Technics RS-646DS-D - Page 10

Playback frequency
response
Equipment:
* VTVM
* Oscilloscope
* Test tape --- C-FH
Playback gain
Equipment:
*VTVM
* Oscilloscope
* Test tape--- C-FH
MEASUREMENT & ADJUSTMENT
. Test equipment connection is as same as “Head azimuth adjustment” |
but use the test tape (C-FH) instead of head azimuth tape (See fig.
11).
. Place UNIT into playback mode.
. Play frequency response test tape (C-FH).
. Measure output level at 1OkHz, 8kHz, 4kHz, 1kHz, 125Hz and 63Hz
and compare output level with standard frequency 333Hz, at LINE
OUT.
. Make measurement for both channels.
. Make sure that the measured value is within the range specified in the
frequency response chart.
Playback frequency response chart
150Hz 250Hz 333H2 sobez L ski
Fig. 15
. If measured value is not within standard, adjust the following points:
Change the “Connection points’ of the amplifier pattern, and then
adjust the playback frequency response.
@lf the high range (8~10kHz) decreases about —1~ —1.5aB,
short circuit connection points (@) as shown in fig. 7.
@lf the high range (8~10kHz) decreases about —1.5~ —2qB,
also short circuit connection points (B) as shown in fig. 7.
. Test equipment connection is shown in fig. 11.
Play standard recording level portion on test tape (C-FH 333Hz), and
using VTVM measure the output level at LINE OUT jack.
. Make measurement for both channels.
Standard value: 0.42V (—7dB)
Adjustment method
1. If measured value is not standard, adjust VR1 (L-CH), VR2 (R-CH)
(See fig. 28 on page 17).
2. After adjustment, check “Playback frequency response” again.
REMARKS
* Playback mode
; * Playback mode
Playback S/N ratio
Equipment:
* VTVM
* Oscilloscope
* Test tape---C-FH
* Empty cassette
. Test equipment connection is shown in fig. 11.
put level on VTVM.
Refer to "Playback gain adjustment”.
. Place empty cassette (which has been cut) and play again.
. Measure noise level at this time using VTVM, and determine ratio of
this level to test tape output signal voltage (333 Hz).
Standard value: Greater than 43dB |
An example calculation is shown below.
A: Es=playback output signal voltage of test tape (333 Hz)
B: En=playback output noise level
Es=0.42V (—7dB)
En=0.003 V (—50dB)
S/N ratio= Es _ _0.42V — 140
En 0.003 V
20 log:: 140=43dB
S/N ratio = Es(dB) — En(dB) = —7 —(—50) = 43dB
! * Playback mode
. Play standard recording level test tape (C-FH 333Hz) and read out- :