Crown FM150, User Manual

Page: 60 / 110

5.1 Audio Processor Adjustments
5.1.1 Pre-Emphasis Selection
Select the pre-emphasis curve (75 µsec, 50 µsec, 25 µsec, or Flat) by jumpering the appro-
priate pins of header HD1 on the audio processor/stereo generator board. (See section 2.9.)
If you change the pre-emphasis, change the de-emphasis jumpers, HD201 and HD202 on
the audio processor/stereo generator board, to match. (See section 2.8.)
5.1.2 Pre-Emphasis Fine Adjustment
Trim potentiometers, R23 and R63, (for left and right channels, respectively) provide for fine
adjustment of the pre-emphasis. Set the potentiometers to bring the de-emphasized gain at
10 kHz equal to that of 400 Hz. (At the proper setting, 15.0 kHz will be down about 0.7 dB.)
When making these adjustments, it is important that you keep signal levels below the proc-
essor gain-control threshold.
A preferred method is to use a precision de-emphasis network in front of the audio input.
Then, use the non-de-emphasized (flat) output from the FM modulation monitor for meas-
urements.
5.2 Stereo Generator Adjustments
5.2.1 Separation
Feed a 400–Hz sine wave into one channel for at least 70% modulation. Observe the clas-
sic single-channel composite stereo waveform at TP301 on the RF Exciter circuit board. Ad-
just the Separation control R244 for a straight centerline.
Since proper adjustment of this control coincides with best stereo separation, use an FM
monitor to make or confirm the adjustment.
5-2 FM30/FM150/FM300 User’s Manual