WhitakerAudio JC Whitaker 20 W Stereo Integrated Audio Amplifier, Manual

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–2 dB. Note that in order to accurately measure frequencies below 200 Hz and above 10 kHz
it will be necessary to change the range switch on the voltmeter.
5) Set the audio generator to produce 1 kHz at 0.0072 V rms. Adjust the Volume control to
produce 2.8 V rms at the speaker terminals. Connect a distortion analyzer to the speaker
output terminals. Measure the THD. A reading of below 0.5 percent is typical.
6) Measure the THD at 30 Hz and 100 Hz. For each setting, reduce the generator output to
produce 2.8 V rms at the speaker terminals (do not adjust the Volume control). A reading of
below 0.5 percent is typical.
7) Measure the THD at 10 kHz. Increase the generator output to produce 2.8 V rms at the
speaker terminals (do not adjust the Volume control). A reading of below 0.5 percent THD
is typical. Next, change the generator frequency to 20 kHz, but do not increase the output
level. Instead, increase the Volume control to produce 2.8 V rms at the speaker terminals. A
reading of below 0.75 percent THD is typical.
8) Reduce the output level of the signal generator to 0.0072 V rms. Set the frequency of the
generator to 1 kHz. Adjust the Volume control to produce 2.8 V rms at the speaker
terminals. Adjust the audio voltmeter so the meter reads 0 dB. Remove the generator
connector from the right channel phonograph RCA connector and insert a shorting plug.
Measure the residual noise, which should be –60 dB or greater.
9) Repeat Steps #1 through #8 for the left channel. Similar results should be obtained.
This completes the performance measurements on the preamplifier board.
7.2 Power Amplifier Performance Measurement
Measurements should be made on one channel at a time; the input terminals of the channel not
being measured are shorted. For the measurements, an 8 Ω 10 W (or greater) noninductive
resistor must be connected to the output terminals of each channel. Use the following settings:
• Connect the generator output to the Line input RCA jacks on the back panel.
• Set the Input switch on the front panel to Line Input.
• Set the Volume control to full clockwise.
• Set the Balance control to center travel.
• Set the Bass and Treble controls to flat response.