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RE: Audio Research SP9 MK2

Posted by amioutaline? on December 23, 2008 at 17:34:22:
If you have some amp building experience, it's not very difficult to upgrade the coupling and output caps.

For the line stage section, Couplers are .47uF Wonder Caps (white)by-passed with .01 Wonder caps. The outputs are 5uF REL caps (yellow), also by-passed. Remove them along with all the by-passes (leave the 2 .01s on the bottom of the board) and replace with your fav flavor. Big improvement.

The 2 electrolytics are now old and Chris at ARC recommends replacing them now.

Don't fool with the diodes, with fancy diodes you will probably get too much voltage drop on the filaments. On that subject, on the bottom of the board are 2 paralleled WW resistors, prob'ly a 50 and a 75Ohm. Check your filament voltage. The resistors run hot (the board is prob'ly darkened there) and your voltage may well be too high as the Rs go out of spec. Replacing with the same values will cure but you may have to play with the values.

Biggest bang is to replace the horrid Alps pot with a TKD or PEC, but not a trivial excercise. I had to cut back the solder pins on a TKD to just below the perforations in the pins and run teeny-weeny, short wires from those holes to the board eyelets while I was suspended from the ceiling to leave my hands free

Remove the toroidal transformer from the side of the case and replace it after fixing EAR SD-40 damping layer to the case.