Sometime ago I acquired a Technics SP-15 deck. I took it, at the time as a
"stand by" and it has been "standing by" waiting for it's big moment to
arrive. A few days ago that moment arrived and I transferred a 78rpm record
from it. As it hit the amp it sounded wonderful, both through speakers and
headphones. As it went through the Tascam CC-222SL and onto CD it sounded
splendid. Play the CD back on the Tascam, Marantz, Pioneer and even the car
CD player and everything is beautiful. Play it back through the computer
(desk top and lap top) and the sounds terrible; very distorted and tinny.
All the more odd is that when I play back from the computer (either the CD
or going in directly through and Edirol interface), through an external amp,
it sounds fine, yet when I turn up the computer speakers at the same time
what comes out of them directly from the computer is very distorted.

Anything else played in the same way through the computers; vinyl from a
Thorens, tape from a Teac, any other CD from the Tascam, radio, DATs,
Minisidiscs etc are all fine. After having tried just about every
permutation of phone leads and sockets that I can think of I am homing in on
the SP-15 deck. The computer seem to doesn't like it directly and though
other CD players and amps are happy playing the test CDs that hold
recordings transferred from the deck, again, the computer is not happy when
it comes to tracks taken from the SP-15. (I created a CD with tracks from
various sources and all played fine in the computer other than those taken
from the SP-15).

I am about to set off and get the deck tested and it might be worth noting
that the power lead goes to an AC Converter as this piece of equipment was
from the U.S.A but now resides in the U.K.

Any advice on what could be the cause or how to resolve this conundrum would
be greatly appreciated.