Crown FM30 - Audio Processor Adjustments; Stereo Generator Adjustments

5–2
FM30/FM100/FM250 User's Manual
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
appropriate pins of header JP1 on the audio processor board. (See section 2.9.) If
you change the pre-emphasis, change the de-emphasis jumpers, JP203 and JP204
on the Stereo Generator board, to match. (See section 2.8.)
5.1.2 Pre-Emphasis Fine Adjustment
Trim potentiometers, R29 and R65, (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 processor 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 measurements.
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 classic single-channel composite stereo waveform at TP301 on the RF Exciter
circuit board. Adjust the Separation control 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.
5.2.2 Composite Output
You can make adjustments to the composite output in the following manner:
❑ Using a modulation monitor