The Phono Box RS2 has a rather rare playback option: the mono-era Decca LP EQ curve.
Prior to the mid-1950s, different record companies used different recording EQ curves (emphasis) and expected consumers to use corresponding (de-emphasis) curves when they played back the LPs. Many mono-era "hi-fi" preamps—for instance, the McIntosh C8 "Audio Compensator"—offered a variety of EQ options. Around 1954, the Recording Industry Association of America (RIAA) stepped in and convinced the various US labels to standardize on RCA's "New Orthophonic" curve, which became the…