Phono Preamplifiers

Our lab tests of the Decade Jubilee illustrated the long but steady evolution of Lehmannaudio's phono stage 'concept', a journey that began (for us) with the original two-box Decade but reaches another level of refinement here with the Phonolith, built into the same 'Decade' casework and partnered by the very similar PWX II LZ power supply. The essence of this high gain/passive RIAA circuit is retained in the Phonolith, yielding exceptionally low 0.0004-0.003% distortion [see Graph 2, below] and very wide 88.8dB and 77.7dB A-wtd S/N ratios in its MM and MC settings, respectively. The response too is extended at HF (+0.14dB/20kHz and -1.2dB/100kHz) but includes a gentle bass roll-off that reaches -0.8dB/20Hz before offering an 8dB attenuation at 4Hz [black trace, Graph 1]. Extra subsonic filters are included in the Phonolith, notionally at 32Hz [blue trace], 50Hz [green] and 78Hz [red], so if you have large reflex-loaded loudspeakers and a number of warped LPs, one of these settings will surely prevent you from getting into trouble!

At the time of writing, Lehmannaudio's manual and website rather undervalue the features on offer - quoting just four (36dB, 46dB, 56dB, 66dB) gain options. In practice there are six, three in MM mode (+35.5dB, +45.4dB and +55.6dB) and three in the MC setting (+56.1dB, +66.1dB and +76.0dB), these offering input overload limits of 168mV for all three MM settings and 15.7mV for all three MC settings. These represent headrooms of +20dB or more for all MM and MC gains relative to their respective input sensitivities (re. 0dBV output) - enough to prevent clipping with 99.9% of LPs. Finally, the maximum output is a high 8.95V from a moderate 51ohm source impedance. PM

Above: RIAA-corrected frequency response from 5Hz-100kHz re. 0dBV (black trace, with alternative subsonic filters at 32Hz, blue; 50Hz, green; 78Hz, red)>

Above: Distortion versus frequency re. 0dBV from 5Hz-40kHz (MM ‘0dB’ gain setting)>