How to Build Your Own Portable Guitar Amplifier

This electronic circuit will allow you to hear your electric guitar more easily.

Electric guitars are not designed to be played without an amplifier. However, even practice amplifiers can be too expensive for some people to purchase. It is possible to build a homemade amplifier out of a few common electronic components. For this reason, some guitarists choose to build their own practice amplifier.

Things You'll Need

• Wood box with removable panel
• Saw
• 6-inch speaker
• Screwdriver
• Wood screws
• 12-volt, 1-amp DC power adapter with bare wire ends
• Electrical pliers
• Electrical wire
• 1-kiloohm resistor
• 100-kiloohm resistor
• Electronic solder
• Soldering iron
• LM358 operational amplifier integrated circuit (also called an op-amp)
• Audio jack (1/4 inch, flush mount)
• Vinyl electrical tape
• Wood block
• Wood glue

Instructions

1. Remove the panel from the wood box. Cut a hole at the front of the box that is at least six inches in diameter and insert the speaker into the hole.

2. Insert a screw into each of the speaker mounting holes. Attach the speaker to the box.

3. Cut six pieces of wire, with each segment being six inches long. Strip 1/ 2 inch of insulation from the ends of each wire segment.

4. Solder one end of the first wire to one of the speaker's electrical terminals. Solder one end of a second wire to the remaining speaker terminal.

5. Drill a hole in the top of the wood box and insert the audio jack, input side facing out. Drill a hole in the removable panel and route the DC adapter wires through it.

6. Drill eight holes in the wood block to correspond with the eight legs on the op-amp. Place the op-amp label-side up into the wood block so that only the top metal parts of the op-amp legs are exposed.

7. Twist together one end of the first wire with one of the leads from the 100-kiloohm resistor. Solder the twisted wire pair to the output terminal (pin 1) on the op-amp.

8. Twist together the free lead from the 100-kiloohm resistor with one of the leads from the 1-kiloohm resistor. Solder the twisted wire pair to the inverting input terminal (pin 2) on the op-amp.

9. Solder one end of the third wire to the tip terminal on the audio jack. Solder one end of the fourth wire to the sleeve terminal on the audio jack.

10. Solder the loose end of the third wire to the non-inverting input terminal (pin 3) on the op-amp.

11. Solder one end of the fifth wire to the "GND" terminal (pin 4) on the op-amp. Twist together one end of the sixth wire with the free lead from the 1-kiloohm resistor and solder the electrical joint.

12. Solder the positive DC adapter wire to the "V+" terminal (pin 8) on the op-amp.

13. Twist together the loose ends of the second, fourth, fifth, and sixth wires with the negative wire from the DC adapter. Solder this electrical joint, and cover it with electrical tape.

14. Cover the exposed metal parts of the op-amp circuit with a piece of electrical tape. Glue the bottom of the wood block to the inside bottom of the wood box. Allow the glue to dry completely.

15. Reinstall the panel to enclose the amplifier circuit. To use this amplifier, plug the adapter into a wall outlet, and plug the guitar into the audio input jack. Use the guitar's volume control knob to control the amplifier's output volume.

References

• Georgia State University: Op-Amp Varieties
• National Semiconductor: LM158/LM258/LM358/LM2904 Low Power Dual Operational Amplifiers