Introduction: Building an Audio Amplifier

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A general purpose audio amplifier is very handy in many projects that are related to audio. This project, which can be completed within a few hours, is a more advanced version of the simple LM386 based amplifiers projects normally found as provides a safe connection to external devices (e.g., smartphones, PCs etc.) and provides a x200 gain which allows you to connect weak audio sources (like headset sockets) to speakers.

The circuit is based on the LM386 IC (see specs) and supports a single channel (mono).

Step 1: The Parts

To build this circuit, you'll need the following parts:

  • LM386 IC + 8Pin DIP SIP Round IC Sockets Adaptor - link and link
  • R1 = resistor 1K Ohm
  • R2 = resistor 10 Ohm
  • R3 = POT Trimmer 10K Ohm - link
  • R4 = resistor 10K Ohm
  • C1 = 10 uF electrolytic
  • C2 = 0.1 uF ceramic (104)
  • C3 = 0.1 uF ceramic (104)
  • C4 = 220 uF electrolytic
  • C5 = 0.05 uF (503) - I used 2x 104 capacitors in series as I didn't have a 503.
  • T = Audio Output Transformer 1K:8 to 32 ohm - link
  • PCB prototype paper - link
  • SW = SPDT switch - link
  • 3 Pin Plug-in Screw Terminal Block Connector - link
  • Audio female jack 3.5mm - link
  • D = LED

(the attached image shows only some of the parts...)

Step 2: Circuit and Schematics

The design provides 2 options for imputing audio, using the audio jack or the block connector (which are connected in parallel) and the same applies to the output. This flexibility will make it easier to connect the amplifier to different sources.

The input audio is connected to an audio transformer and not directly to the amplifier circuit. This is an important aspect in the design as it completely separates between the source device (e.g., smartphone, PC) voltage and the amplifier circuit (which runs on 9V) and by that protect the source device.

The output may be connected to a speaker, headset or another circuit / project.

The amplifier can be powered by +5 to +9V.

The POWER OUT connector can be used to connect additional circuits (for example, laser modulator) to the same power source while using a common ground.

Step 3: The PCB

The atached PCB layout is suitable for a PCB prototype paper (and not a real PCB). I used a 7x5 cm PCB but you can use any size you like.

Step 4: The Result

Check out the video to see the circuit in action and hear the sound quality.