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Mini amplifier with LM386
Small audio amplifier for phone, MP3 player or microcontroller: the LM386 drives an 8 Ω speaker, a trimmer sets the volume. Runs on 6 to 12 V, gain 20.
- Size
- 66 × 48 mm, 1.6 mm thick
- Material
- Circuit board (FR4)
- Difficulty
- Intermediate
- Milling time
- approx. 20 min
- Bits
- Engraving bit 30°, PCB drill Ø 0.8 mm, PCB drill Ø 1.3 mm, Corn cob router bit Ø 2 mm
- Customise
- Fixed template, freely editable once opened
Free with an account · carve with Chrome or Edge · no installation
Build instructions
Parts
| Qty | Part | Value | In layout |
|---|---|---|---|
| 1 | Resistor 0.25 W | 10 Ω Colour bands: brown, black, black, gold | R1 |
| 1 | Trimmer, vertical | 10 kΩ | P1 |
| 1 | Electrolytic capacitor Polarised: the stripe on the case is minus, the long lead is plus (square pad). | 220 µF / 16 V | C1 |
| 1 | Ceramic capacitor | 47 nF | C2 |
| 1 | Ceramic capacitor | 100 nF | C3 |
| 1 | Electrolytic capacitor Polarised: the stripe on the case is minus, the long lead is plus (square pad). | 100 µF / 16 V | C4 |
| 1 | Audio amplifier IC Notch towards the mark in the layout; solder the socket first and insert the IC last. | LM386 | IC1 |
| 3 | Screw terminal 2-pin, 5.08 mm pitch | X1, X2, X3 | |
| 1 | IC socket DIP-8 | ||
| 1 | Speaker 8 Ω, 0.5 W or more |
You also need: soldering iron (about 30 W, fine tip), 0.5 to 1 mm solder with flux, side cutters and a multimeter.
Assembly
- Mill the board: isolate the copper first, then drill, and finally mill out the holes and the outline. The order is shown in the Milling panel.
- Cut through the holding tabs, deburr the edges and rub the copper bright with a scouring pad. After that, do not touch the copper side with your fingers.
- Use a magnifier and a continuity tester to look for leftover copper between neighbouring traces; cut any bridges with a craft knife.
- Insert the parts from the side without copper and solder them on the copper side. Fit low parts first: resistors and diodes, then sockets and transistors, and finally capacitors, terminals and large parts.
- Before soldering, compare the polarity with the component layout: band of the diodes, flat side of the LEDs, minus stripe of the electrolytic capacitors, notch of the ICs.
- Solder each lead for about two seconds at around 330 °C: tip on pad and lead, feed solder until it flows all round. Then clip the leads just above the joint.
- R1 and C2 form the Zobel network at the output; do not leave them out, otherwise the amplifier may oscillate.
- Fit the large electrolytic capacitor C1 with plus towards the IC (minus towards the speaker), and C4 with plus towards the supply.
- Visual check: no solder bridges, no dull, balled-up joints. Remove flux residue with isopropyl alcohol and an old toothbrush.
Test and power up
- Before switching on for the first time, check with the meter that there is no short between plus and minus of the supply. Power up the first time on a bench supply with current limiting if possible.
- Press the LM386 into the socket with the notch towards the mark.
- Speaker to X3, signal source to X1 (signal to IN, ground to GND), turn P1 down.
- Apply 9 V to X2, feed in music and slowly turn up the volume. If it hums, use a shielded cable to the signal source.
- Finally protect the copper side against oxidation with solder lacquer or plastic spray.
How to carve this template
- OpenOpen the template in the app and adjust size and text if you like.
- CheckLook at it in 3D, check run time and warnings.
- Set upThe carve wizard guides you through material, clamping, bit and zero point.
- CarvePress start; the app drives your Grbl router directly over USB.
