For guitar players, the urge to practice or jam can strike anytime, anywhere. While full-sized amplifiers deliver powerful sound, their size and need for mains power can be limiting. Enter the Portable Guitar Amp, a compact and battery-powered solution that lets you unleash your riffs on the go. In this guide, we’ll show you how to build your own mini marvel, perfect for practice sessions, travel, or just having fun.
Parts You’ll Need to Build Your Portable Guitar Amp
Creating your own portable guitar amplifier is a rewarding project, and it starts with gathering the right components. Here’s a comprehensive parts list to get you started:
- B1 – 9 Volt Battery & Clip: Provides portable power to your amplifier.
- C1 – 4.7μF 16v Capacitor: Coupling capacitor to block DC voltage.
- C2 – 100μF 16v Capacitor: Power supply filtering capacitor for stable operation.
- C3 – 470μF 16v Capacitor: Output capacitor to block DC voltage from the speaker/headphones.
- C4 – 10μF 16v Capacitor: Gain control capacitor, part of the RC network.
- D1 – Green Diffused LED: Power indicator LED (any color will work).
- J1 – ¼” (6.5mm) Mono Jack: Standard guitar input jack.
- J2 – 1⁄8″ (3.5mm) Stereo Headphone Jack: Headphone output for silent practice.
- R1 – 1kΩ ¼-watt Resistor: Current limiting resistor for the LED.
- R2 – 10kΩ ½ watt Potentiometer: Variable resistor to control the amplifier’s gain/volume.
- SP1 – 8Ω ½ watt Speaker (2¼” diameter): Miniature speaker for audio output. A speaker from an old PC works perfectly.
- SW1 – DPDT “on-off-on” Mini Toggle Switch: Special switch for power and output selection (speaker/headphones).
- U1 – LM386N-1 Low Voltage Audio Power Amplifier IC: The heart of the amplifier circuit.
- Misc.: Breadboard and jumper wires (for prototyping), hookup wire, small perfboard, solder, potentiometer knob.
Finding Your Components: Essential Parts and Where to Source Them
While most components are readily available, the speaker (SP1) and the switch (SW1) have specific requirements for this portable guitar amp project.
Speaker (SP1): You need a small 8Ω speaker, around ½ watt, and crucially, about 2¼” (60mm) in diameter to fit within a compact enclosure. Many older PCs used speakers of this size, making them a great source for repurposing. If you’re buying new, consider these options:
- Jameco #135765
- Jameco #10840
- All Electronics #SK-285](http://www.allelectronics.com/make-a-store/item/SK-285/2-1/4-SPEAKER-8-OHM//1.html)
Switch (SW1): The DPDT “on-off-on” mini toggle switch is essential for selecting between speaker output, headphone output, and turning the amplifier off. Look for a mini or sub-mini size with solder lug terminals for easy wiring. Here are some sources:
- Radio Shack #275-664
- Jameco #21952
- All Electronics #MTS-120PC](http://www.allelectronics.com/make-a-store/item/MTS-120PC/DPDT-ON-OFF-ON-MINI-TOGGLE//1.html)
- Futurlec #DPDT101](http://futurlec.com/Switches/DPDT101pr.shtml)
For the remaining components, consider online electronics retailers like Futurlec for cost-effective options. Buying components in bulk, like capacitor or resistor packs, can be a budget-friendly way to stock up for future projects too.
- Battery Clip: Futurlec #9VBATTCLIP
- Capacitors: Futurlec (Various links provided in original article)
- LED: Futurlec #LED5R
- Jacks: Futurlec (Various links provided in original article)
- Resistors: Futurlec #R001K14W
- Potentiometer: Futurlec #POT10K
- LM386N-1 IC: Futurlec #LM386N-1
Understanding the Circuit Schematic
The core of this portable guitar amplifier is the LM386 audio amplifier IC. This chip is known for its simplicity and efficiency, delivering good sound quality with minimal external components. The LM386N-1 version used here provides around 250-325mW of output power, which is ideal for practice and portable applications. For even more power (700mW to 1W), you could use the LM386N-3 or N-4 versions, but ensure your speaker is appropriately rated and avoid using headphones at high volumes with these higher power chips.
Let’s break down the schematic:
-
Input Stage: The guitar signal enters through the ¼” jack (J1) and passes through the capacitor C1 (4.7μF). This capacitor blocks any DC voltage from the guitar signal, allowing only the AC audio signal to proceed. This AC signal then goes to the non-inverting input (pin 3) of the LM386.
-
Amplification Stage: The LM386 (U1) amplifies the audio signal. The inverting input (pin 2) is connected to ground, along with the chip’s ground pin (pin 4).
-
Output Stage & Switching: The amplified audio output from the LM386 (pin 5) is fed through capacitor C3 (470μF). Similar to C1, C3 blocks DC voltage from reaching the speaker or headphones. This output then connects to the DPDT switch (SW1).
-
Speaker/Headphone Selection: The DPDT switch (SW1) directs the audio signal to either the speaker (SP1) or the headphone jack (J2). In one switch position, the signal goes to the speaker; in the other, it’s routed to the headphones. The center position is ‘off’, disconnecting both outputs.
-
Power Supply & Indication: The other side of the DPDT switch (SW1) acts as the power switch. It connects the 9V battery (B1) to the LM386’s power pin (pin 6). A filtering capacitor C2 (100μF) is placed across the power supply rails to smooth out voltage fluctuations and reduce noise. The LED (D1) and resistor R1 (1kΩ) form a simple power indicator circuit, lighting up when the amplifier is switched on.
-
Gain Control: The series RC circuit consisting of capacitor C4 (10μF) and potentiometer R2 (10kΩ) provides adjustable gain. By varying the potentiometer R2, you change the gain of the amplifier, allowing you to go from a clean tone to a distorted overdrive. Experimenting with the values of C4 and R2 can fine-tune the gain characteristics to suit your guitar and playing style.
By carefully assembling these components according to the schematic, you’ll have a functional portable guitar amp that’s perfect for practicing anywhere. Adjusting the gain potentiometer and your guitar’s volume controls will allow you to achieve a range of tones, from clean sounds for headphone practice to overdriven tones when using the speaker.
