Solidyne 462dsp, User Manual

Page: 36 / 38

Page 36
SOLIDYNE 462
dsp - broadcast digital processor
e)
Change the phase calibration jumper to NORMAL
mode (“N” position).
7.2.4 CHANNEL SEPARATION
Due to the high channel separation of the Solidyne
SC-100, the only way to recalibrate to original
specifications is to use as reference a good
measurement set like the BELAR (USA) model
FMS-2.
If you do not have an excellent measurement set,
please do not intend this calibration. Anyway the
Factory Calibration of our stereo coder, do not
change with the years.
Note 1:
Previous to this adjustment, the Pilot Phase (item #
2) must be adjusted.
Note 2:
This calibration must be done with stereo coder
inputs disconnected from audio processor. Then, it must be
necessary to install a new flat cable connector set, which
avoids connection with audio processor and allows direct
connection of the audio generator to
JS1
and
JS3
(JS
connector).
a)
Verify that the input stage bias is correct. Use a DC
millivoltimeter to check that voltage difference
between TP2 (R222) and TP3 (R233) is less than
0,1 mV. If not, correct it using P1.
b)
Connect the BELAR measurement set to the MPX
output connector.
c)
Check the PHASE mode of the Belar. You must get
at least – 65 dB rejection at 19 KHz pilot tone. If not,
please make the Belar calibration procedure of
PHASE (see Belar manual).
d)
Connect a sine wave generator at 400 Hz, 1V RMS
to the Left Input (pin
JS1
). Leave disconnected the
right input
S3
.
e)
Measure channel separation at the Belar. Right
channel will be under 70 dB (typical is 75 dB).
Correct the phase control of the Belar to improve
this figure. Calibrate channel separation to the
minimum Right level, using
C1
trimmer at the low
pass filter of SC100. More than 70 dB rejection is a
correct figure. If not, make the complete procedure
of channel separation calibration of the Belar set
(see Belar manual).
f)
Now, connect the sine wave generator, at the same
frequency and level, to the Right Channel (pin
JS3
).
g)
Measure at the Belar the residual level of the Left
channel. Calibrate channel separation to the
minimum Left level, using
P2
control. More than 70
dB rejection is a correct figure.
h)
Verify channel separation at the 20 Hz – 15.000 Hz
range. This must be better than 60 dB (65 dB
typical).
7.2.5 MEASUREMENT OF RESIDUAL NOISE
Disconnect
S1
and
S3
from the Audio Processor.
Use a good Audio Voltmeter with A weighted filter
connected at the Left and Right audio outputs of
the BELAR modulation monitor. Use as reference
4 Vpp sine wave. Values better than 92 dBA must
be measured (94 dBA is typical value)
7.2.6 AUDIO DISTORTION MEASUREMENTS
Connect a good distortion measurement set like
System ONE, Agilent 8903B or Sound Tech ST
1710A to the Left & Right audio outputs of the
BELAR set. Values under 0,01 % must be
measured at 1 kHz.
Since Belar has it distortion floor at 0,01%, in
order to measure the real distortion of SC100
stereo coder, is recommended to use a procedure
not based on modulation monitors. Proceed this
way:
a)
Connect to ground Test Point
TP1
in order to cancel
19 KHz Pilot
b)
Then, connect a very low distortion audio generator
at both inputs
S1
&
S3
. This will cancel 38 Khz
subcarrier. Connect a good THD distortion
measurement set at the MPX output of stereo coder.
Adjust to minimum value the THD meter.
c)
Use the monitor output of the THD measurement set
to analyze the distortion products in order to
separate 38 KHz residual and noise from the true
distortion components. Use a Tektronix 5L4 N
analyzer, or TiePie FFT HS3 probe, or SoundTech
Lab software, etc. Identify the harmonics of 1 KHz
and calculate:
( )
2
1
2 2 2
4 3 2
1
100
Κ + + + × = H H H
H
Distorsión
H1
= Level of fundamental tone.
Hn
= Level of harmonics (reduced by the gain set
of the THD meter).
d)
Verify that the distortion level is lower than 0,003 %
at 1 KHz.