Audio Developments AD149 User Manual
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LIMITER CALIBRATION
Refer to page 61, #1 for use of external test equipment.
Switch off the limiter and set the presets for Release, Attack and Threshold to the
centre. Set the bias preset on the main PCB - labelled SET 0 on FIG 6 - to its centre.
Apply a 1kHz signal to the channel for a reading of 0dBu at pin 101 indicated on FIG
6. Turn SET 0 preset counter-clockwise until the reading at pin 101 reduces by not
more than 0.2dB.
Increase input-gain control (27) for a reading of +1dBu at pin 101 and switch in the
limiter (17). Turn the threshold control until the reading at pin 101 is reduced to 0dBu
- at which point the limiter LED (22) should illuminate.
This is the setting requested by customers, leaving 18dB before clipping within the
channel. We believe that this setting is over-cautious and unfortunately destroys input
headroom which the limiter is actually intended to protect.
The range on the threshold preset is -5dBu (ccw) to +15dBu (cw). If set at +15dBu,
the limiter and overload LEDs would operate together. For optimum use of the limiter,
we suggest it be set at +12dBu, ie 6dB before clipping.
(The DC voltages on IC10 should be approximately -2.6v at pin 10 and -2.0v at pin 12,
ie a difference of 0.6v)