1

2

7

32

667

Audio ICs

BA6820F / BA6822S / BA6822F

FAttached components

for the square-root compression amplifier. The rectified

voltage output from pins 2 and 4 is attenuated by 1.5dB

at the frequency determined by the following formula (re-

fer to the data for the relationship between the pin 2 and

4 DC voltage frequency characteristics and the LED

lighting level).

fC =

When the LEDs light due to low-frequency mechanical

to cut the cut the low-frequency frequency characteris-

tic.

sitivity and L / R balance adjustment (refer to item 2 of

Circuit operation).

These resistors set the attack and release times (refer

to item 6 of the Circuit operation).

Ω carbon-film resistor.

This resistor sets the oscillator frequency (refer to the

Operation notes).

used as a ripple filter. The positive lead should be con-

close to the junction of pins 10 and 11.

so that sufficient base current flows.

set the LED current. Four LEDs are connected to each

resistor, but as the LEDs light sequentially, only the cur-

rent for one LED flows in a resistor.

R8

X13 =

FCircuit operation

(1)

Function

There are 12 LEDs each for the left and right channels,

and these are divided into 4 groups of six. A dynamic-

drive technique is used to drive the LEDs in order, and

provide 12 display points for each channel. A 12-point

VU-scale bar display is produced over the display range

*38dB to +10dB. The top eight points have a peak hold

function which may be cancelled if required (there is no

peak hold function for DC mode).

Independent AC (two channels) and DC (one channel)

inputs are provided, and a control input pin is used to

switch between them.

In DC mode, only channel 2 operates.

A power-on mute circuit is provided, so no measures are

required to prevent erroneous lighting of the LEDs when

power is applied.

The attack and release times for the display can be set

using external components.

(2)

Input block (pins 1, 3 and 5)

Pins 1 and 3 are the AC inputs, and pin 5 is the DC input.

Pin 6 is used to switch between AC and DC input. When

the pin 6 input is “H”, AC input is selected (pins 1 and 3),

and when it is “L”, DC input (pin 5) is selected. Therefore,

if pins 1 and 3 are used for audio input, and pin 5 as the

input for signal meter output (DC) from a tuner, the switch

input (pin 6) can be used to make LED display do two

jobs.

Pins 1 and 3 have low input impedance, so we recom-

5k

Ω to 100kΩ) in series with the inputs to adjust the bal-

ance between ch1 and ch2 and set the levels.