Saturday, October 10, 2020

HI-FI 30W Audio Power Amplifier using LM1875 IC + PCB

Figure 1 - PCB Hi-Fi 30W Power Amplifier LM1875

The amplifier presented, is a hi-fi amplifier based on the Integrated Circuit LM1875, which is a monolithic power amplifier offering very low distortion and high-quality performance for consumer audio applications.

General Description

The LM1875 delivers 20 watts into a 4Ω or 8Ω load on ±25V supplies. Using an 8Ω load and ±30V supplies, over 30 watts of power may be delivered.

The LM1875 is a wide power amplifier with very low distortion and high-quality efficiency for audio applications, the amplifier is designed to operate with a minimum of external components.

Device overload protection consists of both internal current limit and thermal shutdown.

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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 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.


  • Up to 30 Watts Output Power
  • AVO Typically 90 dB
  • Low Distortion: 0.015%, 1 kHz, 20 W
  • Wide Power Bandwidth: 70 kHz
  • Protection for AC and DC Short Circuits to Ground
  • Thermal Protection with Parole Circuit
  • High Current Capability: 4A
  • Wide Supply Range 16V-60V
  • Internal Output Protection Diodes
  • 94 dB Ripple Rejection
  • Plastic Power Package TO-220


  • High-Performance Audio Systems
  • Bridge Amplifiers
  •  Stereo Phonographs
  • Servo Amplifiers
  • Instrument Systems

The connection diagram or if you prefer, the pinout of the LM1875 is shown in Figure 2 below.

Figure 2 - Pinout LM1875 Audio Amplifier
The circuit diagram is in Figure 3 below, as we can see, there are few numbers of external components, making the assembly of this amplifier very easy.
Figure 3 - Schematic Audio Power Amplifier IC LM1875

Power Dissipation and Heat Sink

The LM1875 must always be operated with a heat sink, even when it is not required to drive a load. Assumes the use of a heat sink having a thermal resistance of 1°C/W and no insulator with an ambient temperature of 25°C. 

Because the output limiting circuitry has a negative temperature coefficient, the maximum output power delivered to a 4Ω load may be slightly reduced when the tab temperature exceeds 55°C.

Component List

  • U1 ......... LM1875 Integrated Circuit.
  • R1 ......... 1MΩ 1/8w Resistor (brown, black, yellow, gold)
  • R2 ......... 22KΩ 1/8w Resistor (red, red, orange, gold)
  • R3 ......... 1KΩ 1/8w Resistor (brown, black, red, gold)
  • R4 ......... 20KΩ 1/8w Resistor (red, black, orange, gold)
  • R5 ........  1Ω 1/8w Resistor (brown, black,  gold)
  • C1 ......... 2.2µF Polyester capacitor
  • C2 .....… 25V  22µF Electrolytic capacitor
  • C3, C4 ... 0.1uF Ceramic capacitor
  • C5 .......... 0.22uF Ceramic capacitor
  • C6, C7 ... 70V  100µF Electrolytic capacitor
  • P1, P3 .... Screw Terminal Block: 2-Pin, 5 mm
  • P2 .......... Screw Terminal Block: 3-Pin, 5 mm
  • Others .... printed circuit board, heat sink, box, tin, wires, etc.

Printed Circuit Board

The layout of the Printed Circuit Board is shown in Figure 1, and we have all the necessary files for you to be able to print your PCI, with the GERBER files, PDF Layout, JPG. All with a direct link for you to download and assemble yours.

Downloadable files

Files: Gerber, Layout in PDF, PNG, to download. Direct link: Click Here!

If you have any questions, suggestions or corrections, please leave them in the comments and we will answer them soon.

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