Phono Preamplifiers

Rather than engineer a separate MC step-up into its Chinook phono stage Manley has chosen, instead, to provide a unified J-FET/6922EH tube circuit, the latter wrapped around a passive RIAA eq network. Loading is dialled-in via the back panel to accommodate different pick-up types but the gain – pretty much bang-on specification at +45.7dB and +60.3dB – is set via a pair of DIP switches mounted on the main PCB. This is equivalent to input sensitivities of 5.16mV and 966µV (re. 0dBV output), respectively, and while the latter figure won't suit the lowest output MCs, the Chinook still has a trick up its sleeve with its huge headroom.

This preamp has a truly phenomenal 51V maximum output from a respectably low 102ohm source impedance and this, in turn, services a huge input headroom of 265mV (or +34.3dB re. the 5.2mV sensitivity) and 52mV (or +34.6dB via the 0.966mV sensitivity). As a result you simply will not clip/overload or otherwise stress the Chinook regardless of your choice of pick-up or wildest of vinyl groove excursions! The 83.2dB A-wtd S/N ratio is also generous for an MM-focused tube preamp.

Distortion is well managed, increasing with level through the midrange from ~0.0045% up to 1V output, to 0.01%/3.5V and 0.035%/10V. THD also increases at low (0.027%/20Hz) and high (0.042%/20kHz) frequencies [see Graph 2, below] although these figures are still two orders of magnitude lower than those from a typical MM/MC at 5cm/sec. Similarly, the RIAA eq. is unaffected by gain and remains flat within ±0.5dB from 13Hz-45kHz combined with a modest sub-bass filter of –4dB/5Hz. The +3.7dB/100kHz ultrasonic 'kick' is not uncommon but remains well beyond the range of even the most ambitious pick-ups [Graph 1, below]. PM