394

Audio ICs

BA3528AFP / BA3529AFP

(4)

Mute amplifier output

To switch the mute amplifier on and off, switch the

constant-current supply for the mute amplifier off and on

by switching the voltage on pin 1 (Pre-mute SW) high or

low. When the mute is switched on, the mute amplifier

output goes open circuit and the output voltage is unsta-

ble resulting in the generation of an audible “pop” sound.

To prevent this, bias pin 22 through the volume control as

shown in Fig. 13.

In applications that use a directly connected output cou-

pling capacitor, connect a resister as shown in the circuit

diagram in Fig. 14 to reduce the pre-mute switching noise

described in (3) above.

(5)

Preventing oscillation

Connect a capacitor of approximately 1000pF between

the preamplifier input and pin 22 to prevent oscillation,

and as a countermeasure against strong electric fields.

This capacitor can also be used for treble-region com-

pensation. In this case, decide on a value for it based on

the relationship with the impedance of the magnetic head

(see Fig. 15).

When countermeasures against strong electric fields for

the power amplifiers are required, connect bypass ca-

pacitors between each input pin and pin 22, and connect

choke coils in series with the output pins and the head-

phones. The component values should be about 330pF

for the bypass capacitors, and the 10

µH for the choke

coils so that they do not effect the audible frequency

range.

Another effective measure is to connect a bypass capaci-

tor of about 1000pF in parallel with the filter capacitor be-

tween pin 22 and ground (pin 21). Refer to the circuit dia-

gram in Fig. 16.