CHECK ADJUSTEMENTS

 

1. PREPARATIONS

 

1-1 Preparatory Settings

· Unless otherwise specified, the volumes and switches on the front panel are to be set as follows:

INPUT VOL...............MAX

INPUT LEVEL SW...........+ 4 dB

OUTPUT LEVEL SW.........+ 4 dB

· Leave the slide switches SW103, SW104 ynd SW105 within the AD circuit set to the TEST position.

· The load of the OUTPUT L and R connectors are to each be serially connected to a load resistors (30012 t 3000).

 

1-2 Measuring Instruments

· Prepare the following: AF signal generator, electronic voltmeter, distortion meter, oscilloscope, load resistors on.

· For the distortion measurement, a low-pass filter with cut-off frequency of 80kHz and 6dB/OCT must be used.

· For the noise level measurement, a low-pass filter with the cut-off frequency of 12.7kHz and,.-6dBlOGT must be used.

· The output impedance of the AF signal generator must be less than 6000.

· The input impedance of the measuring instruments must be over 1 M OHM

 

2. INSPECTION

 

2-1 Gain

 

2-1-1 Total gain {Reverberation signal}

When the input signals below are applied to the INPUT connector, switching of the LEVEL switch. enables the. output signals of the table below to be obtained at the OUTPUT L and R connectors. (After inspection, set the LEVEL switch to +4dS.)

 

 

INPUT LEVEL

 

OUTPUT LEVEL

 

INPUT

 

OUTPUT

 

 

+4

 

+4

 

5 dBm

 

+4t 1dBm

 

 

+ 4

 

20

 

20

 

+4

 

6 dBm 30 dBm

 

20 t 3 d8m +4 t 3dBm

 

 

20

 

20

 

30 d8m

 

20 t 3dBm

2-1-2 Bypass circuit

When the BYPASS switch is switched ON accordding to the conditions of Table 2-1-1, output signals of +4 -+2 dBm are obtained at the L and R OUTPUT connectors. (After inspection, set the BYPASS switch to OFF.)

 

2-2 Frequency Characteristics

When an input signal of approximately -10 dBm is applied from the INPUT connector in the accordding to the status of Table 2-1-1 and the conditions stated in section 2-1-2, the frequency characteristics of the OUTPUT L and R connectors are within the range listed in the table below. The reference frequency used is 1kHz.

 

 

20Hz 11kHz

 

12kHz

 

20k Hz

 

 

2-1-1

 

+1- 2

 

+1- 5

 

 

2-1-2

 

+ 1 2

 

2-3 Distortion Factor

 

 

+1 2

 

+1 3

 

(dB)

 

2-3-1 Maximum output distortion

With the conditions set according to Table 2-1-1, the distortion factor should be less than 0.1%.

 

2-3-2 Distortion factor of distortionless output

When a 1kHz input signal is applied to the INPUT connector, the distortion factor just before the clipping of the output waveforms at the L and R OUTPUT connectors should be less than 0.02% (OUTPUT waveforms can be observed by utilizing the monitor output of the clis-tortion metr or connect) an oscilloscope to the output load.

 

2-4 Maximum Output

When a 1kHz input signal is applied to the INPUT connector according to the conditions of section 1-1, tlirt. maximum level of the output signal at the L and R OUTPUT connectors should be +18 dBm with a distortion factor of less than 1%.

 

2-5 Meter Sensitivity

When a 1kHz input signal is applied to the INPUT connector according to the conditions of section 1-1, and the input signal has been adjusted so that an output signal of +10 i 4 dBm can be obtained at the L and R OUTPUT connectors, the '0' level of the level meter is illuminated.

At this point, all LED indicators below the '0' level are illuminated.

 

2-6 Muting Circuit

After the POWER switch iS turned ON, muting is effective for three to four seconds, and no output signals are generated. After this time delay output signals can be obtained at each OUTPUT connector.

When the POWER switch is turned OFF, muting becomes effective so that no clicking noise is generated.

 

3. ADJUSTMENT

 

3-1 'A/D Gain Adjustment

Apply an input signal of <8.5 dBm at 1kHz to the INPUT connector and adjust VR 101 so that the output signal is clipping slightly at the L OUTPUT connector. Adjust VR 103 so that the clipping signal is vertically symmetrical. (Observe the distortion waveforms by utilizing the monitor output of the distortion meter or connect the oscilloscope to the output load.)

Afterwards, adjust VR 101 until the distortion wave-forms of the L OUTPUT connector for minimum distortion.

 

3-2 D/A Gain Adjustment

With the same input conditions as stated in section 3-1, adjust VR 102 so that theoutput signal of the L OUTPUT connector becomes +1B.5 ~ 0.2 dBm.

 

3-3 Noise Level Adjustment

After performing spectons 2-1 through 2-6, set the slide switches SW102, 104, and 105 on the AD circuit board to the NORMAL position and set the BALANCE level to '0' (DIRECT).

When the INPUT is opened, the noise levels of the L and R OUTPUT connectors should be less than -65dBm. If noise levels are not within rated levels, adjust VR 103 on the AD circuit board so that the noise levels are within rated values.

Note that this adjustment must be performed approximately five seconds after the POWER switch is switched ON. At this point, perform the Offset Check using Test Program 5, after the level clicking noise or offset has been minimized, and verify that the noise meets the previously stated specification.