Sony TA-8650

This design, using a paralleled fully complementary V-FET output stage operating in class B, could drive an 8R load at 80W with barely measurable distortion.

A dual FET helps reduce offset drift with temperature. This then feeds two differential stages, the last of which feeds the drive via a current mirror. The complex diode-resistor bias stage eliminates the effect of power supply fluctuations on the quiescent current.

To provide the necessary gate-to-source bias potentials these are connected crosswise and fed from a higher voltage supply. A quiescent current of 400mA was specified (48W per channel). The output devices are matched for Vgs, necessary for uniform current and dissipation distribution, which means that if only one fails, all six must be replaced.

This model had a very extensive and therefore flexible preamp with a wide range of input, output and filtering options.

Attention given to the many mechanical switch contacts and PCB edge connectors can often restore a non-functional unit.

Other lower power (and priced!) versions were the TA-4650 and TA-5650.

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