Subwoofer Hum Help - B&W PV1 2 channel setup

[admin_exported]

Recently purchased the PV1 to replace an older mission sub in my 2 channel setup. The current subwoofer connection is via the B&W supplied ARJ45 line level inputs which are fed by my 2 channel amp's speaker outputs. This I understand to be the recommended connection per B&W instructions.

I am experiencing subwoofer hum (not a soft humm but quite a noticeable one) when the sub is turned on. After doing some reseach I believe this is due to a ground loop issue as the PV1 does not have an earth plug on the power cable. To verify that this is indeed a ground loop issue when I remove the connection from the sub to the amp and turn the sub on the hum completely disappears.

The practical solution to this would be to earth the subwoofer to the grounding terminal on my amp so that the sub is not fighting for the ground. However the B&W manual indicates that the sub does not need to be and should not be grounded. I am lost as to what to do but am pretty sure this is the only way to remove the hum. (My previous sub had an earth plug on the power cable and never hummed). Should I ground the sub and disregard B&W's instructions or is there another way around this? Any advice or experience with a similar problem will be greatly appreciated.

PS: I cannot use a grounded 3 pin power cable on the PV1 as the sub only has a 2 pin power cable socket.

PPS: The sub and amp's power cables are all running out of the same wall socket in the wall and I have tried inverting the sub plug but the humm is still there.

 

[Anonymous]

Anyone ?

 

[matengawhat]

things like these are very annoying - think big chris has the same sub

the fact that the sub doesn't make a hum when just plugged in suggests something between amp and sub - you have it wired up the right/recommended way and i am guessing you have double checked the connections/colours at the amp end.

if it is a ground earth problem try connecting a piece of wire to one of the metal screws that looks like its connected to something important - only had this problem once and that was with a video recorder many years a go and I had to tape a piece of wire to the bottom metal base plate and connect to the stand to clear it in the end

 

[Big Chris]

Yep. I do have a PV1, but can't say I've had your problem.

Can you run an extension to a mains socket in a different part of the house? Just wondering if it's picking up interference from the mains.

Also, try running the cable to your amp away from any other cables/wires. Again, it could be picking up some sort of interference.

To confirm colours, it's red to red and black to black on one channel (funnily enough), and green to black and yellow to red on the other channel. (been a while since I've connected it, think I did black/red to the 'R' channel and green/yellow to the 'L' channel, but not sure it matters as it's a mono sub)

Let me know how it goes.

 

[Big Aura]

I had a sub-hum issue that only arose when I upgraded my cheap sub-cable to a chord crimson. Swapped it for another chord crimson, and the issue when away...

 

[Big Chris]

Big Aura:I had a sub-hum issue that only arose when I upgraded my cheap sub-cable to a chord crimson. Swapped it for another chord crimson, and the issue when away...

Only problem is the PV1 comes with a dedicated cable for hooking up to high level/speaker connectors. Unless the OP has an amp with a sub out, he's stuck with what came in the box.

 

[Anonymous]

I have checked all the connections and they are all good. Also played around with using other mains outlets in the house and the annoying hum still exists.

I'm going to ground the sub to my amp's grounding terminals (although its against B&W's operating instructions) and see if it goes away. Anyone have any experiences or know of any good reasons why I should not ground the sub?

Will report back and to see if the grounding eliminates the hum. Yes the amp is strictly 2 channel and does not have a separate sub out.

 

[Anonymous]

I had the same problem with my PV1. Turned out in the end to be the connector on my Sub cable. It wasn't crimped properly. Try another Sub cable if you have one.

 

[Anonymous]

Finally had time to revisit this and am glad to report a resolution.

I replaced the ARJ45 cable (the ones that runs from the amp's speaker outputs to the sub) and the hum is gone. Now I can go ahead and fine tune the sub.

Initial impressions - very controlled and musical but have to say there isn't a bag of bass compared to my old sub which was a Mission 78AS.

 

[proffski]

I resolved a similar problem for a friend by earthing the subwoofer to the nearest mains earth. Complete cure!