Wohler ALARM-24 Series User Manual download pdf (Page 14)

ALM26 Series User Manual P/N 821644 Rev-A

Rear Panel Features

Section 2: Operation

(Continued)

Analog Audio Inputs

(ALM26-nnA Only)

The Analog units have balanced (>10K Ω impedance) inputs terminated in 6-pin "mini" Phoenix connectors. There are two

separate analog signals; one signal to the left three pins (CH A) and the second signal to the right three pins (CH B). There are two

input connectors per input section (4 channels). Channel numbers are displayed on a label to the side of each connector and

correspond to the channel numbers above the associated bargraph meters on the front panel. Pin-out information is silk-screened on

the rear panel directly below each connector.

Analog Line Level, Reference Level, and Display Mode DIP Switch

(ALM26-nnA Only)

This DIP switch sets the Line Level Calibration, Reference Level, and PPM/VU Display Mode. Each DIP switch module

affects only the four channels within the section in which it is located. See the descriptions and diagram below for setting

information.

Line Level (Auto) Calibration:

The unit is calibrated at the factory. To recalibrate:

1) Turn on the power.

2) Apply the desired reference level (nominal 0) signal to all four channels.

3) Make sure the Reference Level DIP sections (2 and 3) are set to the nearest level of the input signal being applied for

calibration (i.e., 0, +4, +6 or +8). The user should make sure that the signal applied to all four channels is within +/- 4 dB of the

reference level selected by DIP switch sections 2 and 3.

4) Place DIP section 1 in the DOWN position.

5) Wait 10 seconds. The unit will remove the previous calibration and the new calibration will be applied.

6) Place DIP section 1 in the UP position and return unit to service.

7) Only ONE auto-calibration attempt may be made for each cycling of AC power to the unit. Once the Line Level Calibration

DIP switch has been placed in the CAL position, it is necessary to cycle the power before that DIP switch will be functional again,

EVEN if a calibration attempt was unsuccessful.

If one wishes to calibrate again, turn off the power to the unit and repeat steps 1 through 6.

Reference Level:

DIP switch sections 2 and 3 determine the Reference Level, which adjusts the level of the input signal and the resultant level

displayed on the LED bargraphs. Factory setting is +4 dB. See diagram below for settings.

Bargraph Display Mode:

DIP switch sections 4 and 5 determine how peak levels are displayed for the four associated meters on the front panel.

There are four possible settings; VU Bargraph Only, VU Bargraph with PPM Floating Segment, PPM Bargraph

Only, and PPM Bargraph with PPM Floating Segment. The factory default setting is VU Bargraph with PPM Floating

Segment. See diagam below for settings. See the ALM26 Internal Settings - Address, Peak Hold, PPM Characteristics

diagram on page 23 for how to set the Peak Hold and PPM Ballistics characteristics.

NOTE: For more accurate indication of signal levels, analog meters are tuned to effect a “rounding” function which occur BETWEEN the

thresholds of any two bargraph segments. This means the level meter zero LED segment will turn on at one-half the smallest spacing between

LED segments (mid-scale resolution) before that segment's scale indication. This "rounding offset" is 0.5 dB for the Analog (extended VU),

Digital, Nordic, BBC, and DIN scales. It is 0.25 dB for the VU scale. For example, using the Analog (extended VU) scale, a meter

calibrated for a +4 dBu nominal level will actually turn the zero LED segment of the level meter on at 3.5 dBu and all segments will turn on at

0.5 dBu before that segment's silk-screened scale indication.

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Wohler ALARM-24 Series User Manual Page 14

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