do you have an iPod, or other mp3 player or any other audio device that you
can hook up to the preamp, just to see if you get a better result ? If so,
you should of course keep the output level of the mp3 player very low at
least to begin with, and gradually increase the volume. Because it will be
a line level signal to the preamp, it will overpower it quickly, but it may
give you a hint as to what is going on..... could possibly eliminate
defects in your turntable or the cable that you made, as all of that would
be bypassed for the experiment...

just an idea... report back please...

James