Crown PSA-2 - Page 88

Type of Test/ Adjustment
23. Gain
24. Threshold
25. Common Mode
Rejection
Filter Response
27. Noise
crown
Input Signal
Characteristics
IKHz sine wave, 2.1V
applied to balanced inputs
no load
IK Hz sine wave, 2.1V
(output 42 volts) no load
20Hz/ 20K Hz, 2.1V
applied to specified XLR
pins
200Hz and 2K Hz, 2.1V
sine wave; no load
50Hz, ISKHz; 2.1V
sine wave; no load
Variable 20Hz-20K Hz
sine wave; 600 ohm center
tapped resistor
Comments
Adjust Gain controls (R106, R206) for 42 VRMS at
each output
Adjust the Threshold control (R7) fully counter-
clockwise and note the output voltage (it should be approx-
imately I! volts). Move control back to fully clockwise.
Short pins 2 and 3 together of the XLR input jack while
applying the signal to pins | and 2. With a 20Hz input
signal, adjust R101, R201 for minimum output. With a
20K Hz input signal, adjust C102, C202 for minimum output.
Check the CMR Response output; output must be:
70dB below 42V from S5Hz-3K Hz and
55dB below 42V at 20K Hz.
Activate all LO and HI PASS filter switches (SW100,
$W200, SW101, SW201). Apply 5SOHz signal to each chan-
nel. Vary the input signal frequency and make the following
observations: Response should be flat within +1dB of the
center frequency. At the 3dB down point from center
frequency, the frequency should vary no more than +5%.
Follow the same procedure for the ISK Hz high pass filter.
Return filter switches to “flat”.
Insert a 600 ohm center tapped resistor into the
balanced input. From 20Hz-20K Hz, the amplifier output
should be less than .775mV (-60 on V/dB scale). With a
voltage gain of 20 through the main amplifier (see specs),
this corresponds to the -86dBm equivalent input noise.
7-20