Pre/Power Amplifiers

When purse strings are relaxed, the high-end audio designer has several routes open in the quest for the ideal 'analogue' volume control. Beyond a high quality film potentiometer there's always the option of a switched attenuator using a ladder network of resistors to offer precisely calibrated 'stepwise' control. Then there's the transformer route, realised in its most simple form as a purely passive control offering some +6dB of voltage gain at the expense of a high and variable output impedance.

Luxman may use a pair of transformers in the CL-1000 but its 'LECUTA' (Luxman Electronically-Controlled Ultimate Transformer Attenuator) is closer in execution to the volume control regime used in Nagra's HD PREAMP [HFN Nov '18]. Here a tube line buffer (employing E88CC triodes) is combined with a transformer employing 34 secondaries that are switched in combination to provide very fine adjustment in volume. A further E88CC-based line stage, with super permalloy output coupling transformers, delivers a more consistent output impedance, and though ~480ohm is still on the high side, the CL-1000's extended frequency response remains less sensitive to volume position than is typical with transformer-based preamps. PM