Moving-coil loudspeakers generally provide a substantial improvement in linearity when current driven, together with the elimination of voice-coil heating effects. Consequently there is a need to investigate low-distortion power amplifier topologies suitable for this purpose. After considering established current feedback approaches, a novel method using a common-base isolation stage is outlined and extended to show a prototype amplifier circuit in detail. In addition, the elements of a two-way active current-driven system are described, with low-frequency velocity feedback control derived from a sensing coil. The coupling error between this coil and the main driving coil is nulled by electronic compensation.
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