This circuit will reveal the height level of an input signal placed on a speaker.
It is mainly meant as a fool proof device when linked to an amplifier of higher power rating compared to speaker.
The loudspeaker power indicator circuit is exclusive in this no distinct DC power supply is essential because the circuitry functions through the input voltage to the speaker.
R5 isolates the amplifier's output stage from possible error situations in the circuit. D1 to D4 full wave rectify the input signal and also causing DC is utilized to provide the op amp.
The 741 is employed as a comparator a reference voltage is extracted from ZD3 and fed into the inverting input of the op amp. The non inverting input samples the rectified input signal.
When a peak reaches the loudspeaker power indicator circuit the IC's output goes high and the led flashes. ZD1 stops the LED switching on once the output of IC1 is low as a result of output being ineffective to go lower than 1.5V higher than ground under these situations.
ZD2 describes the upper threshold of the op amp's supply voltage in the existence of large transients whilst R2 acts as the current limit resistor.
It needs to be apparent that the level from which the led lights depends upon the R3 value.
The associated table displays the value needed for this part for various input powers across an 8 ohm load.
If several load values need to be employed for the speaker the value of R3 could be established through the formula: