Pre/Power Amplifiers

The Strumento No1 mk2 preamp includes a very precise stepped attenuator offering, for this most costly method of volume adjustment, an almost unprecedented 100dB working range. The switched resistor network provides adjustment in fine ±0.5dB steps over the top 40dB of its range (+10dB to –30dB), with an accuracy of ±0.03dB, and ±1.0dB steps from –30dB to –50dB with a precision of ±0.1dB. Below this the steps in attenuation increase in coarseness to ±2.0dB, the accuracy (or error) slipping to ±0.5dB from –50dB to –60dB, ±1.5dB from –60dB to –70dB, +3dB from –70dB to –80dB and +6dB from –80dB to –90dB. To derive the full benefit from this stepped volume control, when used with the partnering No4 power amplifier, I would recommend using the lowest of the No1's selectable gain options.

As our inside shot illustrates, the No4 is no less complex in design. It is a fully balanced amplifier with six pairs of bipolar transistors handling the positive-going signals and six pairs for the negative in a bridged configuration (per channel). Each power amp module has no fewer than seven 10,000μF reservoir capacitors per side, amounting to 140,000μF per channel, supplied by an iron-cored 3000VA PSU transformer. Audia Flight uses no fuses in its designs and so all protection – for both power supply and power amplifier stages – is achieved by active current monitoring via the top-facing 'control board'. PM