APPENDIX B: HOW IS MEASURED THE AMPLIFIER POWER?measure directly the output voltage on the screen.Precision of the measurement• All the measurement tools (Digital scope and distortion analyzer) have beenrecently calibrated (less than one year).• We’ve made some measurements on some batch of NXAMP to have a clear idea ofthe precision of the amplifier itself, from one unit to the other (small differences inthe manufacturing of the custom transformer of the larges power supplies are themain factor for having different power capability).• The precision on the dummy loads has also been checked with a calibratedohmmeter.Due to all this tolerances, we can compute a value for the power output of each channel ofthe amplifier in a precision of (+/- 10 %).Measurement methodThe input signal is a burst sine wave at 1 KHz, for 20 ms, every 500 ms. We increase theinput level up to reaching 1 % THD+N on the distortion analyzer. We measure the signalwith the scope cursor as shown in the picture bellow:The last one wave of burst signalshall be measured.Close-upThe center of the emission line shallbe adopted as the measurement value.Signal20 msec1 msec500 msecVburstCursorWe do 4 measurements for each output, so we do 16 measurements per unit. Then weaverage on 4 units of NXAMP4X1C or NXAMP4X4C.Then we redo the same with 4 units of NXAMP4X1U or NXAMP4X4U, mains being 120 Volts(+2, -0 Volts at 60 Hz).Finally we average all the measurements and this is the values which are written in thedatasheet of the NXAMP Powered TDcontrollers.PAGE 137 OF 140
