Akai 4000DS Service Manual page 6

5. TOTAL HARMONIC DISTORTION
FACTOR
Fig. 5
Connect the measuring instruments as shown in Fig. 5
and record a 1,000 Hz sine wave signal at "O" 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 Fre¬
quency Oscillator directly to the distortion meter for
measurement of the distortion factor of the oscilla¬
tor. The required distortion factor can be obtained
from the results of the above measurement by the
following formula:
do = d - dj - d2
where, do - Required distortion factor
d - Overall distortion factor
d| - Noise level
d
2
- Distortion factor of the oscillator
NOTE: When measuring the distortion factor, new
tape should be used.
7. ERASE RATIO
As shown in Fig. 4, connect a High Sensitivity
V.T.V.M. to (he Line Output of Model 4000DS.
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 tape 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:
Er = 20 log ^ (dB)
Where, Er - Desired erase ratio (dB)
Ep- 1,000 Hz signal output level
E
2
— Non-input signal recorded level
E| - Virgin tape noise output level
6. CROSS TALK
(Cross talk between the tracks)
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, playback 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:
C = 20 log (dB)
where, C - Desired cross talk ratio (dB)
Eq - 1,000 Hz signal output level
E
2
- 1,000 Hz cross talk level
El - Non-input signal recorded level