Phono Preamplifiers

While interest is inevitably focused on the REF Phono 3SE's RIAA, Columbia and Decca phono eq options there's also an intriguing 'high voltage' theme going on under the lid. ARC's use of close-coupled low-noise FETs for the phono input marks an alternative to tube phono stages combined with step-up transformers, but the use of three 6H30P double-triodes per side also endows this phono stage with truly mammoth input overload margins. As an aside, feedback is modest, so THD is low through the bass/midrange at ~0.0015% but increases closer to 0.15% at HF [see Graph 2]. Otherwise, the real story begins with the +51dB 'Low' and +73dB 'High' gain settings which, although either may be configured with a 47kohm or 50ohm-1kohm input load, are probably best viewed as 'MM' and 'MC', respectively.

The practical gains are +50.4dB and +73.0dB (balanced out), conferring sensitivities of 3mV and 0.224mV (re. 0dBV output). This, and the respective A-wtd S/N ratios of 83.5dB (re. 5mV) and 73.5dB (re. 500µV) suggests it'll handle everything from high o/p MMs down to very low o/p MCs. While these noise figures are short of state-of-the-art they remain better than any through-groove rumble figure and, moreover, conceal the phenomenal headroom that's 'baked in'. While some phono stages exceed 1% THD with a limited 15-20mV MM input [HFN Sep '21 and Feb '22], the REF Phono 3SE will soak-up 295mV (MM) and 21.5mV (MC) before clipping [Graph 1]. Not only does this represent a massive +35dB margin (+20dB would suffice for a 5mV-rated MM pick-up tracking the most violent grooves) but – with that +50dB gain in tow – results in a maximum balanced line output voltage of... drum roll... 93V! Do I need to say this? Never drop a stylus into a groove with your preamp's volume wound up... PM