If you know the Shell gas station in Chestnut Hill, Community Audio is right across the street, just before Willow Grove Avenue. When you walk in, the more high-end audio part of the store is in the back (second) room. And, if you go through that back room, into the building behind that main building, you'll find the best stuff.
Hideaway Records, who carries new/used turntables and a bit of used kit, is across from the other gas station in Chestnut Hill, the Sunoco on Bethlehem Pike. Also there is the former Borders bookstore, the terminus of the SEPTA R8 Regional Rail line, and where the trolleys/buses turn around.