Pocket Transistor Amplifier
Intro: 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
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
-wire
-SPST switch
-10k potentiometer
Tools:
-pliers
-metal cutters
-drill
-soldering iron
-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
-wire
-SPST switch
-10k potentiometer
Tools:
-pliers
-metal cutters
-drill
-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!
76 Comments
avishkag30 5 years ago
systemus 9 years ago
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.
kartikkman 7 years ago
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
ItalianJack 7 years ago
NW66 8 years ago
rah187 7 years ago
rah187 7 years ago
Is the sound quality any good? Also, what is the turns ratio on the transformer?
Mrinal 1 7 years ago
will this work for a 55 plasma speaker
mufaddalquaid.ghadiyali 9 years ago
ThomasT7 9 years ago
This should work.
RahulM7 9 years ago
ThomasT7 9 years ago
Both parts of the diagram which say 1.5v+ go to the positive battery terminal, and both grounds go to the negative side. The 1.5v+ are at the top of the drawing attached to the potentiometer and transformer, and the grounds are the triangular patterns of lines at the bottom, descending from the transistor collector and the bottom half of the audio jack.
RahulM7 9 years ago
krstecd12 9 years ago
can you give me a circuit for amplifiler with 2-3 NPN transistors, and circuit for fm audio transmitter without trimmer capacitor. Thanks
GabrielP 9 years ago
Connecting the + and ground with a 100 uf capacitor greatly improves the sound quality and volume.
AbdulM2 9 years ago
hey dear i cant understand the circuit please make it clear that what it ground and where i have to put the batteries ? and can you tell me is it works with an other kind of transformer use to transform current ? like those in mobile charger !! please help
Higgs Boson 9 years ago
The emitter of the transistor, one end of the pot, and the ground pin on the audio jack are connected to ground. Put the battery such that positive is V+ and negative is ground. Power transformers like those in phone chargers will probably not work. Your best bet is to buy a small audio transformer from radioshack, digikey, mouser, etc. The exact ratings aren't critical.
AbdulM2 9 years ago
hey dear i cant understand the circuit please make it clear that what it ground and where i have to put the batteries ? and can you tell me is it works with an other kind of transformer use to transform current ? like those in mobile charger !! please help
AbdulM2 9 years ago
hey dear i cant understand the circuit please make it clear that what it ground and where i have to put the batteries ? and can you tell me is it works with an other kind of transformer use to transform current ? like those in mobile charger !! please help
AbdulM2 9 years ago
hey dear i cant understand the circuit please make it clear that what it ground and where i have to put the batteries ? and can you tell me is it works with an other kind of transformer use to transform current ? like those in mobile charger !! please help