| 摘要 |
<p>The circuit is applicable to high quality audio amplifiers. It switches off the final amplification stages of a three channel power amplifier. The stages each handle different parts of the auido frequency spectrum. The final stage is a class B amplifier fed from a quasi class A amplifier stage which remains energised continuously as it has a very low quiescent current drain. The power stage is switched automatically when there is no input signal to the equipment. The output of the signal source, for example a tape deck or radio tuner, is applied to a voltage divider and a tapping applies part of the signal to an amplifier driving a relay coil. The relay contacts are in the primary circuit of the power supply transformer for the final stage. With no signal the transformer is off and thus gives a considerable power saving. The power supply for the preamplifier and intermediate stages is taken from a separate transformer which remains energised. Automatic switch off on cessation of signal is time delayed to prevent undesirable interruptions.</p> |
