The MK IV SE is equipped with a SEPP OTL in class-A circuit design, gold damping rings around all four tubes, and an ALPS-27 potentiometer on the thick front panel. The internal jumper allows for a wider range of tube-rolling fun with equivalents, derivatives, and direct replacements to the existing tubes. As for the sound, this amp/preamp delivers a wide soundstage with extended bass and precise 3D imaging, performing effortlessly with any headphone impedance. After a few hundred hours of burn-in, you’ll experience a markedly smoother sound.