18-03-2019, 01:37 PM
Over on diyaudio.com, in a long-running thread about a Cambridge audio A3i, someone has suggested that I'm confusing DC offset with quiescent current, but, in both that amp, and the NAD in this thread, in practice they surely amount to the same thing, since, in both cases the speaker(s) re connected between the emitters of the o/p devices and ground, thus the voltage, obviously in millivolts, measured at the o/p transistor emitters will be the same as that measured at the speaker terminals, and the current through the o/p transistors with no signal i/p is the Iq. The main differences between the two circuits are that 0.22R emitter resistors are factory fitted to the Cambridge amp., but not the NAD, and that pre-set adjustments are incorporated into the Vbe multipliers of the A3i, but the corresponding resistors in the NAD are of fixed value. All this aside, if, e.g., 50mV is measured at the junction of the o/p transistor emitters, then 50mV will also be measured at the speaker terminals. This is what I've always understood to be the DC offset, and, where emitter Rs are fitted the Iq will be that flowing through those resistors, usually ca. 30-50mA in amplifiers of this type.
