[ale] OT: One for the EE's, Amp noise?

[Alex Carver]

On 8/10/2013 14:55, Robert L. Harris wrote:
> So I have a Yamaha RX-A1010 receiver.  It's been great so far but not
> enough volume when we want to have a party, etc.  So I picked up an
> external Amp by Gemini.
>
> When I plug the pre-out from the Yamaha into the Gemini I get a low hum
> that almost sounds like static.  If I plug my DVD player or Phone into the
> Gemini using an adapter ( 1/8th -> RCA ) the noise goes away, crisp clear
> sound.  If I use the Yamaha speaker out no noise either.  It seems to only
> be from the Yamaha to the Gemini.  I can use either of the pre-out ( front
> or surrount ) or the headphone jack on the front and the sound persists.
>
> Any thoughts on how I can clear it up?  The yamaha is out of warranty (
> 2.5yrs old) and a great unit but just too quiet on occasion.

Without actually hearing the sound I'm inclined to believe you have a 
ground loop.  You can test for a ground loop issue by making an RCA 
patch cable that connects only the center pins together and leaves the 
ground on one end unconnected.  If the sound goes away it's a ground 
loop and you just either use that patch cable with the lifted ground or 
get a transformer-based ground loop isolator.

It won't happen on your phone because the phone isn't grounded.  The DVD 
player may have isolation in it (or it may not be grounded at all, 
either, if it's got a two-prong plug).