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Measure the response at pin 7 of U4. Note in Figure 6 above that the input voltage has not
been changed. (Voltage at pin 1 of J3). The other curve represents the response at the
output of the second section of the filter.
The second section is a moderate Q (Q equals about 2) high-pass filter at 1.9kHz. Be-
cause of the higher Q the filter actually peaks (The 2.1kHz Peak).
Verify the peak frequency, 2.1kHz and the peak voltage 3.2V P/P. Also verify voltages at
40kHz, 20kHz, 1kHz, and 600Hz.
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