Discovering the Response Curve of an Amplifier (INS037E)

An important factor in evaluating the quality of an audio amplifier is the knowledge of its response curve. It should be flat between at least 100 Hz and 15 000 Hz for a good quality amplifier. If the curve is not supplied by the manufacturer, we can draw it by using only two instruments, plus a resistor that must have the same input impedance value, a resistor with output resistance and dissipation equal to the power. For this purpose we need the following equipment:

a) Audio generator

b) Audio Voltmeter or Multimeter



The figure below shows how the various test elements should be interconnected.






We initially set the audio generator to a minimum frequency below the audible limit, around 10 or 15 Hz. The signal produced must be sinusoidal.

Then we open the generator level and the volume to have a minimum reading on the scale, the instrument needle begins to move. From there, we increase the frequency of the generator in controlled steps and we will write down the values found in the graph.

The frequencies chosen may be, for example, 20 Hz, 50 Hz, 100 Hz, 200 Hz, 500 Hz, 1 kHz, 2 kHz, 5 kHz, 15 kHz and 20 kHz.

The graph obtained will be similar to the one obtained in the figure below. If there is saturation in the center frequencies of the range, reduce the signal strength and start the tests again from the beginning.