The Electrocompaniet preamps, like the 4.5, 4.6 and 4.7, are great used balanced pre's that work very well with ATC active speakers. Remember, many of the ATC's (like my ATC 150 pro actives) present a fairly low 10k ohm impedance, so any hi-impedance pre's (like most tubes) will not be a great match. It's somewhat of a conundrum, though, becuase the accuracy and detail of the ATC architecture wants for a nice warm preamp. Solution is to find good neutral/warm pre's in the 100 ohm or less family, and Electrocompaniet fits the bill (the 4.7 is balanced for sure).
