Dorrough 10-A, Instruction Manual, Page: 9 / 19

8
Operation
Stereophonic material, in the form of left and right inputs, is fed to the meter
at the terminal strip located in the rear of the meter, as shown in Fig. 1.
Individual gain controls for the left and right inputs are also located on the
rear panel.
These sources feed a 20K balanced bridging amplifier. Unbalanced 10K
bridging input is accomplished by converting the minus (-) input terminal to
chassis ground on the rear terminal strip.
The meter is shipped with each individual input control set for +4 dB as
referenced to “0” on the meter face. Levels as low as -30 dB can be refer-
enced to “0” by changing the value of R-18 from 20K to 100K. Refer to Fig.
15 and Fig. 16 for the location of this component on the Power and Signal
Board.
If your program reference is different than that of +4 dB, simple adjustments
to some other standard can be made by the following the procedure listed in
the Field Alignment section.
Applications
DORROUGH Loudness Monitors can be used in a number of applications, as
shown in Fig. 7 through Fig. 13, including: Telephone/Transmission, AM
Mono Broadcast, Analog/Digital Tape Saturation Monitor, Sum & Difference
Monitor, Stereo Television Broadcast, Disk Mastering, and Sound Reinforce-
ment.
ISOLATION CAPACITORS
LOUDNESS MONITOR
MODEL 40-A
-25
-22
-20
-18
-16
-14 -12
-10 - 8 - 6 - 4 - 2 0
+ 2 + 4
+ 6
+ 8
+10
+12
+14
NORMAL
PEAK
RANGE
NORMAL
RANGE
PERSIS
TENCE
dB
dB
Fig. 7. Telephone and/or Transmission Applications. The DORROUGH
Loudness Monitor ("A" Type or "B" Type) can be utilized to monitor power
line condition or telephone line signal, as shown in the above line drawing.
Make sure that some form of isolation, either transformers or capacitors, is
used in this application.
OPERATION & APPLICATIONS