I agree with replacing the line-stage tubes (12AX7). I struggled with my system suspecting other components,speakers, etc. By serendipity, I came across a matched pair of 12ax7 NOS Mullard equivalents. Needless to say My search is OVER. MAGIC! I suspect that the tubes were not matched in the production of this fine pre-amp. Maybe they are now. But let me tell you I am enjoying the crap out of my system. Hope this helps.
