The output of a PC sound card was set to be a 1-kHz sine wave with an amplitude of 1 V using MATLAB. The outputs were monitored with an oscilloscope and ac voltmeter.
(a) For the left channel, the rms value of the open-circuit output voltage at 1 kHz was measured to be 0.760 V, and it dropped to 0.740 V with a 1040- load resistor attached. Draw the Th´evenin equivalent circuit representation for the left output of the sound card (i.e., What are vth and Rth?).
(b) For the right channel, the rms value of the open-circuit output voltage at 1 kHz was measured to be 0.768 V, and it dropped to 0.721 V with a 430- load resistor attached. Draw the Th´evenin equivalent circuit representation for the output of the right channel.
(c) What were the values of the measured amplitudes of the two open-circuit output voltages? What percent error was observed between the actual voltage and the desired voltage as defined by MATLAB?
(d) Go to the lab and determine the Th´evenin equivalent output voltage and resistance for the sound card in your laptop PC.