18 Simple Audio Amplifier using 317IC

Another simple audio amplifier circuit, but this time it uses LM317 regulator IC. The amp can deliver 1W power max and needs only few parts.  This circuit is originally from  vegmatic1966 youtube channel.

schematic diagram of LM317 audio amp

Part List:
C1, C3 - 10uF electrolytic capacitor rated 16V
C2 - 470uF electrolytic capacitor rated 16V
R1 - 470 ohms 1/2W
R2 - 10 ohms 2W
POT1 - 5 kilo-ohms potentiometer
SPK - 8 ohms rated 1W speaker
LM317 - 317 or any similar regulator IC

What to do:
After you assembled the circuit above, adjust potentiometer POT1 until the voltage across R2 is half the supply voltage (around 4.5V). Don't forget adding heatsink in your LM317. Check the polarities and pins of the parts before testing.

Part pinouts:

LM317 pinout

0 Simple Microphone Pre-amplifier Circuit

A cheap pre-amp for microphones using transistors. The input audio signal is amplified around 120 times.

Pre-amp schematic

Part List:

R1, R2, R5 - 120 kilo ohms 1/4W

R3, R6 - 12 kilo ohms 1/4W

R4 - 100 ohms 1/4W

C1, C2, C4 - 100nF capacitor

C3 - 10uF electrolytic capacitor rated 16V

Q1 - 9013, 2N2222 or similar NPN transistor

Q2 - 2N3906 or similar PNP transistor

INPUT - use condenser microphone (electret will not work)

3 Simple Audio Booster Circuit

What this circuit does is boost the audio signal from microphone, guitar or any sound generator. It amplifies signal from millivolts to few volts but it increases also its impedance thus connecting the 8 ohms speaker directly to the output will not work. You can series this circuit to a buffer circuit to convert this high impedance to low impedance.

audio booster schematic

2N222 pinouts

Part List:
R1 - 390 kilo ohms 1/4W
R2 - 47 kilo ohms 1/4W
R3 - 10 kilo ohms 1/4W
R4 - 560 ohms 1/4W
Pot1 - 100 kilo ohms potentiometer
C1 - 330uF electrolytic capacitor rated 10V (min)
C2, C3 - 2.2uF electrolytic capacitor rated 10V (min)
Q1 - 2N2222 or similar NPN transistor

1 9V Amplifier Circuit

Another simple amplifier circuit powered by 9V battery. You can use this for your mp3 players, phone and other audio devices. The circuit can be assemble in a very small size since it has less parts.

amplifier schematic

NA22E, BC369 pinout

2N2222, NA21E, BC368 pinout

Part List:
R1 - 100 kilo ohms 1/4W
R2 - 1 kilo ohms 1/4W
C1 - 33uF electrolytic capacitor rated 10V
C2 - 220uF electrolytic capacitor rated 10V
D1, D2 - 1N914 or similar diode
Q1 - 2N2222 NPN transistor
Q2 - NA22E, BC369 or similar PNP transistor
Q3 - NA21E, BC368 or similar NPN transistor
Spk - 4 ohms to 8 ohms speaker (2W)

Other useful amplifiers:
Simple Hearing Aid - small amp powered by 1.5V
USB amplifier - usefull for computer or laptop speakers

2 USB audio amplifier

Simple amplifier circuit suitable for speakers that can be directly connected to your laptop or computer. The power source is a 5V coming from USB port. The amplifier IC used is TDA2822M of ST Microelectronics.

Part List:
R1, R2 - 10 kilo ohms 1/4W
R3, R4 - 4.7 ohms 1/4W
C1, C2 - 100uF electrolytic capacitor
C3, C4 - 470uF electrolytic capacitor
C5, C6 - 0.1uF electrolytic capacitor
C7 - 10uF electrolytic capacitor
SR, SL - 8 ohms speaker
IC - TDA2822M dual low voltage audio amplifier

0 Simple Hearing Aid

Hearing aid circuit powered by 1.5V battery. The circuit is a simple audio amplifier that pick up sounds then amplifies it to the headphone (Spk).

Part List :
R1 - 3.3 kilo ohms 1/4W
R2 - 120 kilo ohms 1/4W
R3 - 180 kilo ohms 1/4W
R4 - 10 kilo ohms 1/4W
R5 - 4.7 ohms 1/4W
Q1, Q2 - 2N2222 or similar NPN transistor
Q3 - 2N3906 or similar PNP transistor
C1 - 2.2uF electrolytic capacitor
C2 - 4.7uF electrolytic capacitor
Mic - electret microphone
Spk - headphone 8ohms up to 32 ohms
Bat - 1.5V battery

2N3906 pins

2N2222 pins

0 Simple Bass-Boost Circuit using transistor

What this circuit do is allow only low frequency (bass) signal and filter the high frequency out. After the filtering, the signal is amplified. The circuit acts more like a low pass filter. Click diagram to enlarge.

amplifier schematic

Part List:
R1 - 500 kilo ohms 1/4W
R2 - 4.7 kilo ohms 1/4W
R3 - 56 kilo ohms 1/4W
R4 - 56 ohms 1/4W
POT1 - 50 kilo ohms potentiometer
POT2 - 50 kilo ohms potentiometer
C1 - 220uF electrolytic capacitor rated 16V
C2, C5 - 4.7uF electrolytic capacitor rated 16V
C3, C4 - 100nF
Q - 2N2222 or similar NPN transistor
Audio jack - for "signal in" and "signal out"
9V battery

2N2222 pinout

1 Simple Audio amplifier

This circuit uses LM386 ic , a low voltage audio amplifier. This circuit is good in amplifying sound signals as low as 30mV and has a gain around 200 times. You can use this amplifier in intercom projects, guitar amps,and others. Use 8 ohms / 2W speaker.

amplifier schematic

LM386 pins