This document provides instructions for building a simple audio amplifier circuit using only a few basic components. The circuit uses two LM386 integrated circuits to provide amplification with a gain of 200. It can be built and tested on a breadboard before permanently assembling the circuit on a small printed circuit board. The assembled amplifier requires only a 9V battery, audio input, and speaker to operate and provides excellent sound quality with a minimal component design.

1. Simple Amp
A powerfully simple audio amplifier
Gunther Cox 2014, http://salviusrobot.blogspot.com, Creative Commons Attribution 3.0

2. Introduction
This amplifier circuit provides excellent signal
amplification and sound quality. In addition, this
circuit has an extremely minimalistic design and
only uses a few parts.

3. Parts
x2 10uf capacitor *
x2 LM386N-1 *
x1 9V battery clip
x1 9 Volt Battery Clip
x1 9 Volt battery
x1 8 to 16 Ohm speaker
x1 3.5mm audio socket
x1 4-pin connector & corresponding plug
x1 8 pin IC socket
x1 Speaker
* Non-optional items

4. Tools
Solderless breadboard
Thin jumper wire
3.5 mm audio cable
Soldering iron & solder
Miter saw
Pliers / Wire cutters

5. About the LM386N-1
How Integrated Circuit Pins are numbered:
http://salviusrobot.blogspot.com/2012/06/ics-integrated-circuits.html
ICs will almost always have an indicator in the form of a small tab shape, circle or both on one side of the body to indicate the left
side of the chip. With the pins facing down (live bug) and the indicator mark to the left you can count the pins. The pins start at 1
on the bottom left and count up as you go the the right. Then the top row starts counting on the right and goes to the left.
To build this amplifier we are using the LM386N-1 Audio Amplifier IC. This is a pretty usefull chip because it has low voltage
requirements and an excellent amount of amplification. A good way to learn about this chip is to check out the data sheet which is
available if you just do a search for "LM386N-1 datasheet" and you should find that there is plenty available from different
manufacturers.
I'm using the Texas Instruments version of this sheet and they provide some useful hints down near the bottom of the sheet. They
say:
If a capacitor is put from pin 1 to 8, bypassing the 1.35 kΩ resistor, the gain will go up to 200 (46 dB).
So this is pretty useful because this tells us how we can increase the gain for this amplifier. The gain is just the amount that our
amplifier increases the sound signal. By default LM386 chip has a gain of 20 but were going to increase that because we want to
get as much out of this chip as we can.

6. Building the Breadboard Circuit
Building the amplifier on a
breadboard before soldering it
together makes it easier to test
for problems if it turns out that
we made a mistake while
building it.

7. Breadboard setup
Begin by inserting the
two ICs into the
breadboard. The ICs in
the photos have been
labeled to make
referencing them
easier.

8. Connect pins 2 and 4 on IC A to the ground line. Connect pins 3 and 4 on IC B
to the ground line.

9. Connect pin 3 on IC A to pin 2 on IC B. Connect pin 6 on IC A to pin 6 on IC B.

10. Attach the 10 uf capacitors between pin 1 and 8 on each IC. Be sure to connect
the negative side of the capacitor (stripe side) to pin 8.

11. Audio signal tester
This is a tool you can make
to test the breadboard. Use
a cable from a pair of
headphones and connect
both pairs of ground and
signal wires together as
shown. Usually you can find
a friend who has a broken
pair to donate.

12. Connect the ground wire of the audio cable to the ground of your circuit.
Attach the signal wire to pin 2 of IC B.

13. Connect the negative battery wire to ground and the positive wire to the pin 6
jumper. Connect the wire for the speaker between pin number 5 from both ICs.

14. Testing the breadboard circuit
Connect the battery and plug in a radio or mp3 play to test your breadboard circuit. You should hear it working, if not go
back and check to make sure that everything is connected correctly. If you have double checked your work and it is still
not working it is possible that one of the ICs is not working. If that is the case, try switching it out with a new one.

15. Assembling the Amp
The next thing we are going to do is solder the
parts onto a circuit board to make it permanent.
For this step I am going to also use a IC socket
so that I can easily replace the ICs if I ever
need to.

16. Separate the PCB pieces
This PCB board comes with a perforated line down the center where you could
probably snap the two pieces apart. A miter saw can be used to sever the
thatching between the halves resulting in a cleaner edge. Use a block of wood to
elevate the PCB board while you cut it.

17. Place the pins of the IC sockets through the center holes of the PCB board. Flip the
board over and apply solder to the base of each pin to hold the socket in place.

18. 2
1
3
4
5
Solder in the five jumpers as shown. Refer back to the breadboard circuit for
reference.

19. Solder the 9 volt battery clip to the board as shown.

20. Attach the 3.5 mm audio jack to the board as shown.

21. Solder a jumper wire across the two signal leeds of the audio jack. Make sure that this jumper is also
soldered to the jumper between IC A pin 3 and IC B pin 2. The points you must solder have been
indicated in the photo.

22. Use a pair of pliers to bend the bottom right connector pin at a 90 degree angle.
Insert the connector into the PCB board so that the left pin can be soldered to pin 5 of IC A.

23. Solder a jumper from pin 5 of IC B to the bent pin of the connector.

24. Solder the two 10 uF capacitors between pins 1 and 8 on each IC. Be sure to
position the negative polarity indicator on the capacitor on pin 8.

25. Test
Trim off any excess wire and
then insert the ICs into the
sockets. You must insert
them with the polarity
indicator facing the right way
as shown. Plug in an mp3
player or a laptop through
the audio jack and test it out.
Plug your speaker into the
four pin socket.