Orban OPTIMOD 6200, Operating Manual

Page: 136 / 195

5-2
TROUBLESHOOTING Orban Model 6200
Problems and Possible Causes
Always verify that the problem is not the source material being fed to the 6200, or in
other parts of the system.
RFI, Hum, Clicks, Or Buzzes
A grounding problem is likely. Review the information on grounding on page 2-10. The
6200 has been designed with very substantial RFI suppression on its analog and digital
input and output ports, and on the AC line input. It will usually operate adjacent to high-
powered transmitters without difficulty. In the most unusual circumstances, it may be
necessary to reposition the unit to reduce RF interference, and/or to reposition its input
and output cables to reduce RF pickup on their shields.
The AES/EBU inputs and output are transformer-coupled and have very good resistance
to RFI. If you have RFI problems and are using analog connections on either the input or
output, using digital connections will almost certainly eliminate the RFI.
Poor Peak Modulation Control
The 6200 ordinarily controls peak modulation to an accuracy of ±1% when operated
with 48kHz output sample rate. As explained in Section 1, output sample rate conversion
will slightly compromise this control because the peak control occurs with reference to
individual sample values at 48kHz. The converted samples no longer have the same peak
values as the 48kHz samples, and some values can be slightly higher. However, the
overshoot of the converted signal almost never exceeds 0.5dB and is therefore not a sig-
nificant problem.
Using the analog output will cause similar amounts of overshoot because the samples in
the transmitter are not synchronous with the peak-controlled samples in the 6200. Fur-
ther, analog connections can cause analog-domain overshoot if the connection is not
phase linear and has a low-frequency cutoff of greater than 0.15Hz (at –3dB).
Audible Distortion On-Air
Make sure that the problem can be observed on more than one receiver and at several
locations.
Verify that the source material at the 6200's audio inputs is clean. Heavy processing can
exaggerate even slightly distorted material, pushing it over the edge into unacceptability.
The subjective adjustments available to the user have enough range to cause audible dis-
tortion at their extreme settings. Advancing the
FINAL LIMT control too far will inevita-
bly cause distortion. (Distortion is very probable if gain reduction in the final limiter fre-
quently exceeds 6dB.) Setting the
LESS-MORE control beyond “9” will cause audible
distortion of some program material.