hum, phase, and stubling into improvements

[kkerwin]

hi all,
i have the qa550, mojo monica source,  tube amp and solid state amp for passive bi amping the woofers of my dick olsher, basszilla speakers.  i have always had a bit of what i thought was a ground loop problem that manifests inself in a low hum from my woofers. 

also, i am creating balanced power with a big 2kva tranformer.  the balanced power made some real improvements, but the power has had about 1v difference, so something like: 57-0-58.  anyway, i was reading about ground loops and found somewhere a suggestion to experiment with systematically turning the plugs over to see if there might be an improvement.  i have some pretty stout hospital receptacles, so i couldnt simply turn the plugs over.  so, i took some three prong "cheater" plugs and ground the larger blades down so they would fit in receptavce upside down.  to make a long story short, after a little experimentation between turning over the plug on my solid state and the plug feeding the qa 550/mojonica, i found that the hum was reduced to barely perceptable, and...  to my suprise, the soundstage, and phase became much clearer.
this simple tweak has made a very good difference.

[yeo]

hi kevin

interesting!

i guess this means we should try out a "cheater" plug to see whichever orientation works better. the one that works better is the correct one to go for!

yeo

[kkerwin]

hi yeo,
it's such a simple experiment that it seems worth trying.   my amp is the only component connected directly to earth ground.  the hum i was experiencing really wasn't noticeable at normal listening levels, but it was noticeable when the amp driving the bass speakers was turned up without music playing.  so.. when i tested it, i simply compared how loud i thought the hum was with the different plug orientations.  it was quieter reversed from how i had it originally. this change also seems to have improved the stage. 

[kkerwin]

i would be very curious to know if others notice a difference when experimenting with different plug orientations.
k

[ole]

Yes, of course. Actually, that's quite old. As much as I understand, this has something to do with capacitive coupling from the live side of the mains connection to case and shielding. In case your device uses a transformer, it is more desireable to have the neutral side of the mains connected to the outer winding layer of the primary. Other types of power supplies may also have preferred "polarities".

If you don't want to experiment much, you can use a multimeter for this, see http://www.gcaudio.com/resources/howtos/acpolarity.html.

In general, you will get better ambience and resoluton if everything is correctly plugged.

Ole

[kkerwin]

hi ole,
thanks for the link.  i hadn't run across this before.  i am running balanced power, and it seems like the difference should be all that noticeable, but it does make a difference.
k