Audio Output Meter

This project is a simple VU (volume unit) Meter which you can use to measure the level of audio frequency voltages at the output of an amplifier or oscillator. A sensitivity control is included to allow full-scale Meter readings with audio voltages between about 0.2V and 9V.

The circuit is a simple half-wave rectifier with filtered output which is fed to an adjustable DC voltmeter. An input DC blocking Capacitor is included so that measurements can be made on circuits which have up to 25V of DC present along with the audio AC signal.

We've discussed DC voltmeter circuits in detail in other experiments see Testers Section. To operate the VU Meter simply connect the Probes across the circuit to be measured, taking care to observe polarity if DC is present in the circuit. Adjust the 50K Control for the desired Meter reading.

In circuits where no DC voltage is present, the 10uF Capacitor may be replaced with a short circuit. In these circuits the 47K Resistor may also be removed, and replaced with an open circuit.

The applications for Meters such as this include monitoring the level of audio for tape recorders, radio-stations, TV stations, etc. You may use this circuit to measure some of the oscillators and amplifiers in this kit. The only requirement is that the parts used in this Meter not be required for the other circuit.