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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
coder inputs disconnected from audio processor. Then,
it must be necessary to install a new flat cable
connector set, that
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.
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.
ORION 462 MKII
stereo
Calibrate
channel
SOLIDYNE
h) Verify channel separation at the 20 Hz –
15.000 Hz range This must be better than 60
dB (65 dB typical).
5.5
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)
5.6
Audio Distortion measurements
Connect a good distortion measurement set like
System ONE 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
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:
100
=
×
Distorsión
H
1
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 under 0,003
% at 1 KHz.
output
of
the
THD
(
+
+
+
Κ
2
2
2
H
2
H
3
H
4
27
)
1
2
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