Zapco ST-64D SQ MINI 4-Ch. Class D Mini AmplifierThe new Class D Studio MINI Amplifiers. Over the last couple of years Zapco has introduced more than our pure high end SQ Competition amps. We have also introduced a line of great sounding amps in an affordable price range called the Studio series. The Studio D amps are full range Class D amps with great sound, a compact chassis, and more crystal clear power than the competition. Thanks to a brand new technology, we are able use the NXP Class D