Audio ICs
BA6820F / BA6822S / BA6822F
FAttached components
S C1 and C2: 1µF input coupling capacitors (electrolytic)
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).
S Q1 to Q4: 2SA854S Transistors for display switching.
If the current for one LED is ILED, the values of IC and PC
for each of Q1 to Q4 when all LEDs are lit are given by:
IC = 6 ILED (for duty cycle of 7/32)
7
PC = 6 ILED Vsat
32
1
fC =
(RIN = input resistance)
Choose transistors that have sufficient margin for IC and
PC.
2π S C1 (RIN)VR1)
When the LEDs light due to low-frequency mechanical
noise or induced hum, reduce the values of C1 and C2
to cut the cut the low-frequency frequency characteris-
tic.
S R4 to R7: 2.2kΩ carbon-film resistors.
These resistors limit the base current for transistors Q1
to Q2. The base current is the collector current divided by
hFE, but as the transistors are operated in the saturation
region, hFE will drop considerably. Choose the resistors
so that sufficient base current flows.
S VR1 and VR2: 5kΩ to 100kΩ potentiometers for sen-
sitivity and L/R balance adjustment (refer to item 2 of
Circuit operation).
S LED1 to LED12: SLB-26
S C3 and C4: 22µF electrolytic capacitors.
S R1 and R2: 47kΩ carbon-film resistors.
These resistors set the attack and release times (refer
to item 6 of the Circuit operation).
S R8 to R13: 330Ω carbon-film resistors. These resistors
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.
S C5: 0.01µF mylar capacitor.
VCC*VLED*Vsat (Q1*Q4) *VDL
R3: 39kΩ carbon-film resistor.
R8X13 =
ILED
This resistor sets the oscillator frequency (refer to the
Operation notes).
VDL = Display switch output “L” voltage.
S C6: 100µF electrolytic capacitor. This capacitor is
used as a ripple filter. The positive lead should be con-
nected close to VCC (pin 22), and the negative lead
close to the junction of pins 10 and 11.
FCircuit operation
(1) Function
The attack and release times for the display can be set
using external components.
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).
(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.
Independent AC (two channels) and DC (one channel)
inputs are provided, and a control input pin is used to
switch between them.
Pins 1 and 3 have low input impedance, so we recom-
mend that you connect potentiometers (VR1 and VR2:
5kΩ to 100kΩ) in series with the inputs to adjust the bal-
ance between ch1 and ch2 and set the levels.
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.
667
ROHM [ ROHM ]
