Marantz 3-Head Double Cassette Deck PMD520 - Manual (Page 16)

15
English
English
AUTO BIAS & EQ SYSTEM
System Operation Description
This system sets the recording bias, recording gain, medium-
frequency gain, high-frequency gain and high-frequency peak
automatically so that the characteristics of the tape in use can
be exhibited fully.
D/A output from the microcomputer
As shown in Figure 1, the microcomputer adjusts each of the
bias, gain, medium-frequency gain, high-frequency gain and
high-frequency peak levels to one of 64 steps every 100 msec.
by using a 6-bit digital-to-analog converter.
Bias setting
The recording bias is set as shown below according to the char-
acteristics of the record head.
Set frequency: 6.3 kHz
Set bias point: As shown in Figure 2, the bias point is set so that
the output level is lower by -5 dB (Normal or High tape) or -2.5
dB (Metal tape) than the peak point. This setting is the optimum
point for utilizing the tape performance (MOL, third-order dis-
tortion) available from the record head in use.
Recording gain setting
An internal oscillator outputs a 400 Hz signal in the range of ±5
dB. This signal is recorded and played to adjust the recording
gain so that the output level becomes the standard level. This
adjustment is not performed at a specific frequency but varies
only the gain, regardless of the frequency, as shown by A in
Figure 3.
Medium-frequency gain
The internal oscillator outputs a 3 kHz signal in the range of ±4
dB. This signal is recorded and played to adjust the recording
gain at around 3 kHz so that the playback output becomes the
standard level as shown by B in Figure 3.
High-frequency gain
The internal oscillator outputs a 12.5 kHz signal in the range of
±3 dB. This signal is recorded and played to adjust the record-
ing gain at around 12.5 kHz so that the playback output be-
comes the standard level as shown by C in Figure 3.
The following conditions should be met so that the adjustment
can be started.
¡ A cassette tape with unbroken erasure protect tabs should
be loaded.
¡ The mechanism should be in stop mode.
¡ The tape speed should be set to normal. (The adjustment is
not available with the high speed.)
To start the adjustment, press the REC MUTE while pressing
the REC button.
Ab will appear on the display followed by a number that will
count down until the adjustment is complete.
Pressing the
STOP button during adjustment cancels it.
If an Error occurs please refer to page 13.
After the adjustment, the tape is rewind automatically to the point
where the adjustment was started.
The AUTO BIAS indicator lights up after the adjustment.
– The AUTO BIAS and EQ system uses 3 memory areas for
the normal, High and Metal tapes.
– The BIAS RESET buttons will return to the standard charac-
teristics for the normal, High and Metal tapes.
– The data obtained by the adjustment is held in the EEPROM
even after the unit is turned off.
– In case the adjustment fails, "Err" (error) is displayed on the
counter for 15 seconds, then the factory-set data is recalled.
– In case the adjustment is canceled in the middle or the unit
is turned off during the adjustment, all data adjusted until
then are invalidated.
– The tape is not rewound in case an adjustment error occurs
or the adjustment is canceled in the middle.
– When the data obtained by the adjustment is held in memory
and the BIAS RESET indicator is lit, the adjusted setting is
recalled at the moment a tape is loaded.
– To use the factory-set data, press the BIAS RESET button
so that the indicator is off.
– Performing this adjustment overwrites the previously stored
adjustment data.
Figure 1
Level
Time
64 Step
100msec
Output level
BIAS point BIAS level
Peak point
-5dB (NORMAL)
Figure 2
12.5kHz 3kHz 400Hz
30
Gain (dB)
20
10
0
-10
20 30 50 100 200
A
300 500 1k 2k 3k 5k 10k 20k Frequency (Hz)
B
C
Figure 3