Abstract: To determine apparent power consumption in a distributed-load, constant voltage audio distribution system, a test instrument is provided which is substituted for the amplifier in the system during the test. A constant, known AC test voltage at a convenient audio frequency is applied to the distribution system or a portion thereof. The resultant AC current passing through the distribution system is measured and read on a meter calibrated directly in watts. The apparent power consumed in the system is directly proportional to the current. The instrument is provided with an internal audio frequency oscillator as a test signal source with a provision for bypassing it so that an external oscillator may be utilized. The oscillator signal is processed by a voltage controlled amplifier and a power amplifier wherein the signal level is controlled. The processed test signal is applied to the system under test. The voltage across a resistance in series with the tested circuit is monitored through an isolating buffer.