API Audio The Channel Strip, Channel Strip, 2520 Opamp, API 512 C mic preamp, 527 compressor, redesign of the famous 550A EQ (3 bands, each with 7 selectable frequencies), Stereo bus with rotary control solo, SIP, mute, insert, polarity and compressor link, Free patching on the back, External fader jack, Three 7 segment LED VU displays, Int. power supply