28 May
2010
28 May
'10
8:34 p.m.
On Fri, 28 May 2010 13:23:21 -0500 (CDT)
"Gabriel M. Beddingfield" <gabrbedd(a)gmail.com> wrote:
On Fri, 28 May 2010, Veronica Merryfield wrote:
Yes, as I go back and read that A was proven by A... it
could be the power source for either device -- and most
likely the "cheaper" card A.
-gabriel
OK, had a bit more of a think.
Once you connect the analogue side of the the USB device to the
installed (high quality card) you have an earth loop that traverses
both the analogue and digital domains. You also have an +5V loop (unless
the USB device is externally powered) This loop does not exist when the
USB card is self testing. I still can't think exactly how, but I
believe this is likely to be a significant part of the problem.
--
Will J Godfrey
http://www.musically.me.uk
Say you have a poem and I have a tune.
Exchange them and we can both have a poem, a tune, and a song.
The 100 Hz (being 2x 50Hz, the power freq. in
Italy)
suggests that it is probably related to some manner of
power supply. However, I have no theory why we're
getting 2x 50Hz (and I think I need one :-)).
The implication has been that the USB audio device is a
cheaper device. It is therefore more likely that the
device runs from the USB 5 volt line than have a separate
power supply, and that 5v line is regulated and therefore
less likely to have a power line ripple on it.