Phono Preamplifiers

Most cartridge brands specify their pick-ups' output with reference to a 1kHz/5cm/sec groove where figures of 3-6mV for MMs and 0.2-0.8mV for MCs are typical. In practice, groove velocities some +18dB higher may be encountered on the 'fiercest' of discs – the longstanding Ortofon 2Ms [HFN Oct '08, Mar '11 and Jun '21] will deliver peak outputs up to 50mV here – so phono stages must be able to accommodate these inputs without clipping further into the RIAA circuit. Because tube preamps offer the possibility of high-voltage gain stages it's tempting for designers to opt for a 'purist' passive RIAA eq network rather than a wholly or partially active RIAA where the equalisation is folded into a tube or transistor feedback stage. But with passive RIAA soaking up a lot of gain these preamps often have limited headroom/input overload margins, as we saw with ModWright's PH 9.0 [HFN Feb '22] and the Zesto Andros Deluxe II [HFN Sep '21].

Instead, PrimaLuna is playing it very safe and very 'compatible' in the EVO 100 Tube Phono where its active RIAA confers very generous input overload margins. For example, the MM input will tolerate up to 250mV before clipping [black trace, inset Graph] – a massive +34dB of headroom over the 5mV output of our hypothetical MM. By contrast the PH 9.0 offers just 14mV of 'breathing room' before distortion hits 1% (a mere +9dB headroom). The EVO 100 Tube Phono is equally generous/tolerant of high MC outputs, offering +38.7dB [blue trace], +34.3dB [green] and +30.1dB [red, all re. 0.5mV MC] with its 'Low', 'Medium' and 'High' gain settings, respectively. This means it'll even accommodate the nominal ~2mV/5cm/sec output of a 'high output' MC, traversing maximum +18dB groove peaks, into its 'High' gain input without clipping. PM