Solved! Kef Kube10b subwoofer humming

[lewisblack]

I have just bought a Kef Kube10b subwoofer which is attached to a Yamaha 7.1 RXV671 receiver / amp. I have Kef front, centre and surround speakers. My previous old Pinnacle subwoofer gave up the ghost and blows the 1amp slow fuse when plugged into power. Anyway, the Kef sub hums but only when connected (with audio cable) to the amp and the hum increases in volume when you increase the volume on the sub itself. I have tried; 3 different cables, run the power cable to other outlets and moved the sub away from any other electrical components. Still the same problem... After this I got a replacement new sub (as I thought this was the problem) but still humming! GRR I'm beginning to think it is the amp that has the fault, but before I spend $$$ on a new amp - any other ideas, suggestions or comments would be greatly appreciated. Thanks!

 

[americanaudiophile]

You probably have a ground loop. If the subwoofer has a 3 prong AC plug you can try a 3-2 adapter to break the ground. Another option is to use an audio isolator in between the receiver sub out and sub input. Pretty common issue. Some subwoofers use 2 prong AC cords to avoid the problem.

 

[lewisblack]

Thanks for the response. But the sub only has a 2 prong AC cord. It is plugged into a separate outlet from the rest on the equipment which is plugged into a surge protected power bar. As I understand the audio isolator would only correct this problem if the issue was a ground loop, which ir doesn't appear to be.

 

[lewisblack]

Okay, think I have found the problem - not resolved yet, but I know what is causing the hum - YAY!

I won't bore you with all the details but it appears to be the cable box that is causing the hum. With the cable box disconnected, no more hum. I will be getting onto my cable provider (Shaw) to see what they can do to fix issue.

NOTE: Even with power off to the cable box it still hums. You need to physically remove either the HDMI input (to the amp) or disconnect the coax cable to the cable box. I would suggest if you have similar issues, trying disconnecting hardware connected to your amp one by one...

 

[Kenton82]

Test the Sub output of the AV Amp with another active speaker unit. You could also test with nothing else connected to the AV amp, other than one source - to eliminate another unit being the cause.

 

[lewisblack]

Test the Sub output of the AV Amp with another active speaker unit. You could also test with nothing else connected to the AV amp, other than one source - to eliminate another unit being the cause.

Thanks Kenton82 for your reply. I think I found the issue (posted just before your suggestion) its the TV cable connection

 

[americanaudiophile]

It IS a ground loop problem caused by a bad ground in the cable system. You can use one of these
https/www.amazon.com/TII-220-Ground-Isolator-applications/dp/B0070Q6URO/ref=pd_lpo_vtph_23_tr_t_2?_encoding=UTF8&psc=1&refRID=M52AJM21QSV9K7ZKWJ4C
or contact the cable company. There may be a bad ground where the cable enters your home or building.