Marantz PMD520 manual Auto Bias & EQ System, System Operation Description

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.

Figure 1

Level	64 Step
	100msec
	Time

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.

Figure 2

levelOutput	Peak point		-5dB (NORMAL)
	BIAS point	BIAS level

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.

Figure 3

											C
(dB)	30
Gain
	20						A		B
												English
	10
	0
	-10				400Hz			3kHz		12.5kHz
	20	30	50	100	200 300	500	1k	2k 3k	5k	10k	20k	Frequency (Hz)

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.

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