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Measure the response at pin 1 of U2. Note in figure 4 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 fourth and final section of the filter. The output is fed to the low frequency
power amp that essentially has a flat response from 20Hz to 20kHz.
The fourth section is a moderate Q (Q is a little more than 1) low-pass filter at 1.4Hz.
Verify voltages at 100Hz, 1kHz, 2kHz. and 4kHz.
If the response is incorrect check values of R53 - R55, C28 and C33.
Reattach lifted lead of C18.
Bias Set Procedure
The following steps are necessary to set the bias on the Power15 amplifier module, PCB
510-00007-XX rev (any).
1. Connect a 4 ohm load (250 watts) to the red and black leads of the amplifier.
2. While maintaining 120VAC, 60Hz, turn the unit on.
3. Set the signal generator to 85 to 200Hz, and to 0.2 Vrms approximately.
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