Technics RS-273US - Page 12

MEASUREMENT & ADJUSTMENT
REMARKS
Adjustment of the overall frequency response by using CrO2
tap
1.
2.
ee
4.
e
Dolby NR switch is set to OUT position.
Tape selector is set to CrO2 position:
Never adjust the bias current.
ust uSe technics CrO2 tape (C-RF).
Adjustment method
Wh
en the frequency response is flat in the middle-frequency
range and makes a sharp rise or drop in the high-frequency
range as shown in fig. 25, adjust by turning the VR1103
(L-CH), VR1104 (R-CH) for CrOz recording equalization.
* Location of VR1103 and
VR1104 are shown in
fig. 26.
Overall S/N Ratio
Equipment:
* VTVM
* AF Oscillator
* ATT
* Oscilloscope
* Test Tape
(Reference Blank Tape)
«C-RA
. Test equipment connection is shown in fig. 18.
2. Supply 1 kHz signal (— 14 dB) to LINE IN and adjust record
level contro! so that VU meter indicates 0 VU.
. Further adjusting ATT. increase input signal by 4d8 (Line
output level=0.5 V (—6 dB) 4dB=0.8V (—2dB)).
. Make recording.
. Make another recording without supplying signal (discon-
nect input plug from LINE IN jack).
. Rewind to recorded part and playback.
. Measure output signal level and no signal level! (noise),
and determine the ratio in decibels (dB).
. The value is difference between ‘Playback S/N and Overall
NO
1
S/N", but for decibel calculation refer to “Playback S/N
Measurement” described on page 8.
Standard Value: Greater than 49dB |
TE: NAB FILTER
lf there may occur a connection loss with the filter, use
care about the method of reading the output level. For
instance, when the !oss is 6dB the value measured actu-
ally is —12dB, whereas the specified output is —6dB.
As for measurement of S’N ratio, both signal and noise
are 6dB smaller, but the S‘N ratio remains unchanged.
. With the filter built-in an amplifier, there occurs no such
an insertion loss in (1) above, but may occur hum noise
for which care should be taken.
Dolby NR Circuit
Equipment:
* VTVM
* AF Oscillator
* ATT
* Oscilloscope
* Record/Playback Mode
* Erase the tape with a
bulk tape eraser.
. Place unit into record mode, set the Dolby NR switch to
OUT position and supply 5kHz signal to LINE IN jack to
obtain —33dB at TP5 (L-CH), TP6 (R-CH).
. Confirm that the value at IN position is 8dB greater than
the value at OUT position of Dolby NR switch.
. When it is not in condition above, adjust as follows
_ Fully turn VR401, VR402, VR403, and VR404 in direction
opposite to arrow indication.
. Set the Dolby NR switch to IN position.
. At this time adjust VR403 (L-CH), VR404 (R-CH) so that
the reading of VTVM become
the value in step (1) above).
-~23dB (10dB greater than
. Adjusting VR401 (L-CH), VR402 (R-CH), make the reading
of VTVM becomes —25dB (2d8 smaller than the value
obtained through the adjustment in step (6) above).
' * Record Mode
* Record Level Contro!
we MAX
3% Doiby is the trade mark of Dolby Laboratories Inc.