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

[Alex Carver]

No, no shorting, just disconnect the ground on each RCA from one side of 
the cable.  You want to keep the shield working but you don't want 
current to flow on the shield.  So choose only one side (could be the 
Yamaha or the Gemini but not both) and cut the shield on each audio wire 
(left/white and right/red) at that end.  Leave everything else intact.

How about some good old fashioned ACII art? :)  I'm going to pick the 
Gemini side, but it works either way:

Yamaha                                           Gemini
RCA-Left Audio Center pin ----------------------- RCA-L Center pin
RCA-Left Shield ----------------------------x x- RCA-L Shield

RCA-Right Audio Center pin ---------------------- RCA-R Center pin
RCA-Right Shield ----------------------------x x- RCA-R Shield


Cut the shield (and only the shield) at the -x x- marks.  Verify that 
you have no electrical connection from the shield on one end of the 
cable to the other.  Leave everything else alone.  If the hum goes away 
you have a ground loop.


On 8/10/2013 15:58, Robert L. Harris wrote:
> So effectively short the 2 center pins to 1 (as if going mono) and then cut
> one of the grounds out completely?
>
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>
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> On Sat, Aug 10, 2013 at 4:41 PM, Alex Carver <agcarver+ale at acarver.net>wrote:
>
>> 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).
>>
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