Pocket Transistor Amplifier





Introduction: Pocket Transistor Amplifier

In this instructable I will show you how to make a simple amplifier that can be used for a variety of different things. Because the 8ohm speakers are very quiet, it wasn't worth connecting a 1/4 in. jack to it for my cello pickup or my dads guitar, so I decided to make ipod speakers with it. When I tried directly connecting the ipod to the speakers the signal was very weak, so I decided to connect it to a very simple transistor amplifier. 

Step 1: Materials

-altoids tin
-small audio transformer (too big makes it sound fuzzy)
-0.1µf ceramic disk capacitor (104)
-2n3904 NPN transistor
-two 8ohm speakers
-battery case for one AAA batttery
-3.5 mm male audio jack
-SPST switch
-10k potentiometer 

-metal cutters
-soldering iron

Step 2: Cut Holes

First you need to cut holes in the altoids tin (or other enclosure you are going to use) for the speakers, the jack, switch, and potentiometer.

Step 3: Make the Circuit

Build the circuit according to the schematic. Connect the capacitor to the base of the transistor. connect the wiper pin of the pot to the base of the transistor, and connect one of the outside pins on the pot to the power supply and the other outside pin to ground. connect the emitter to ground, and the collector to one of the outside wires on the side of the transformer that has three wires coming out. connect the other outside wire on the three wire side to  the the power supply. connect both wires of the speaker to the both of the wires on the side of the transformer that has two wires sticking out of it. don't worry about the audio input just yet. (if you are going to use two speakers connect them in parallel.)

Step 4: Connecting the Jack

When I stripped the wire from the airline head phones, i found one black, one red, and one yellow wires. connect the yellow and red wires. You are going to connect the black wire to ground, and the yellow and red wires to audio in on the circuit from the previous step. Once this is done the circuit is complete.

Step 5: Put Everything in the Tin.

Cover the bottom of the altoids tin where the electronics are going to sit with electrical tape to prevent short circuits. glue your speakers in their holes, and put the pot in a hole drilled between the speakers (only put the knob through the hole.

Step 6: Listening to It

plug your ipod on, put your battery in the speakers, and play some music. you can adjust the volume with either the potentiometer or the ipod's volume control. If you turn the volume on the ipod up too much the sound will get fuzzy, so keep the volume on the ipod up about three quarters of the way, and adjust the volume with the pot. If you have any problems or questions feel free to leave a comment and I will try to help you out. Have fun!



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    People have asked if some different part can replace the transformer. A 2N3906 or 2N2907 PNP transistor (silicon) could replace the transformer. Such a circuit would require at least a three-volt power supply. Nine volts would be even better. You would also need to provide bias for two transistors instead of one. If anyone is interested, I can go into more detail.

    I am interested in making it without the transformer , i want to make it with the help of transistors only . So i just wanted to ask whether the speaker output depend on current or voltage , I mean for connecting two transistor should i use configuration like darlington or cascade connection

    That would be great if you could. I kind of would like to not have to buy materials, and I have 2 each npn and pnp transistors.


    could you post a schematic of that design?

    Well, I made it... It sort of works, but I'm thinking I may have screwed up the audio connection and connected the tip to ground and the sleeve to the input instead of the other way around. This may explian the poor sound quality, and I am not hooking my ipod up to this thing again untill I fix it out of fear that my ipod won't like my reversed audio connection.

    Is the sound quality any good? Also, what is the turns ratio on the transformer?

    will this work for a 55 plasma speaker

    This should work.


    Can you give a circuit diagram also with battery to understand the circuit properly