This is a design circuit for simple audio wattmeter circuit. This is an easy trick to measure the output of an amplifier. In this circuit, resistor R2 acts as the load for the amp and it should be able to withstand twice the maximum power of the amp you are going to measure. The meter scale must be calibrated and with a little effort you can get good results. This is the figure of the circuit.
Operation of the circuit is if 1A bridges diode is not available, make one with four 1N 4007 diodes. The resistor R2 must be twice the power of amp you are going to measure. To calibrate the device, connect the output of amplifier to port 1. It also connects an AC voltmeter to port 1. Set R1 fully off. That means full counter clockwise direction if wired conventionally. Adjust the output of amp to read 20V rms on voltmeter. This is the equivalent of 50W on 8 Ohm load. Adjust R1 for a full scale deflection on meter M1. Now fix the wiper of preset R1 using some super glue. Reduce the voltage across the port 1 by reducing the output power of amplifier under test according to the table given below and mark the readings on the meter scale. The device is ready to measure.
Operation of the circuit is if 1A bridges diode is not available, make one with four 1N 4007 diodes. The resistor R2 must be twice the power of amp you are going to measure. To calibrate the device, connect the output of amplifier to port 1. It also connects an AC voltmeter to port 1. Set R1 fully off. That means full counter clockwise direction if wired conventionally. Adjust the output of amp to read 20V rms on voltmeter. This is the equivalent of 50W on 8 Ohm load. Adjust R1 for a full scale deflection on meter M1. Now fix the wiper of preset R1 using some super glue. Reduce the voltage across the port 1 by reducing the output power of amplifier under test according to the table given below and mark the readings on the meter scale. The device is ready to measure.
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