What you are building
The LM386 is a low-voltage audio power amplifier. Its input transistor stage biases a tiny AC waveform, its voltage gain stage enlarges it, and its output stage supplies current to a speaker. The output is AC-coupled so the speaker does not receive the chip's DC bias.
There is no “stereo LM386” in this build: stereo means two mono amplifiers. The left and right channels have separate inputs, output capacitors, and speakers; they share the 9 V rails.
Clean speech and music at comfortable tabletop volume. This is a learning amplifier, not a hi-fi power stage: keep the source moderate and use 8 Ω speakers rated for at least 0.5 W.
Safety & prerequisites
Before you touch power
- Use only a regulated or fresh 9 V DC source; never connect mains voltage to a breadboard.
- Power off while moving wires. Confirm polarity and continuity with a multimeter first.
- Electrolytic capacitors are polarized: the stripe marks negative. A reversed part can heat, vent, or burst.
- Keep volume low when testing. Do not short the LM386 output or connect headphones directly.
Workbench kit
- Solderless breadboard and insulated jumper wires; wire cutters/strippers.
- Digital multimeter (DC volts and continuity). Soldering iron is optional.
- Phone, laptop, or audio generator with a 3.5 mm cable/splitter.
- Eye protection and a clear, well-lit, static-safe work area.
Know the difference between polarity (+/−), a node (electrically common holes), and a rail (long power bus). Breadboard center channels are not connected across the gap.
Complete parts list
| Component / part number | Qty. | Purpose / role |
|---|---|---|
| LM386N-1 (or LM386-compatible, DIP-8) | 2 | One low-voltage power amplifier IC for left and right. |
| 10 µF electrolytic, 16 V or higher | 2 | Input coupling; blocks source DC (CIN-L / CIN-R). |
| 220 µF electrolytic, 16 V or higher | 2 | Output coupling; blocks IC output DC (COUT-L / COUT-R). |
| 100 nF ceramic + 220 µF electrolytic | 1 each | Supply bypass: fast noise shunt plus bulk smoothing. |
| 10 kΩ audio/log potentiometer, dual-gang | 1 | One shaft controls left and right volume. Two single 10 kΩ pots also work. |
| 8 Ω, ≥0.5 W speaker | 2 | Left/right loads; observe the output capacitor connection. |
| 9 V battery + snap, or regulated 9 V DC supply | 1 | Single-ended power. Battery is safest for first test. |
| Full-size solderless breadboard + jumper wire kit | 1 + 1 | Interconnects the circuit and keeps both channels serviceable. |
| 3.5 mm stereo plug/breakout (or two RCA inputs) | 1 | Provides L, R, and common signal ground. |
Circuit diagrams
Pin map & assembly
1 = Gain · 2 = IN− · 3 = IN+ · 4 = GND
5 = OUT · 6 = VS · 7 = bypass · 8 = Gain
Outer lug 1 → source ground; outer lug 3 → source L/R; center wiper → 10 µF input capacitor → pin 3. Reverse outer lugs if clockwise rotation feels backward.
Place both ICs
With each DIP notch or dot facing the same direction, straddle the breadboard center gap. Leave a few columns between U1 and U2. Do not trust the diagram's scale; count the DIP pins from the notch.
Create rails and ground
Connect the battery red lead to the red rail and black lead to the blue/black rail. Link split rail sections with jumpers if your breadboard breaks them in the middle. Connect pin 4 of both ICs to ground and pin 6 of both to +9 V.
Bypass the supply
Put the 100 nF ceramic directly between +9 V and ground near the ICs. Add the 220 µF bulk capacitor across the same rails: positive to +9 V, stripe/negative to ground. Keep these wires short.
Wire volume and inputs
Connect the stereo jack sleeve to ground. Feed its L and R tips to the two matching potentiometer outer lugs. Ground the other outer lug of each section. Route each wiper through its own 10 µF capacitor to that channel's pin 3; capacitor positive toward pin 3. Tie each pin 2 to ground. Leave pins 1 and 8 open for default gain 20.
Add the output stage
For each channel, connect pin 5 to the positive side of a 220 µF capacitor. Connect its negative side to the speaker positive terminal. Connect speaker negative to the ground rail. Never omit the output capacitor on this single-supply circuit.
Final inspection
Trace every wire against the pin map, check for adjacent-rail jumpers, and make sure no bare speaker wires touch. Set volume fully down, plug in the source, then connect the 9 V battery last.
Testing & troubleshooting
Safe first power-up
- With battery disconnected, use continuity mode to confirm ground is common and +9 V is not shorted to ground.
- With no audio connected, power up and measure pin 6 to ground: expect about 9 V. Measure pin 5: it may sit near mid-supply; this is normal.
- Measure after each output capacitor: DC should be close to 0 V. If not, disconnect power and recheck polarity/pin numbering.
- Connect speakers and source, start at minimum volume, and increase slowly.
Symptom → likely fix
- No sound: verify IC orientation, pin 3 signal, pin 4 ground, pin 6 supply, and that the source sleeve is grounded.
- One channel only: swap inputs/speakers to isolate the fault; inspect the corresponding pot wiper and output capacitor.
- Hum: shorten ground/power wires, use the battery, and keep input wires away from output wires.
- Whine or squeal: output is feeding input; separate wires, use the 100 nF bypass, and avoid speaker-to-pot wiring loops.
- Hot IC or bulging capacitor: power off immediately; suspect reversed electrolytic, shorted output, wrong rail, or a miscounted pin.
- Distortion: lower source/volume, confirm 8 Ω load, and remember a 9 V LM386 is a small speaker amp.
U1: 2→GND 3←CIN-L←L wiper 4→GND 5→(+ COUT-L −)→SPK-L+ 6→+9V U2: 2→GND 3←CIN-R←R wiper 4→GND 5→(+ COUT-R −)→SPK-R+ 6→+9V Both: pin 1/8 open · speaker negatives, jack sleeve, and supply − → common GND