Measuring Method - Akai 4000DS Service Manual

II. MEASURING METHOD
1. TAPE SPEED DEVIATION
1
Frequency
4000DS
counter
Line output
input
Fig. 1
As shown in Figure 1, connect a Frequency Counter
to the Line Output of Model 4000DS.
Take a frequency counter reading at the beginning,
middle, and end of tape winding during playback.
The maximum value of these respective readings will
represent tape speed deviation.
2. WOW AND FLUTTER
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4000DS
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I inner
Meter input
Line output
Fig. 2
Method A
As shown in Fig. 2, connect the Line Output of
Model 4000DS to the Input of a Wow and Flutter
Meter. Use a 3,000 Hz pre-recorded test tape and take
a wow and flutter meter reading at the beginning,
middle, and end of tape winding. The maximum value
of these respective readings will represent the wow
and flutter.
Method B
Supply a 3,000 Hz sine wave signal from an Audio
Frequency Oscillator and make a recording on a
blank tape at the beginning, middle, and end of tape
winding. Rewind and playback tape. Measure wow
and flutter with a Wow and Flutter Meter. (The wow
and flutter value of Method B will be close to twice
that of Method A.)
3. FREQUENCY RESPONSE
Audio
Frequency ollt
Oscillator put
f. 4000DS
Line
input Line
output
ATT.
<
High Sensitivity
V.T.V.M.
Fig. 3
For measuring frequency response, connect instru¬
ments as shown in Fig. 3 and proceed as follows:
1) Supply a 1.000 Hz sine wave to the Line Input of
Model 4000DS from an Audio Frequency Oscil¬
lator through an Attenuator. Set recorder to re¬
cording mode and turn recording level volume
control to maximum. Adjust Attenuator to obtain
a +4 dB V.T.V.M. reading.
2) Under conditions described in I) above, re-adjust
Attenuator so that the Line Output is-16 dB, and
record 40 to 20,000 Hz spot frequencies.
3) Rewind tape and playback from the beginning.
Take V.T.V.M. spot frequency readings and plot
values on a graph.
NOTE: When measuring frequency response, new
tape should be used.
4. SIGNAL TO NOISE RATIO
4000DS
High Sensitivity
Line output
V.T.V.M.
Fig. 4
As shown in Fig. 4, connect a High Sensitivity
V.T.V.M. to the Line output of Model 4000DS.
Playback a 250 Hz "O" VU pre-recorded test tape
and measure the output. Then remove the tape and
measure the noise level under the same condition.
Convert each of the measured values into decibels.