Instructables

Miniature Guitar/Audio Amplifier

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I wanted a small yet robust amp for practicing while I travel. I wanted something that would fit in my pocket yet still be loud enough to hear.

Presented here is a amplifier based upon the LM386 Audio Amplifier.

There is a standard circuit in the data sheet that is an excellent place to start.

Materials needed (digikey part numbers):
 1 - HM359 project box
1 -  668-1237 speaker
1 - LM386N-4 amplifier
1 - BS6I battery conn
1 - CP1-3515 stereo jack
1 - SC1316 stereo jack
2 - 450-1742 knob
1 - 679-1856 switch
1- 3mm LED
1 - 10 ohm 1/4W resistor
1 - 10uF ceramic cap
1 - .05 uF ceramic cap
1 - 420 uF electrolytic cap
1 - 8 ohm resistor
2 - 51AADB24 10K pot
1 - HM1252 circuit board

wire and solder
lm386.pdf303 KB
 
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Step 1: Prep the enclosure

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Careful planning is required the first time you free build a circuit. The circuit board has solder pads but not traces. You will have to use thin wire to make the connections for the circuit to work.

Begin by laying out the components on the circuit board that will need to pass through the enclosure. This enclosure has a removable top panel which will be used for the volume, gain and 1/4 inch stereo jack.

Space is limited to check for fit before drilling.

All drilling of the plastic should be done with a step drill bit. This will make the cleanest holes without breaking the plastic.

Lay out the pots a few spaces back but still in line with the desired position. mark the center of each pot shaft then drill with a step drill tot he tightest fitting hole size. Make a center mark between the pot holes then drill for the stereo jack

On the inside of the top cover position and mark where the speaker will go.

Make a template on grid paper the same size as the speaker.

Tape the template to the inside of the cover as shown then use a step bit to drill holes on the center of every square in the grid. This will form the speaker grille. clean up the holes.



accampoy1 month ago

could you complete the schematic diagram. i really want to build this!

Acdccruz7 months ago
Could you tell me how many decibels it reaches at maximum volume
Random_Canadian (author)  Acdccruz6 months ago
Not sure, I'd have to check the datasheet for the amplifier and speaker.
Very professional looking end product, and well written ible. Great technique using the graph paper as a ready made template for locating equally spaced grill holes.
veeguy1 year ago
I built a guitar amp using roughly the same circuit as yours. I am very happy with it. What I wanted to add here is that I used an old walkie-talkie for the case and housing. It already had a speaker and speaker grill, a battery compartment and two pots I reused (volume/on/off and squelch) and I used the antenna hole for my 1/4" input jack. I did replace the cheapo speaker with a better unit, but it really cut down on the parts I needed to buy. It ended up looking very "factory made" and it even has a belt clip!
Have you considered adding a preamp stage using an LM741 in inverting mode? It would be just a few extra parts, but would probably improve the audio quality.
Random_Canadian (author)  RetroTechno1 year ago
I actually tried a variation of this circuit using a SSM2019 audio pre-amp and another using an ICL7662 to provide negative voltage. The circuits worked with no discernible improvement the one presented here.

This circuit is remarkably crisp and clean sounding until you start clipping the audio with too much gain.
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