Akai 1731 W Service Manual

Page 2

STEREO TAPE RECORDER

MODEL 1731W

ALSO APPLICABLE TO MODEL 1731L STEREO TAPE
RECORDER AND 1731 D STEREO TAPE DECK

SECTION 1 SERVICE MANUAL ....................... 2
SECTION 2 PARTS LIST ........................... 19
SECTION 3 SCHEMATIC DIAGRAM .................. 44

Page 6

5. TOTAL HARMONIC DISTORTION

FACTOR
Audio , l731W
Frequency A.T.T. _ PM
Oscillator - _ input
Line output

l |

Distortio n
Meter

Fig. 5

Connect the measuring instruments as shown in
Fig. 5 and record a 1,000 Hz sine wave signal at
0 VU. Playback the resultant signal and measure
the overall distortion factor. Measure the noise level
of the tape recorder without the tape. Connect the
Audio Frequency Oscillator directly to the distortion
meter for measurnent of the distortion factor of the
oscillator. The required distortion factor can be
obtained from the results of the above measmement
by the following formula:

do=d'did2

Where, do - Requned distortion factor
d # Overall distortion factor
d1 - Noise level
d2 - Distortion factor of the oscillator

NOTE: When measuring the distorion factor, new
tape should be used.

6. CROSS TALK
(Cross talk between the tracks)

:> TAPE
DIRECTION

Fig. 6

As shown in Fig. 6, first record a 1,000 Hz sine
wave signal on Track No. 3 at +3 VU level. Next,
record under a non-input condition. Then, play-
back the tape on Tracks No. 3 and 4 through the
B.P.F. (band pass filter sensitivity. . . 1:1) and obtain
a ratio between the two from the following formula:

_ 50
C - 20 log E2 _ E1 (dB)
Where, C 7 Desired cross talk ratio (dB)
130- 1,000 Hz signal output level _
E2- 1,000 Hz cross talk level W
E] - Non-input signal recorded level

7. ERASE RATIO

As shown in Fig. 4, connect a High Sensitivity
V.T.V.M. to the Line Output of the recorder.
Playback a virgin tape and take a V.T.V.M. reading
of the output level. Next, record a 1,000 Hz sine
wave signal at +3 dB, then playback this recorded
signal and take a V.T.V.M. reading of the output
level. Next, using this pre-recorded tape, record
under a non-input condition and take a reading of the
noise level output of the erased signal and obtain a
ratio between the two from the following formula:

_ E
Er - 20 lo 9 dB
g E A El ( )
Where, Er - Desired erase ratio (dB)
Ea - 1,000 Hz signal omput level
E2 - Non-input signal recorded level
E, - Virgin tape noise output level

8. POWER OUTPUT

dummy
1731w 8-9 High
Speaker % Sensitivity
output V.T.VM.

Fig. 7

As shown in Fig. 7, connect an 80 dummy load
resistor to the speaker output of the recorder and
connect this terminal to a High Sensitivity V.T.V.M.
Playback a 250 Hz 0 VU pie-recorded test tape
and take a V.T.V.M. reading of the output level.
The resultant output can be obtained from the
results of the above measurement by using the
following formula:

=E
P R (W)

Where, P - Desired power output (watts)
E - Measured voltage (RM.S.)
R- 89