The Model 503 500 series EQLa, like its counterpart found on the 583e, offers up very low distortion signature and minimal phase deviation; it is an extremely clear and transparent EQ design. Additionally, we’ve added some capabilities to the 503 not found on the 583e, specifically: Cut/Boost range increased to +/- 12dB Low pass filter at 5k & 10k High pass filter at 50hz & 150hz +/- 6dB overall trim gain stage