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Friday, January 24, 2020

Building high performance 70 Watt audio power amplifier with mute function


In this post, I will share the details on how to make a high performance 70 Watt 
audio power amplifier with mute function using IC LM3886TF.

Video

You can check the video for assembly of the amplifier & also for the testing of the 
amplifier

Theory

The main component of the amplifier is LM3886TF which is a high-performance
audio power amplifier with mute function. The IC package which I used in my video
is 11 pin T220 plastic package. The IC can deliver 68-watt continuous average 
power to a 4-ohm load & 34-watt average power to an 8-ohm load.
The other main components are the voltage regulators LM317 & LM337. Where 
LM317 provides positive voltage & LM337 provides negative voltage ranging from 
1.2 to 37 & -1.2 & -37 respectively.

Features of the amplifier

  • LM3886TF has a wide input supply range (20v to 94v)
  • The amplifier comes with a Mute Function
  • Signal to Noise ratio greater than 92dB
  • LM3886TF has Output short circuit protection built into it
  • Input supply under-voltage protection
  • The design I shared needs a supply voltage between 20v to 40v input supply for the amplifier to work
  • The amplifiers power circuit is also protected from both input & output short circuit

Things & Components you need

  • 1 * LM3886TF
  • 1 * LM317
  • 1 * LM337
  • 8 * 1N4007
  • 1 * Electrolytic Capacitor 22uF/50v
  • 2 * Electrolytic Capacitor - 1000uF/50v, 10uF/50v
  • 3 * Electrolytic Capacitor - 100uF/50v
  • 1 * Ceramic Capacitor - 0.1uF
  • 2 * Ceramic Capacitor - 0.22uF
  • 2 * 5k Trimmer
  • 1 * 10k Normal Pot or Logarithmic Pot
  • 1 * 22k Ohm
  • 2 * 120 Ohm, 1k Ohm
  • 1 * Slide Switch
  • 1 * 220v to 24-0-24 1 Amp transformer
  • Speakers, Connectors & other switches

Affiliate Links

Banggood
Amazon India
Amazon USA & UK
AliExpress

Making

You can create the circuit on a perf board or order a professional PCB board by 
downloading the Gerber file shared at the bottom of the page. I recommend using 
a professional board so you can avoid unwanted noise in the output. The Gerber 
file shared was created using KiCad software which is one of the recommended 
CAD software by the fabricator that I am using. The fabricator that I am using is 
JLCPCB.con you can check them by Clicking Here, they provide very good quality 
PCB board for a very cheap price. After you receive the board assemble the board 
as shown in the video.

Once the board is assembled connect all the connectors which are necessary like 
RCA Jacks, Slide switch for mute function.

Once all the assembly is done, the first thing you need to adjust is the input
voltage. The input voltage should be above 20v. To adjust the positive voltage
connect two wires to the V+ & Gnd on the board at TP(Test Point) & then connect
the wires to the multimeter & adjust the voltage using the trimmer RV1. Now 
similarly adjust the negative voltage, but this time change the wire of V+ to V- & 
adjust the voltage using the trimmer RV2. This is a one time process.

Things to know about

In the circuit, RV3 is used for controlling the volume. J2 is the Audio input from
your laptop or mobile phone. SW1 is used for mute function. You can also change
the value of capacitor C8 to change how the amplifier sounds. My recommend
value is 22 or 47uF. Also, note LM3886TF has to be attached to a big heat sink
since it heats up when used for a long time. Also, add a small heat sink to the
voltage regulators.

Circuit Diagram





Thank you for reading !!!

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