This project is a 20W Audio amplifier based on LM1875.
This project is designed to operate with minimum of
external components. This amplifier offers high
quality and high performance audio at very low
distortion. Project is based on nationals
LM1875 IC. The IC is thermal and short
The LM1875 is a monolithic power amplifier offering
very low distortion and high quality performance for
consumer audio applications, the project work on
single supply. Device overload protection consists
of both internal current limit and thermal shutdown.
The LM1875 design takes advantage of advanced
circuit techniques and processing to achieve
extremely low distortion levels even at high output
power levels. Other outstanding features include
high gain, fast slew rate and a wide power
bandwidth, large output voltage swing, high current
capability, and a very wide supply range. The
amplifier is internally compensated and stable for
gains of 10 or greater.
Supply 16-48V DC @ 2 Amp
Output 20W into 4Ohm
Thermal Protection with parole circuit
Low distortion: 0.015%, 1 kHz, 20 W
audio signal Input
The preceding suggestions regarding circuit board
grounding techniques will also help to prevent
excessive distortion levels in audio applications.
For low THD, it is also necessary to keep the power
supply traces and wires separated from the traces
and wires connected to the inputs of the LM1875.
This prevents the power supply currents, which are
large and nonlinear, from inductively coupling to
the LM1875 inputs.
Power supply wires should be twisted together and
separated from the circuit board. Where these wires
are soldered to the board, they should be
perpendicular to the plane of the board at least to
a distance of a couple of inches. With a proper
physical layout, THD levels at 20 kHz with 10W
output to an 8Ωload should be less than 0.05%, and
less than 0.02% at 1 kHz
PCB bottom layer