Pre/Power Amplifiers

The HD Preamp's watchface indicates the available preamp gain rather than absolute level with '25' representing –30dB (in/out); '50', –11dB; '75', +5dB; and full volume +12dB or x4, even if the '100' legend is just beyond the arc of the needle. Below about '70' on the display the HD Preamp acts as an attenuator, only offering gain above this position. The control confers fine ±0.5dB steps over the top 42dB of its range with ±1dB steps over the middle 16dB and coarser ±2dB-3dB steps across the lower 30dB.

The total useable range is 89dB. The preamp's default frequency response is discussed in the Lab Report while the profiles of the six 'boost' (red) and five 'cut' (black) bass/treble tone settings are illustrated on the inset Graph. As a rule of thumb, the boost settings suggest frequencies of 50Hz and 20kHz (ie, +2 equals +2dB/50Hz re. 1kHz) while the 'cut' profiles operate closer to 20Hz and 25kHz (except '–5'). A subtle but broad adjustment is evidently possible using the ±1 and ±2 settings, allowing a useful tailoring of deep bass and high treble, compensating for room and ancillary equipment the 'old fashioned' way! PM