6X-500 500-Series Microphone Preamp and EQ. The 6X-500 from Lindell Audio captures sources with detail and clarity. Inspired by the classic Pultec design, the 6X-500 is a one-channel transformer coupled microphone preamplifier and passive 2-band equalizer in a 500-series format. Feed your signals through an all discrete design based on Lindell Audio's hybrid amplifier, and give them a 15dB boost of some of the richest high end and deep low frequencies for a fast, punchy, in-your-face sound.