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ARC SP3 schematic

Posted by JJ Analog on September 19, 2002 at 11:12:01:
Can anyone tell me where to find a schematic for the Audio Research SP3A preamp? Is anything on the Web, or does ARC sell them?
I am trying to track down some hum in the line section (its not the phono as the hum level does not change with volume setting.) Also changing tubes, cables etc. has no effect. It is not the amp (hum goes away with shorting plugs in amp.) I am thinking a power supply cap may be going, but need to see if that could only affect the line stage (separate supplies for line and phono?)