DIY Kit 139. Stereo 1W audio amplifier with DC volume control
The TDA7053A is an integrated stereo audio power
amplifier with DC volume control in a 16-pin dual-in-line
plastic package. It is designed for use in TVs and
monitors but is also suitable for battery-operated
equipment.
The circuit used is straight out of the data book. PCB
dimensions are a tiny 43mm x 40mm (1.7” x 1.6”).
TDA7053A SPECIFICATIONS
4.5 - 18V supply voltage range
1.5A max non-repetitive peak output current
1.25A max repetitive peak output current
1.1W output power using 6V supply into 8
load
(THD = 10%)
20k
internal input impedance
210uV noise output voltage
20Hz to 300kHz bandwidth (typical) at –1 dB
The kit is constructed on single-sided printed circuit
board. Protel Autotrax & Schematic were used.
CONSTRUCTION
Start with the two resistors followed by the small
monobloc capacitor. Next comes the IC socket with the
electrolytic and polyester capacitors last. Be careful to get
the electrolytic capacitors in the right way around. The
positive lead is marked on the overlay. The negative lead
is marked on the body of the capacitor.
Solder the power and audio cables (supplied by you)
directly to the pads provided on the PCB.
CIRCUIT DESCRIPTION
All the work is done internally in the IC. The internal
circuit consists of a differential input stage with integrated
DC volume control, two class AB output stages and a
stabiliser circuit.
Resistors R1 and R2 provide a DC input impedance to
ground. The input signal is AC coupled into the amplifier
via capacitors C3 and C4. The output stages are a BTL
(Bridge Tied Load) configuration, resulting in increased
output power at low supply voltages.
The gain of each amplifier channel is controlled by the
DC voltage level on pins 2 and 8. This voltage is derived
from the DC supply using a simple voltage divider
network of resistor R3 and potentiometer VR1. Capacitor
C5 across the potentiometer provides power supply
decoupling of the volume control inputs. If the DC
volume control voltage falls below 0.4V the chip will
switch to mute mode.
The maximum voltage gain of the amplifier is internally
fixed at 40.5dB. The DC volume control has a logarithmic
characteristic. The total gain can be controlled from +40.5
to –33 dB.
Due to the BTL output configuration the outputs are
floating with respect to ground.
Therefore the outputs of
the amplifier should never be connected to ground.
Capacitors C1 and C2 provide power supply decoupling.
IF IT DOES NOT WORK
Poor soldering (“dry joints”) is the most common reason
that the circuit does not work. Check all soldered joints
carefully under a good light. Re-solder any that look
suspicious. Check that all components are in their correct
position on the PCB. Are the electrolytic capacitors the
right way round?
PARTS LIST – K107A
Resistors (0.25W carbon)
4K7 yellow violet red ......... R1,2 .............................. 2
27K red violet orange ......... R3 ................................. 1
Capacitors
100nF monobloc 104 .......... C1 ................................. 1
470nF polyester 474 ........... C3,4 .............................. 2
1uF 16V electrolytic ........... C5 ................................. 1
220uF 25V electrolytic ....... C2 ................................. 1
Semiconductors
TDA7053A ......................... IC1 ................................ 1
Stereo Audio Amplifier IC with DC volume control
Miscellaneous
Potentiometer, 10K............. VR1 .............................. 1
Single gang, PCB mounting
IC socket, 16 pin, for mounting IC1 .......................... 1
PCB, K139................................................................. 1
Web Address & Email
You can email us at
peter@kitsrus.com
if you have
any problems or requests. See our Web page at:
http://kitsrus.com
The Data Sheet for the TDA7053A may be downloaded
from the software download page on our website. Note the
‘A’ suffix is important. The TDA7053 with no suffix is a
different IC and is used in our Kit 107.
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