How to Make a Pocket Headphone Amp!

In this instructable, I will be showing you how to make a  headphone amp. If you have some big headphones such as Sennheiser, beats by dre or some other big headphones (in my case, some sony MDR-XD100) an or an MP3 player isn't enough, especially if they have a high impedance. This circuit was originally  developed by a man by the name of and it has been extremely popular. There is only one difference with mine (and most others) and that is the fact that he used two single op-amps and we will be using a dual op amp.
So lets get started!



Please don't be too critical, I'm only 14!

Step 1: Parts

Here are the parts you will need:
OPA2134PA op-amp. There are alternatives but I have had most success with this one. The only other one that I would recommend is  OPA2132
1x IC socket
2X 470uf or higher 10V capacitors
2x stereo audio jacks
2x 0.2uf MKT or pollyester capacitors
2X Pannel mount LEDs
1X NPN transistor
1 or 2 9V battery clips
male header pins
1X PCB
1X stereo 10k potentiometer
10k, 100k, 1k, 4.7k, 47ohm resistors (I got packs of 8)
2x SPDT micro switches
3v button cell and holder

A PROJECT ENCLOSURE! Be creative!

Step 2: The POWER Section

Follow the schematic for the power section if you can. 
1. mark a line with a width of 2 holes right down the PCB board. This will be the ground.
2. Solder in the male header pins for + and -
3. Now solder in the Two 4.7k  resistors. 
4. Solder in the 470uf capacitors
5. Look at the diagram (pic 5) and look closely at the "stray" resistor. this is 1k and it's for the power LED
6. try and solder it so it's as compact as possible
In the diagram, the green lines represent the under-board connections. They are usually made with jumpers or solder. In the last picture, I have an example of the under-board connections or "green lines"
Don't worry about the other parts in the last picture, they are for later.

Step 3: The IC Section

Now we are getting into the IC section! this is where the amplification happens.

First we solder in the IC socket for the OPA2134PA. DON't INSERT THE IC YET!
Next we solder two 100k resistors from the ground strip the pins 5 and 3 of the IC socket.
Then we solder in the 1k resistors from the ground strip to pins 2 and 6 of the IC socket
Picture 2 is a pinnout diagram for the pins.
Now solder in the 0.2uf capacitors. Solder one pin of the capacitors to the 100K resistors (pins 5 and 2)
Solder the 10k resistors, like the capacitors to the 100k resistors, to the end of the 1k resistors.
Now solder the 47Ohm resistors to pins 1 and 7. 
Now connect the ends of the 47ohm and the 10k resistors
Now at header pins to the connected ends of the 10k and 47ohm resistors and the other end of the capacitor.
Now it should look like picture 8
The last step for this section would have to be to connect the power supply to the op-amp. The + connection will go to pin 8 and the - voltage connection will go to pin 4

All done on the circuit!

Step 4: The LED Flasher Circuit

This is the LED flasher end of the circuit. Follow the circuit diagram and if you want more details on the circuit, look at my ultimate LED guide. This is almost self explanatory as I have explained this in the Guide. How you integrate it is totally up to you. If you do it on PCB, use header pins for the outputs to the LED.

Step 5: Wiring Everything Up

I've included two pictures to help you wire the potentiometers for volume control. Wire up the power LED and the light flasher LED once they have been mounted in the case.. The positive output from the LED flasher circuit will go into one of the switches and from the output of the switch to the LED. I also have a picture on the pinnout of the 3.5mm stereo jack. Now wire up power, all ground connections together and all signal wiring. Here is a signal diagram:
Jack L+R  ⇒⇒ Potentiometer L+R ⇒⇒Audio in L+R ⇒⇒ Audio out L+R ⇒⇒ Jack L+R
Make sure all solder connections are good

Step 6: Close Up the Case

Finnish everything  up and test to make sure it's ok. If it's all good, close up the case

Step 7: Finished!

All done!. Enjoy your headphone amp!

If you find this instructable insufficient to build a headphone amp, LET ME KNOW so I can improve it. 
If you have and problems, head over to here to troubleshoot. 


ENJOY!

Step 8: Video

I have a video of my other headphone amp here

Comments

[brunowpsouza]

Hi there. Your preamp is good and simple enough for my needs. Thank you very much.

However I need to make sure of the input impedance upfront for a better choice of possible instruments to hook up to your headphone preamp. I dont intend to do much, but connecting a mic to it for practice.

Is it possible?


All the best.

[brunowpsouza]

I forgot to mention. I will make use of the 5$ microphone preamp available on the website, as follows:

https://www.instructables.com/id/Build-The-5-Microphone-Preamp/

The connections diagram would be like this:

Microphone > 5$ mic preamp > pocket headphone preamp> headphone



All the best.

[mjfutures]

Will this work for ear buds or do I need to make modifications?

[ZackS54]

Earbuds will work just fine. Earbuds work the exact same as headphones do on the inside, so the electronics don't need to be changed at all. The only difference between headphones and earbuds is the size (and to some extent, the sound quality as a result of the smaller size). I would recommend getting a higher quality pair of earbuds to really use this to its real potential, try Googling "In-Ear Monitors" instead of "earbuds" and the results will be much better, and prices tend to be more reasonable for the sound quality than most big name earbuds.

[Age DiazM]

hi there!

i think you had a good idea for my spare time.
So i want to ask you,can i change the power source to lithium or 18650 battery?
thanks.

[EliasC39]

Hi i just saw your question and thought that i would help you so i checked the datasheet and the min. Input voltage is 2.5v and the avereage output voltage of a lithium-ion/lithium-polymer/18650 battery is 3.7v so it should work but the amplification can be a little bit lower than with a 4.5v power source.

(please note that you would need a Tp4056 charger with overcharge and overdischarge protection)

Here is a link for a charger with overcharge and overdischarge protection:https://m.aliexpress.com/item/32453058256.html?pid=808_0000_0101&spm=a2g0n.search-amp.list.32453058256&aff_trace_key=f93d4917566146c1b979c408edb5d22a-1547494025466-02837-aAU3zrB&aff_platform=msite&m_page_id=1317amp-9pbgt1pVS3r0fRTz-OX47g1548528069100

Here is the schematic for the modified circuit.
(please tell me if it worked or did not work. If it did not work i will try to help you as much as I can)

[EliasC39]

Oh sorry i forgot to draw that pin 4 goes to - / 0v

[sdhar5]

Can i use bc54u transistor

[sastrys1]

hi I tried this and it works nice.

now I want to have a bass and treble controls on my device so please tell me how to add those controls and also post a schematic.

[bilden]

People #%#&HEY WAKEUP ;). Start reading threads before posting.

[chillrov]

sir can i have a clear schematic please?

[dog digger]

Schematics are available from tangentsoft and here's a link from their site: http://tangentsoft.net/audio/cmoy/misc/cmoy-tangent-sch.pdf

[rotem]

how do i make the left channel and the right channel to one 3.5 mm connector

i mean how do i connect it to 3.5 mm jack and make it stereo

[dog digger]

On the stereo connector, you should have 3 pins. Left, Right and ground. If yours only has 2, then you have a mono connector

[nkhoo]

Can you explain what the header pins are for? I apologise for my inexperience but i am very blur. Any explanation would be greatly welcome. Thank you in advance

[dog digger]

Sorry for the very late reply but I used them because they make it easier to solder wire to the PCB so if something goes wrong, it's easier to troubleshoot

[digitalfear83]

can you draw up a diagram of the circuit and send it to me

[mdog93]

Will ANY NPN transistor work? What criteria does it need?

[agm88]

oh and an s9014c transister is pre amp low noise and low level transister
but i would rather use a bc548 for the LED synce

[agm88]

any NPN general purpose transister will work like for example
2n2222a
2n3904
2n4401 works quite well
and bc548 which is eqivalent to a 2n3904