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Overload protection for speakers

Although the protection circuit is fairly simple, it forms an effective guard against overload of the input of amplifiers and loudspeakers. Why these inputs may need protection now that line levels have been standardized is because there are signal sources on the market that generate outputs of several volts instead of the standardized 1 V r.m.s. Also, in some applications, the loudspeaker signal is applied to the line output of a separate amplifier via a voltage divider, in which case the levels may be well above 1 V r.m.s. The diagram shows a schematic that resembles the familiar series resistor and zener diode. Here, however, the zener is constructed from a small rectifier and a transistor, since commercial zeners appear to start conducting way below their rated values, which gives rise to unwanted distortion. The constructed zener makes a well-defined limitation possible and does not affect signals below the critical level. Configuring T1 as a diode reduces the number of comp…