TDA7404

Description of functionality

21/35

4.9

External AC - coupling

TDA7404 has external AC coupling terminals which can be selected one of two positions

behind the mixing stage or bass filter.

Figure 16.

External AC coupling

The external AC coupling is selected in position of four switches controlled by the lower 2bit

in the Others selection (seeTable 6).

4.10

Speaker attenuator

Due to practical aspects the steps in the speaker-attenuator are not linear over the full

range. At attenuations more than 24 dB the steps increase from 1.5 dB to 10 dB (please see

data byte specification).

4.11

Subwoofer attenuator

The Subwoofer output is a single ended stereo output. The attenuator is exactly the same

like the other speakers.

Table 6.

Others selection

D1

D0

Switch position

X

0

SW3 = ON, SW4 = ON (selected internal pass), SW1 = b, SW2 = open

0

1

SW3 = OFF, SW4 = ON, SW1 = a, SW2 = a

1

1

SW3 = ON, SW4 = OFF, SW1 = b, SW2 = b

b

a

b

a

SW2

SW1

SOUND

EF FECTS

Volu m e & Filter

ACC select or

Input

Speaker

ACOUT

ACIN

Mixing

St age

SW3

SW4