Mini amps are useful for practicing on the road. If you're home is too small for a small-sized guitar amplifier, using a mini amp is an ideal way to practice without annoying the neighbours. Although convenient and inexpensive, mini amps rarely have incredible tone. This is due to the lack of signal processing and the affordability of the parts. Making your own mini amp is a good way of getting a cheap, portable amp that meets your own spec and personal taste.
- Skill level:
Things you need
- LM 158 operational amplifier (op-amp) circuit
- Wire cutters
- Soldering iron
- 9-volt battery
- 9-volt battery connection
- Mini speaker
- 1/4-inch input jack
- Amplifier housing
Acquire your parts. The options for your amplifier housing are potentially limitless. Smokey Amps make units out of recycled cigarette packets that sound great. You can get your op-amp from the National Semiconductor online store (see "Resources"). You can also salvage a small speaker from an old radio or MP3 player docking station.
Set up a work space. You'll need enough room to lay out your circuit and wires as well as sufficient power supplies to work your soldering iron.
Inspect your parts before assembly. Although this is a rudimentary electronics project, it's important to make sure the parts are in good condition. Carefully examine the op-amp circuit and look out for cracks to the circuit board and loose fitting components.
Connect the input jacks to the op-amp. Strip the insulation on the wires to expose the metal. Then twist the bare ends and solder them in place. One wire connects the input to the 10-ohm resistor on the op-amp circuit, the other wire connects the input jack to the output terminal on the op-amp circuit.
Load the half completed circuit into the housing. Naturally, the speaker must be exposed at the front, and it's smart to locate the jacks on the back. But the configuration and layout of the mini amp are up to you. If you are using a wooden enclosure, measure out the holes need for the speak and the jacks and cut them before loading the circuit. You can strip out all but the speaker from an old stereo and load your new circuit in that. As long as the components are fixed in place and the speaker is exposed at the front, it really doesn't matter.
Connect the op-amp circuit to the speaker. Solder one end of a wire to the output terminal on the op-amp circuit and then connect that to the terminal on the speaker. Ensure that you don't drip any solder on to the board itself, as this can cause solder-bridges that divert the audio signal away from its intended destination. If you do, let it dry, melt it away with the soldering iron and then brush away the residue with an old tooth brush. Connect the 9-volt battery connection to the op-amp circuit and connect a battery. Then enclose the amp housing.
Tips and warnings
- Cut the wire as short as possible to save space.
- Although the amp housing as a matter of preference, it's essential it is water tight and rigid enough to protect the components.
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