After reviewing the Margules U280-SC 25th Anniversary Stereo Tube Amplifier in my reference system, I also to review their preamp to it. The SF220.15 preamplifier is designed so that its output is a very low impedance, designed to drive any amplifier optimally, solid state or tube. The circuitry is designed to “strap” the input and output stage, avoiding the use of any negative feedback.
