Why does my Dynamo HUM when amp is turned off?

[remoteportal]

I've hooked my new ML Dynamo subwoofer via the LFE (RCA) to the LFE output (RCA) of my Sony STR-DE475 5.1 receiver.

When I turn off my Sony amp the Dynamo makes a moderately loud humming noise (as if a person were to hum loudly) so I immediately have to flip the power switch off because it freaks me out.

Why does it do this? Is this normal?

I don't think it's related to the power management function because it happens in all three positions (standby, auto, on).

I purchased it used on eBay--it's supposedly only a year old and allegedly in perfect condition.

 

[Kruppy]

Could be a ground loop hum from cable connection. Do you have a cable connection to your receiver? If you do unplug the coax and check you sub.

If this is the problem it is easily fixed with a video isolation transformer like this: http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=180-075

You might want to do a forum search on ground loop hum as there's been a number of very good threads on this topic.

 

[MiTT]

Yep, ground loops are the bane of your existance if you connect a cable feed to your A/V system. Methodology and solution that Kruppy suggested is spot on.

 

[TrumpetDoug]

Dynamo HUM

What a great Zappa tune!!!

 

[JMAUSGP]

My thoughts exactly, watch out for the yellow snow!

 

[tsmooth]

People had have the same issues all the way up to the Descent i, so I believe Kruppy hit this one on the head. Research ground loop on this forum because this issue has been previously discussed in depth.

 

[SundayNiagara]

I'd tell ya to ask Zappa, but he's long-gone!

 

[Kruppy]

People had have the same issues all the way up to the Descent i, so I believe Kruppy hit this one on the head. Research ground loop on this forum because this issue has been previously discussed in depth.

This is by far the easier problem to deal with however, tracking down the offending component/cable can be difficult. I know there are others on the board who have had hum issues not related to ground loops, but the internal sub amp components. Pulling the coax cable is a very simple check, if that isn't it then a systematic check of cables and components (along witht the sub) is in order.