mind that the common mode rejection isn’t applicable
for this input.
5.1.4 Balanced Outputs
All the measurements must be carried out in the same
way that the unbalanced outputs, but disconnecting of
GND the instrumental used and connect it between
the two balanced terminals.
Another possibility is to measure all in unbalanced
mode (only one pin),
adding 6dB to the results.
5.1.5 Unbalanced Outputs
Connect the audio generator to line left input; adjusted
at +4dBm/1KHz. Connect an audio level meter and
the oscilloscope with a charge of 600 ohms, to the
SEND left output (pin 9 of the master connector).
In the channel under test, select LIN and SEND. The
other buttons must be out.
Enable the channel by pressing the AIR button. Open
the main fader up to -10 dB. Change the generator
level until reach the limit of clipping. Verify that the os-
cilloscope shows a greater or equal level +18 dBm.
Repeat for the right channel (terminal 10 of the Master
connector). In the previous condition, repeat the out-
put measurement for mono PGM output.
5.1.6 Gain
Connect the microphone input to an audio generator.
Connect the audio level meter and the oscilloscope to
the output. Charge this output with 600 ohms.
Adjust the generator to 1 kHz / -80 dBm. Select MIC
and PGM in the channel. Enable the module by press-
ing the AIR button. Take the main fader and the gain
control to the maximum position. The difference be-
tween the obtained output level and -80dB is the gain
of the console.
5.1.7 Frequency Response
Connect the generator to a microphone input. Con-
nect an audio level meter and an oscilloscope to the
output. Load it with 600 ohms. Change the audio gen-
erator to 1 kHz / -50 dBm. Select MIC and PGM in the
channel. Enable the module pressing the AIR button.
Move the main fader to the value -10 dB. Change the
gain of the module or the generator output until ob-
t4dBm at the output. Change the frequency
between 20 and 20.000 Hz and verify the frequency
response.
5.1.8 Phase
Staying the conditions of the previous item, connect
the generator to both microphone inputs (right and
left). Connect a digital phase meter to the channels
left and right of the program output. Load each chan-
nel with 600 ohms. Change the generator’s frequency
to measure the phase. The variation will be smaller
than 2 degree between 50 Hz -15 KHz.
5.1.9 Stereo Tracking
Maintain the conditions of the previous item. Change
the generator frequency to 1 kHz. Take the main fader
to the maximum. Adjust the Pan-Pot to obtain the
same level in both channels (L & R) of PGM output.
This level will be in order of +10 dBm. Now, move the
fader between 0 and -30 dB and measure the differ-
ence among the levels of both program outputs. This
difference will be below +/- 0.2 dB
5.1.10 Harmonic Distortion (THD)
Connect the audio generator at 1 KHz / + 4 dBm, to a
left line input. Connect a Harmonic Distortion meter
and the oscilloscope to the left program output. Load
this output with 600 Ohms. Then, select LIN and PGM
in this channel. The other switches should be out.
Enable the module by pressing the AIR button. Take
the fader to the maximum level (0 dB). Then, change
the preset line level until obt4 dBm on the left
output. Measure now the total harmonic distortion.
Change the frequency between 30 and 15,000 Hz and
to check if the distortion is below the specification. Re-
peat for right channel.
Reduce now the level from the generator to -50 dBm
and connect it to the microphone input. Take the fader
to 0 dB position. Select MIC; change the level from the
MIC preset gain, until obt 4 dBm at the output
and to proceed like in the previous item.
It is necessary to keep in mind so that this measurement has validity,
the following conditions must be verified:
1.
The measurement chain must have a distortion smaller than
0,002%.
2.
The distortion components, just as they are seen at the oscillo-
scope screen, connected to the output of the THD meter, must
be clearly distinguished from the residual noise and buzz.
5.1.11
Equivalent Input Noise
Connect the audio generator to a microphone input.
Load it with 600 ohms. Connect to PGM output an au-
dio level meter with A-weighted filter. Change the gen-
erator output to 1KHz / -45 dBm. Select MIC and PGM
in the channel under test. Enable the module by
pressing AIR. Set the main fader to -10 dB. Change
the gain control until obt4 dBm at the console
output (this is the reference level: REF).
Now, replace the audio generator by a resistor of 150
ohms placed inside the D-25 MIC input connector.
Measure the residual noise in the audio level meter
with “A-weighting” filter. We will denominate it
Vn(dBm). Verify in the oscilloscope that there is not
any buzz; only random noise signal. In order to elimi-
nate buzz, reconnect the grounds of the measurement
instruments so that the buzz disappears. The level of
equivalent input noise will be:
EIN = Vgen + Vn-REF; that is to say:
EIN (dBm) = 49 + Vn (dBm)
Waited value: 133 dBm
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Broadcast mixing consoles - 2600 series
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