Hello Im semi new to electronics but i've used a transistor before to amplify"" input signals and power leds but for some reason i can not get my circuit to work it acts like the transistor is not there i've tried all kinds of peoples online amp circuits and a/ab/c amps but i can not get it to acknowledge the transistor power will not flow thru it i hook it up fine with just the headphone jack and the mp3 players power it works but as soon as the transistor is hooked up it wont work unless the powers on the same pin i dont have a schematic editor to show u i've hooked up a new jack and new speakers and nothing i tried powering the middle trans pin with the arduino like a switch nothing just like my trans is bad but ive used new ones and then I tried pnps nothing still but it powers it and plays music fine with just the hook ups from my player so it should not be the amount of power right ? thanks for any help sorry for my grammar
oh yea the speaker im using now is a 5 W 8 ohm dont know if that matters since it powers fine but kinda quiet off just the player thanks again for any help
It's really hard to help you without seeing what your really doing if your trying to increase output to speaker.
you really need more then a transistor.
Something like this may give you enough output to your speaker.
Even better would be
http://www.ebay.com/itm/Low-Voltage-Audio-Mono-Amplifier-Module-NJM386D-LM386-/201145413441?hash=item2ed5336f41
ive used caps and resistors but i was trying to make it with out a chip here is one persons circuit ive tried but i failed
thanks for taking time out of your day to help that diagram is just the last one ive tried to get to work
i also tried to calculate the need of the speaker even tho i worked without a amp i used this guys calculations for my speaker i for some reason cant get my transistor to act right heres the link to the calculations >> arduino - How many volts can a 1 Watt 8 ohm speaker take? - Electrical Engineering Stack Exchange
Your keyboard seems to be missing some punctuation, like periods "." and commas ",".
Here are some extra for you to use. Punctuation helps people to make sense of gibberish.
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SB_Technology:
I don't have a schematic editor
A pencil sketch photographed with a phone camera is sufficient. It's actually more useful than showing somebody else's schematic. The exercise in sketching it out often discovers errors in your wiring.
The example shown with a single transistor won't work. You could probably make a squawk sound with that but it's really not going to do anything else.
If you want to keep it simple, then you need to use a pre-made module like the LM368 or maybe this: Dual/Quad Power Amplifier - STA540. Follow the example circuit shown in the datasheet and it should be very simple to use.
jremington:
Your keyboard seems to be missing some punctuation, like periods "." and commas ",".Here are some extra for you to use. Punctuation helps people to make sense of gibberish.
.......................... ,,,,,,,,,,,,,,,,,,,,,,,,,
just the headphone jack and the mp3 players power it works but as soon as the transistor is hooked up it wont work unless the powers on the same pin
What? ? ? ? ?
Are you connecting the Arduino or something else?
The circuit in post #3 will work with PWM, but it's not a linear amplifier and it won't work properly with "normal audio" from an MP3 player, or from your soundcard, etc.
If you don't want to build your own amplifier, "computer speakers" are active/powered (with an amplifier built-in), so a set of computer speakers is the easiest solution. That will work with "clean audio" from an MP3 player or with PWM from the Arduino. (With the Arduino, you should put a capacitor in series to block the DC, but the amplified speaker probably as an internal capacitor already.)
Or, you can buy a [u]little amplifier[/u] (or a big amplifier ).
If you really want to build an amplifier, there are plenty of amplifier chips. Simply follow the suggested schematic on the chip manufacturer's datasheet. ...But, that might be a little too advanced for you right now.
It's possible to build a linear amplifier with discrete transistors, but with the availability of cheap and easy-to-use integrated circuits it's not economical or practical (unless you want 200 Watts or something like that).
DVDdoug:
What? ? ? ? ?Are you connecting the Arduino or something else?
The circuit in post #3 will work with PWM, but it's not a linear amplifier and it won't work properly with "normal audio" from an MP3 player, or from your soundcard, etc.
If you don't want to build your own amplifier, "computer speakers" are active/powered (with an amplifier built-in), so a set of computer speakers is the easiest solution. That will work with "clean audio" from an MP3 player or with PWM from the Arduino. (With the Arduino, you should put a capacitor in series to block the DC, but the amplified speaker probably as an internal capacitor already.)
Or, you can buy a [u]little amplifier[/u] (or a big amplifier
If you really want to build an amplifier, there are plenty of amplifier chips. Simply follow the suggested schematic on the chip manufacturer's datasheet. ...But, that might be a little too advanced for you right now.
It's possible to build a linear amplifier with discrete transistors, but with the availability of cheap and easy-to-use integrated circuits it's not economical or practical (unless you want 200 Watts or something like that).
i was trying not to use the arduino board for this so i could make it cheaper for possible Christmas gifts but i could not get it to work by amplifying the signal alone with the npn and some caps and resistors for some reason i was not able to get the transistor to "turn on" i decided to use the arduino board to power the base as a switch to turn on the transistor still would not work to get sound out im willing to to build a amp circuit if u got one i got some parts just not ICs i know im confusing sorry 
heres one i made its not right but maybe someone can point me in the right direction
well for some reason it wont let me post my picture of the circuit i made yea it wont let me add it tried again sorry
tried again to make a amp but again once the transistor is plugged up or a diode or a resistor it wont work the only way i can get it to work is plugging the mp3 cords directly to the speakers i cant be the only one with a problem like this but cant find anything about it online i mean i have music then plug a transistor up gone no music like its cutting it off ive tried mp3 cord to base to collector to emitter nothing no matter how many times i plug it up it cuts the music off instantly no static no humming nothing my transistor cant be bad ive replaced them over and over
The circuit you showed us will switch on and off with a digital input, but will not work satisfactorily with the analogue output of an mp3 player.
You need to "bias" the transistor into it's linear operating region, by having resistors between the supply and the base, and between the base and ground.
Otherwise the transistor will only conduct when the input voltage is greater than +0.7V.
Are you wanting to use pwm to make sound ?
not sure if that is mp3 player out put since im newish im guessing not i tried using the extra resistors in the one circuit still could not get it to work
So lets see ardunio mp3 player is sending out sound how ?
Or are you trying to make amp for mp3 player.
mp3 player lol 
i was gonna see if i had the parts to make a Christmas gift out of a cheap pair of speakers and i dont have a pot or ic chips thanks for the reply tho and i appreciate any help u can give