GUITAR MINI-PRACTICE AMP/ HEADPHONE AMP/ PRE-AMP

If you play guitar as badly as I, plugging into a large amplifier can be annoying for the rest of your family. (Or neighbours) Or maybe you don’t want to cough up the big bucks for an amplifier. This little amp solves all those problems. Plug a small speaker into the output and it is loud enough for you to hear but not loud enough to disturb anyone else. Plug a headphone into the output only you can hear it. Plug a patch cord into the output and it acts as a pre- amplifier so you can plug it into your stereo, sound bar or other device for really big sound.

Materials:

LM386 Amplifier kit ( Available from Amazon or other suppliers online. About $10 CDN) Alternatively, there are many Instructables on building a similar amp. This one, however comes with all components and circuit board so it was very convenient.

1/4” audio socket

1/8” audio socket

9V battery clip

9V battery

SPST switch

Hook up wire

Small speaker

solder

Hot glue gun

Duct tape

Small plastic box

Tools:

Fine tip soldering iron

cutting pliers

step drill bit and drill

The kit comes with no schematic but the circuit board is printed with the component locations so it is a simple matter of placing them in their proper orientations, soldering them in place and clipping the excess wire. Note: I eliminated the socket for the battery and soldered directly to the + and - locations. Also I eliminated the audio input socket and soldered the leads from the 1/4” socket directly to the 2 contact points. There are 3 resistors. 2 are the same. Just look at the codes (stripes) to identify the one that is different and place them in the proper marked locations. The speaker output is well marked so just solder the 2 leads directly to the board. Cut the + battery lead (red) and solder the SPST switch in line. I decided to leave the speaker as an external plug- in device and soldered the 1/8" audio socket to the board instead. Once finished, test to see if it works. If not, check all your solder joints.

An easier build than it looks. Just be patient as the parts are extremely tiny.

The plastic is easy to drill and it is just big enough for the components and is small enough to fit in a guitar case. It also has a positive snap lock.

Locate all components where they won’t interfere with each other and mark their locations with a pencil. Use the step drill to make appropriate size holes for attachment. Attach the components with their corresponding nuts (circuit board, input jack, switch. I hot glued the 1/8” phone jack to the box bottom letting it extend through a hole in the side. I used a piece of rolled duct tape where the battery is located as it will keep it from moving around and it allows the battery to be easily replaced.

Do a check with the lid on. The LED should be visible through the translucent lid to remind you the power is on. You may want to add some labels with stick on letters or marker. Make sure all wires are inside the case.

Plug in your guitar and headphones and switch on. Power should come on, indicated by the LED and you should hear whatever you play. You can control the volume with the included control although I like to leave it on high and use the guitar volume control.. Replace the phones with a patch cord and plug into your stereo or sound bar. Make certain to switch your unit to AUX. Now you should hear a really big sound. This unit will also power a small external speaker if you desire a quieter sound.