I started electronics recently and I'm trying to make the most basic mp3 amplifier. I try to amplify the music from my phone to the speaker. My phone already amplifies the sound when I connect it directly to the speaker.

I saw that people mostly use lm386 chips but I don't have one yet. So I retrieved some transistors (F3NK80U, J13009) to amplify the sound from the mp3 player to the speaker. My first questions are :

  • Are those NPN transistors ?
  • Are they suitable for audio ?
  • Are they in TO-220 format and the pins in this order : BCE

I read that the base changes the resistance between the collector and the emitter. So should I connect my mp3 player to the base pin, the 9v battery to the collector and the emittor to the ground ?

Finally, what resistance/capacitance should I use ?


2 Answers 2


In order of the asking, your three quick questions:

  1. From a quick search on alldatasheet.net, the F3NK80 may be a ST made MOSFET, an the J13009 is a Fairchild-made NPN transistor. The last one is along the lines of what you are looking for.
  2. Both could be, the J13009 (NPN transistor) a bit more so than the F3NK80 (MOSFET)
  3. The J13009 NPN transistor is in a B-C-E orientation, as you can see on this datasheet: https://www.fairchildsemi.com/datasheets/FJ/FJP13009.pdf

And to take a step back, I applaud your effort in putting hardware together to learn electronics. But, I think in this case you are going to need to do a bit more reading, because it will take more than a simple connection of that one transistor to make the amplifier you want. It is a bit like cooking - you have some of the ingredients, but you are going to understand a little more about how it works to BOTH select the other ingredients and use them in a way to give you your dish.

This is why some folks use parts like the LM386 - it is an IC that needs little more than a few parts (which they even tell you the values of on the specification sheet), some power, and connections for your input and output, and you will get a very nice amplifier that shouldn't give trouble. Like here: http://www.ti.com/lit/ds/symlink/lm386.pdf

What you are trying to do is build something a bit like the amplifier that is ALREADY built into the LM386 - which is a great little project - but you are either going to need an existing design like this: http://sci-toys.com/scitoys/scitoys/computers/solderless/amplifier.html or http://myplace.frontier.com/~bwalker1945/1QAFAmp.html

Or learn how to design an amplifier for a selected transistor from the datasheet after understanding how a transistor works. There are so many tutorials, here are a couple: http://www.sentex.ca/~mec1995/tutorial/xtor/xtor1/xtor1.html and http://www.techlib.com/electronics/audioamps.html and a common beginners' electronics book: http://www.amazon.com/Getting-Started-Electronics-Forrest-Mims/dp/0945053282

Any way you go, it'll be something you built yourself. Good luck!

  • \$\begingroup\$ There are few designs worse than the single transistor 1W audio amp on sci-toys.com. In the first place, the transistor may be 1W (didn't check), but the power output won't be even close to that. Also the intended half supply voltage at the base won't work with emitter connected to ground. \$\endgroup\$
    – jippie
    Commented Feb 15, 2015 at 9:21
  • \$\begingroup\$ @jippie + one should not drive a speaker with DC offset. And yet also, how that design provides a bidirectional current flow(AC) on the speaker? \$\endgroup\$
    – muyustan
    Commented Dec 11, 2019 at 16:34

I could not find a datasheet for the F3NK80U but here is the J13009. It's a NPN Power Transistor used in switched mode power supplies. It is rated for much higher power than your application. My guess is that it may pull too much current from your battery and drain it more quickly than a typical NPN transistor.

As for the resistance and capacitance values, check out this audio pre-amp from HackaWeek. It uses a 2N3904, a very common NPN transistor and a few resistors and capacitors.


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