Ground loop hum with speaker level connections

[marneyj]

Hi everyone,

 

I know this topic has been covered everywhere extensively however I cannot find the answer to my specific question.

 

I recently replaced my amp with an NAD C326 BEE - I now realise my old amp was uneartherd (2 prong plug) and this new one being earthed is causing a ground loop and making my Polk SW12 Sub hum annoyingly.

 

It's a simple 2.1 stereo set up with Wharfedale Diamond 6R bookshelf speakers. The only 2 RCA outs I use on the amp go to my laptop and a bluetooth receiver. The hum is only present when the amp is switched on. The hum is present regardless of whether these are plugged in / switched on / laptop charging etc.

 

I've tried different power points etc.

 

Everything I read suggests the powered sub and amp are causing a ground loop and that placing a ground loop isolator / subwoofer isolation transformer in the line level connection between the amp and sub will break the loop.

 

However I have my sub connected using speaker wire to the high level / speaker inputs (speaker outs on the amp to the speaker ins on the sub / speaker outs on the sub to the speakers).

 

I'm using 14 gauge speaker wire with bare ends to spring clips on the sub and binding posts on the amp.

 

Is there a way to break the ground loop and keep using the speaker level connections between the amp and sub?

 

Thanks for your time,

Marney

 

[MLXXX]

53 minutes ago, marneyj said:

Everything I read suggests the powered sub and amp are causing a ground loop and that placing a ground loop isolator / subwoofer isolation transformer in the line level connection between the amp and sub will break the loop.

 

However I have my sub connected using speaker wire to the high level / speaker inputs (speaker outs on the amp to the speaker ins on the sub / speaker outs on the sub to the speakers).

This is an obvious question. Why have you decided not to use the line-level sub-woofer output of your integrated amp? 

[marneyj]

Hi,

Thanks for replying  - To my ears the speaker level connections sound better and also I'm genuinely curious if it's possible to keep my current set up without having to use the line level connection and purchase an isolation transformer.

 

 

[MLXXX]

Speaker level connection is intended as a backup method, if there is no line level subwoofer signal.  If you really wish to persist with speaker level output it is conceivable you could avoid audible hum by connecting the chassis side of the amp outputs direct to the main speakers and not to the subwoofer, but without a knowledge of the circuitry inside the subwoofer unit that could be dangerous. I would not do that.

What I would try is to use one of the RCA line level sub-woofer outputs using a cable with the outer braid connection open circuit. That might stop audible hum. Using such a cable, the outer braid would connect either to the amp or the subwoofer but not both. Only the inner conductor would connect the amp to the sub.

[Fenda]

I had a similar problem with a hum, it ended up being one of those remote control power switches that wasn't even on the same circuit causing the hum from the amp