volume way up? Make sure your sub input cable is not laying parallel to a power cable somewhere.

Is it possible to have a ground loop when the LFM-1 EX cable does not contain a ground prong?

Yes because it has no ground plug it is dependent on the system to be at the same ground across all components. Remember that the cold side of the 120 vac receptacle is tied to the house ground at the breaker box so even without a ground prong the component is still tied to the house ground.

Here is a nice illustration of what happens inside one's electrical panel:



The important details are that the either phase of the hot side could be "seeing ground" across the neutral connection as the neutral from the electrical company meter / service entrance is attached to ground inside the panel.

The folks at Jensen Transformer (who make an OUTSTANDING range of products to electrically filter / isolate A/C power...) have a very thorough pdf that explains all the gory details on how hum gets into systems -- http://www.jensen-transformers.com/an/generic%20seminar.pdf

A simpler overview is also online-- http://www.epanorama.net/documents/groundloop/home_solving.html

These amateur radio guys also have a nice clear explain how to isolate the power if you want to go that route -- http://amfone.net/Amforum/index.php?topic=13605.0;wap2

Thanks renov8r for posting the great info !

So what is the fix or what is the process of elimination to determine if the hum is caused by a ground loop. I spent a lot of time researching subwoofers prior to purchase and very disappointed right now.

I was finally able to check the amp by itself and the woofer by itself and still at a loss for what is causing the hum. Here are my findings:

With amp disconnected from woofer and powered up and volume turned to 10 the amp does not make any abnormal sound (LFE disconnected)
With amp disconnected from woofer and powered up and volume turned to 10 and LFE connected the amp does not make any abnormal sound.
With woofer directly wired as a front speaker it plays without any rattle or abnormal sound.

The problem appears to be a function of pairing the amp with the woofer.

I have sent additional notes to Outlaw, but not sure what is the root cause now.

Are you saying that the woofer wired with just the LFE line out or just the amp outputs it works fine, but if you connect both then that's when you get the hum?

I understand that you have been communicating with our tech Jim. I am sure he will be able to help you with the resolution of this issue, however it does sound like an typical ground hum.

The hum exists as follows:

With the sub plugged in and powered on but no LFE connected it hums and the hum gains in volume when you turn the volume gain up on the sub.

With the sub plugged in and powered on AND the LFE connected it hums louder in volume, relative to without the LFE connected, and also increases in volume as you turn up the volume knob.

If you touch the tip of your finger to the speaker posts on the back of the amp with sub powered and either the LFE connected or disconnected you also hear a humming noise.

If it is truly a ground fault issue is there any device that can be purchased and placed in line to eliminate it? I have plugged the sub into multiple circuits even circuits that run through two different panel boards and have also plugged it into outlets that are the only outlets on a single circuit such as sump pump outlet or my outlet on the wall that is directly wired to the panel board and the noise is still there so I have eliminated the possibility of any other devices on the circuit causing the hum.

I would suggest contacting Outlaw and return it for a checkup.

I second the motion! Sounds like it needs to be looked at by the Outlaws to me, too.