Measuring Methods - Akai X-V Service Manual

Il. MEASURING METHOD
1. TAPE SPEED DEVIATION
1. Method involving use of pre-recorded tape.
Playback on the tape recorder to be tested a tape
pre-recorded at 1,000 Hz ± 0.1% for measuring tape
speed deviation. Connect the appropriate output to a
frequency counter me ter in arder to measure the tape
speed deviation from the deviation of the
~easured
frequency.
2. Method involving use of timing tape ( designed for
tape speed measurement).
This method utilizes a timing tape marked at intervals
of 7-1/2". The running time of the tape over 60
marked section is measured in arder to calculate the
deviation of the tape speed. In applying this method,
however, it should be born in mind that should the
timing tape stretch or contract, measurement error is
inevitable, so that it is necessary to measure the total
length of the tape in advance.
2. WOW AND FLUTTER
Playback the 3,000 Hz pre-recorded tape whose wow
and flutter level is guaranteed to be smaller than 0.07%
for measurement by means of a wow meter. It is also
possible for a 3,000 Hz sine wave to be recorded and
played for measurement by means of the wow me ter. In
this case, however, the wow meter indicates a value as
twice the value given in the specification on the first
page.
3. SIGNAL TO NOISE RATIO
X-V
Line output
V.T.V.M.
Set the speed selector Switch on "7-1/2" ips position
and playback a tape containing a 1,000 Hz sine wave
recorded at "0" VU level on a standard recorder.
Connect a V.T.V.M. to the line output jack of the
recorder and measure its output.
Then remove the tape and measure the noise level under
the same condition. Convert each of the measured values
into decibels.
4. TOTAL HARMONIC DISTORTION
FACTOR
1 Kc/s
Audio Distortion
-
-
X-V
- -
Oscilla tor me ter
Connect the measuring instrument as shawn above, and
record the 1,000 Hz sine wave at "0" VU. Playback the
resultant signal and measure the overall distortion factor.
Measure the noise level of the tape recorder with the
tape removed ; connect the audio oscillator directly to
the distortion meter for measurement of the distortion
factor of the oscilla tor.
The required distortion factor may be obtained from the
results of the above measurement by the following
formula.
do=d-d1-d2
where, d
0
=Requred
d=Overall distortion factor
d1 =Noise level
d2 =Distortion factor of the oscilla tor
(Note : New tape of particularly good quality should be
used for measurement of the distortion factor.)
5. POWER OUTPUT
Playback the tape pre-recorded with a sine wave of
1,000 Hz at "0" VU, and connect an
sn
load resistor to
the output terminais of the tape recorder : measure the
voltage across the resistor with the volume control set to
maximum. Use the following formula to obtain the
required output :
E2
W=R
Where, W .......... Output (watt)
E ........... Output voltage
R ........... Resistor
(Sn)
(Note : The
sn
resistor used in this measurement must
be of high precision).
6. CROSS T ALK
(Cross talk between the tracks)
(TAPE)
CD ( @'
®
®'
Tape direction
@ )
®'
@ w~
CD' Tape dir ection
As shawn in the figure, first record a 1 ,000 Hz sine wave
on track No. 3 at
+
3 VU level. Next, remove the
1,000 Hz input signal and record under a non-input
condition.
Then playback the tape on track No. 3 and No. 1
(reversed condition of tape) through the 1,000 Hz
B.P.F. (Band Pass Filter) and obtain a ratio between the
two from the following formula.
Eo
C = 20 l o g - - (db)
E2-E1
C=Desired cross talk ratio (db)
E
0
= 1,000 Hz signal output level
E 2 = 1,000 Hz cross talk output level
E1 =No-input signal record level