Instructables

Headphone amplifier

This instructable describes how to "make" a simple audio headphone amplifier.
It can be used with different devices - MP3 players, Walkmans, Radios, .etc. It can be used also for your own designs - can be connected to the analog outputs of audio DACs, to the outputs of self made radios (for example using TDA7000, or TA7642) or other gadgets.
In comparison with the other instructables, this will not give you an exact instructions how to do the job, but will give you the idea and show you for example how it can be realized in a particular case. The success of this project will relay on your imagination and capabilities ...

The main idea here is - why to make something from scratch, if it exists...
Where an existing audio amplifier can be taken from?
The answer is - from a defect computer CD-R,W, DVD-R,W reader, writer, ROM-drive..
All they have audio output for headphones, which has almost always a volume control.
When those devices broke, normally the malfunction is always in the mechanics, in the laser system, in the optics, but, I think never in the audio headphone amplifier.
Where to find a defect drive?
You decide - at scrapyard, at the place were you company throws away the broken equipment for recycling, in some garage sale, to ask your friends, eBay...

Let's suppose, we have found our defected drive.
Let's go for the first step.
 
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Step 1: Exctracting the audio amplifier board

First step is to disassemble the drive.
The audio amplifier board is normally placed directly behind the front panel of the drive. The PCB in most cases has a long narrow shape. Between the audio amplifier board and the "main" board of the drive a flat cable connection is done. Unsolder it from the main board. May be will be possible to use it, if needed.
Do not forget to extract also the laser diodes and the electric motors - they can be used for other instructables.
On the pictures can be seen the extracted board, which was placed behind the front panel and contains the audio amplifier.
demonas made it!1 month ago

Great idea and exactly what I was looking for :) Had my headphones connected directly to my PS3's RCA outs and it was a bit lacking in volume so this is perfect. The PCB I had even seems to be almost identical to the OP's as far as component placement goes :)

CAM00014.jpgCAM00016.jpg
Milen (author)  demonas1 month ago

Hi,

Thanks :-)

Only as a warning...

If you look the previous comments, you will find that this topic was discussed once -the OPA3541 practically act as buffer - you will not have increase in the voltage gain, but if your output stage has high output resistance, and can not drive well the low resistive load, then the improvement will exist.

If you want to have also voltage gain - than you have to look for another board, where real OpAmp is used (or Headphone amplifier special chip) and there you can try also to change the feedback resistors and to increase the voltage gain....

But in all cases, the fun remains :-)

demonas Milen1 month ago

Thanks for the advice, I'll be aware of that. Maybe there's any cheap and decent chips you could recomend? OPA132 are hard to find here and quite expensive. I've tried making an amp with a TDA2822 but the results were underwhelming, ofcourse it was on a protoboard rather than a proper PCB but the amount of noise was definitely an issue. I should probably come back to it and put some resistors on the output to reduce the noise, maybe redo the board aswell. Kinda ditched the TDA after powering it up the first time.

Milen (author)  demonas1 month ago

Hi,

You could try with LM4880M (see my other instructable : http://www.instructables.com/id/Audio-mixer/ )

I have seen CD/DVD boards with APA2308, where you can change the feedback resistors.

There also a lot of other dedicated chips :

From TI: http://www.ti.com/lsds/ti/audio-ic/headphone-ampli...

From Maxim : http://para.maximintegrated.com/search.mvp?fam=hdp...

From STM : http://www.st.com/web/en/catalog/sense_power/CL150...

etc...

The easiest solution would be to use amplifier with limited number external components. There are few from TI, which require only few capacitors. Another interesting solution could be to use class D amplifier - they also require limited number external devices. If you want to try on a breadboard, better to use DIP package. All of the listed companies provide free samples - you can try to order...:-)

hippydog6 months ago
A little involved but a great way to recycle all the old computer CD drives..
thanx!
Milen (author) 7 months ago
Hi,

It seems that the output stage is realized by the use of the JRC opamp NMJ3414A (IC501). I have marked the place where I think the output stage should be. Using Ohmmeter you can track the input paths and the supply lines of the power opamp and limit the area only to needed parts. The neighbor big chip is Mitsubisshi M63020 motor driver chip, so I think it will be easy to distinct which R,C device, which of both chips support. Good luck.
F2EBP01HLFUXGGA.jpgnjm3414a.JPG
Bogdi7 months ago
Hello, i ended up with this kind of board and i dont know single thing of what is going on there.

2a.jpg1a.jpg1b.jpg2b.jpg
elbotho1 year ago
Perfect!
I used an old DVD drive for the laser and now I could also use it to build a headphone amp. Thank you very much! I checked with the datasheet and the multimeter and the pins on the flat cable were next to each other:
[?] [5V] [GND] [in1] [in2] [...]
casey321b1 year ago
I had just taken apart a CD drive for the motors. I'll attempt to try this soon. Looks great.
Mr.Gizmo1 year ago
I copied this project perfectly. The circuit board was even identical off an old cd rom I had laying around. I can truly say the sound is the same with or without the so called amp. Sorry to burst your bubble but after doing some hard research I came to find that this IC chip is simply an audio driver its not an OPA amp IC. Waste of time. Should have researched first!
Milen (author)  Mr.Gizmo1 year ago
Hi Gizmo,

As I wrote :

"This instructable describes how to "make" a simple audio headphone amplifier.
It can be used with different devices - MP3 players, Walkmans, Radios, .etc. It can be used also for your own designs - can be connected to the analog outputs of audio DACs, to the outputs of self made radios (for example using TDA7000, or TA7642) or other gadgets.
In comparison with the other instructables, this will not give you an exact instructions how to do the job, but will give you the idea and show you for example how it can be realized in a particular case. The success of this project will relay on your imagination and capabilities ..".

I want to give only an idea how to do the amplifier, without saying that exactly this type of opamp must be used.
Ofcourse, if your CD ROM has a driver chip inside, you can use it only as buffer to some audio DAC or chip without output stage.

If you want to have real amplifier - than you have to find such kind of pcb.
May be you can even change the feedback resistors in the way that you have the gain that you want.

And finaly, I do not think that the hoby activities are lost of time.
It is way of learning...

Best Regards
Milen
Ebrahimn2 years ago
I want to make a mini amp and have all the chip on the board, but it is a full board and not the strip that is shown on your design. How do I indentify wher the cut line should be.
Milen (author)  Ebrahimn2 years ago
Hi Ebrahimn,

It is diffucult to say.
can you publish a photos of the pcb taken from the both sides?

Regards
Milen
Ebrahimn Milen2 years ago
Hi this is how my board looks!
MINI AMP 002.jpg
Milen (author)  Ebrahimn2 years ago
Sorry - the image uploader was not working
F82IVIBH045XCLU_SMALL.jpg
Milen (author)  Ebrahimn2 years ago
It is difficult to say, but i think somewhere here.
You have to know which is the audio chip. I thnik they use alos 7805 or some similar chip there (the 3 pin one). You have to decide - shall you use it also fro the supply of the audio, or you will use some batteries.
Find the inputs for the audio signal - may be they are close to the volume control potentiometer. Practically you have to have around 4-6 connections from the PCB which you cut - the inputs, GND - the biggest area plate, supply, and may be some controls (for LED, mute...etc)
wobbler2 years ago
I like the idea- these are ten a penny on car boots and I've been thinking of making something similar for my guitar.

As the specs for the PSU voltage are 3-6v (typically 5v) you could make the project simpler by using three AA/AAA baterries to run this and cut out the regulator. You might even get away with just two batteries. This would mean you are not having to bother with making up the voltage dropper bit, AA/AAA batteries are cheaper than 9v ones and last longer and in addition you are not wasting power in the voltage dropper so they should effectively last even longer. Three AAAs wouldn't be much bigger either.

I'll get one and try it.
This is fantastic!, Also, wtg, CrazyG! Geeks are so cool it's ridiculous.
Bril, mate! I was taking apart a CD drive the other day and saw the amp in it and that got me thinking of doing exactly this. Thanks for the great instructable!
cyber020003 years ago
hey ...!! great instructable it got me started the moment i saw it.....but i am having a little problem.....not to be offensive in any way but their are some steps missing....or maybe because i am a total noob and dont get the figure it yourself part
Milen (author)  cyber020003 years ago
Hi cyber02000,

If you do not understand something, do not hesitate to ask me. I will try to answer all your questions.

Regards
Milen
955josiah3 years ago
can i use this as a speaker amplifier???
Milen (author)  955josiah3 years ago
Hi 955josiah,

It denends on the amplifier chip and the load resistance of the speaker.
The chip used in this design can drive ~140mW in load 16 Ohm.
Normally the speakers have 4 or 8 Ohm resistance. May be exist also with 16 Ohm...
If you connect only 8 Ohm you can reach more power, but you can overheat and burn the chip. May be if you connect two 8 Ohm speakers in series for a channel - will be OK. Once again - it depends on the chip!

If you use active speakres (PC) - there is not any problem!
The other posible solution - to make additional simple amplifier.
For example two transistors NPN and PNP connected as emitter followers - you can find circuits in the net...

Regards
Milen
That's what I call a Macgyver! Awesome Instructable Dood! :D
pleabargain3 years ago
Very interesting. Will be scrounging the flea markets more closely now... btw, typo here: "The sound was quit good..." should be 'quite'.
Milen (author)  pleabargain3 years ago
Thank you for the correction. Now I saw the problem :-). "Lapsus calami" or "Lapsus Keyboard" :-). Good luck in finding the needed toy. Regards Milen
crazyg3 years ago
THANKS 4 tha idea (how olds yr circuit board i mean like there are proper sized components on there ) heres my first pic of progress so far, luckily our chips are more or less the same so i used your diag, ground is occuring through game boy at moment, though getting some strange eerie sounds at low volume i think its 7 colour changing leds/backlight and pitchbender in the gb causing this!
DSCF1237.JPGDSCF1236.JPGDSCF1235.JPGDSCF1235.JPG
Milen (author)  crazyg3 years ago
Hi Crazyg, What I see om your pictures is that you apply the input signal directly at the potentiometer pins. Am I correct? It is possible that you have DC connection in the signal path. You have to be sure in which configuration the amp works.Try to apply the input signal through capacitors - I see, there are some around the chip..., or you can use some external- may be this will help. It is possible that the LEDs cause the problem - try with some power source instead the batteries - if it works without the problems - this can explain the cause of the strange behaviour. Regards Milen
crazyg Milen3 years ago
hey, i didnt mint the background noise,but now iv cut what i thought was all the vital bit of the board out that noise is all iv got,so iv got more guessing to do. since your there,do you know how to boost the output volume up a bit?
Milen (author)  crazyg3 years ago
Hi Crazyg, I see that you use a fixed load - I suppose that you will not go to change some feedback resistors for the opamp to increase the gain. May be the only way ist to increase the supply voltage of the opamp... but be careful with that - not to burn the chip... Regards Milen
crazyg Milen3 years ago
hi milen..fixed load?,,,erm im putting about 6v in at moment maybe a bit less as the gameboy has got a v regulator in there somewhere(weather active in this config i ??havent mesured it) the connections im using at the moment (test stage) are the neg from the prosound output and the pos direct to the battery, when its wired propley gonna use the same pos as the pitch bender(i think its off the volt regulator board) then it wont have power when gb is off, and the neg from the signal (less wire to cram) as for changing resistors there a bit dinky on this board ,was planning to use a velleman kit* for this job but its still in the post!(continued gratitude for your structable)as are a couple of switches im planning on putting in the gameboy(want to put the rest of the components in in one go as its getting tight in there) as for this board its allready glued into a cut down camcorder tape box with little speakers superglued in added off switch for speaker output(i hate it when that glue leavs its white residue) then ill stick the box on the back as shown ,result..game boy with stereo speakers,(the original speaker and headphone stopped working long ago tried replacing speaker no result)headphone out,line out,backlight,pitch bend(goint to be switchable)and wonky ziggy lighting,.:) *got any more detail on boosting the output of these circuits?will have a better idea when the velleman arrives hopefully. here are the latest pics ,all the best from george
DSCF1250.gifDSCF1251.gifDSCF1252.gifDSCF1255.gif
Milen (author)  crazyg3 years ago
Hi Crazyg, looks interesting... I wish succes. It is interesting to have such kind of toys to play with them... Regards Milen
crazyg crazyg3 years ago
yep i used the pot contacts as iv been prosounding gameboys and it works for them,here are some better pics.still trying to figure out what iv broken....whilst loading photos, found if i apply power to pin 2 (second one down on left next to one with spot,incase my number system is wrong) so now i can loose another1.5cm off the width of the thing woohoo
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shad0w884 years ago
i have g1401 amplifier with following datasheet... which terminals are for the input.. i'm confused coz it has 3=input a pos 2=input a neg 5=input b pos 6=input b neg
here's the datasheet
http://www.datasheet4u.com/html/G/1/4/G1401_GlobalMixed-modeTechnology.pdf.html..

please help
( - input A 2) +(  + input A 3) = output A 1 or first speaker
( + input B 5) + ( - input B 6) = output B 7 or second speaker
4 is negative supply
8 is positive supply



Milen (author)  shad0w884 years ago
Hi saad.dawra, I saw the datasheet - the chip contains 2 OpAmps. Each OpAmps has 2 inputs - inverting and not inverting - depends on the configuration - inverting or not inverting - the inputs should be different for noniverting configuration - inputs should be 3 and 5 for inverting 6 and 2. You can try to identify which type of configuration you have... But I will propose a different, more simple way to identify the PCB inputs of the flat cable. Take a signal source (some voltmeters have embedded signal generator), MP3 player or radio - connect the ground cable of the signal source to the ground of the PCB, and through capacitor 10 uF apply the signal to every input (solding pad) - simply scan all of them. Of course the OpAmp must be supplied and headphones must be connected - I hope you will here the sound scanning all the inputs - for the right and left channel. Then - simply audio connect you cable to this pads. Do not forget, during the test to turn the volume regulator wheel in the way that you have some acceptable level of amplifying. Good luck with the experiments...
Wesley6664 years ago
This is awesome!  I never thought something like this would work!  But you shown me it has!  I gotta try this!  Been wanting to build an audio headphone amp for awhile.  I hate using IC's though, I consider it cheating...

Great Instructable though!
Milen (author)  Wesley6664 years ago
Thanks Wesley666,

you are right - it should work if everything is done right...
About the ICś - I would like to advice you ...to use them   :-)
They make the life easier...

Regards
Milen
Wesley666 Milen4 years ago
I do use them on larger circuits where the circuit  board would be overflowing if I didn't.  Smaller circuits though, I like not using them because usually you can get the same thing done with a few more parts with not using an IC, because sometimes you don't have the exact IC on hand.  Its kinda a bike light, why would you use a 555 timer when you can use the dual LED flasher circuit and have it flash one LED up front and one LED on the back of the bike and the circuit is no larger.  But they do make life easier on some bigger projects!

Thanks
jrig4 years ago
i think the maximum input voltage is 5 volt! you'd better using a voltage regulator (7805)
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