MB Quart XA1-600.4 600W 4-Channel X-Line Series Class SQ A/B Amplifier MB Quart Xa1-600.4 600 Watt RMS X-Line 4-Channel Car Stereo Amplifier Affordable high-end amplifiers with striking design Elaborate preamplifier with extended control Q-Stasis preamp stage with wide input range Class SQ A/B topology designed by Lukas Lowe