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.

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.

Comments

[Ebrahimn]

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]

Hi Ebrahimn,

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

Regards
Milen

[Ebrahimn]

Hi this is how my board looks!

[Milen]

Sorry - the image uploader was not working

[Milen]

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)

[wobbler]

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.

[FuzzyBearGeek]

This is fantastic!, Also, wtg, CrazyG! Geeks are so cool it's ridiculous.

[mightywombat]

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!

[cyber02000]

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]

Hi cyber02000,

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

Regards
Milen

[955josiah]

can i use this as a speaker amplifier???

[Milen]

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

[violator1200]

That's what I call a Macgyver! Awesome Instructable Dood! :D

[pleabargain]

Very interesting. Will be scrounging the flea markets more closely now... btw, typo here: "The sound was quit good..." should be 'quite'.

[Milen]

Thank you for the correction. Now I saw the problem :-). "Lapsus calami" or "Lapsus Keyboard" :-). Good luck in finding the needed toy. Regards Milen

[crazyg]

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!

[Milen]

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]

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]

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]

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

[Milen]

Hi Crazyg, looks interesting... I wish succes. It is interesting to have such kind of toys to play with them... Regards Milen

[crazyg]

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

[shad0w88]

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

[shinigami17]

( - 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]

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...

[Wesley666]

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]

Thanks Wesley666,

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

Regards
Milen

[Wesley666]

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

[jrig]

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

[Milen]

Hi Jrig,
You are right - I use voltage regulator 78L05 which is similar like 7805 but with smaller driving capability - but for this case enough... see step 4

[gnuoy]

Hello milen, great instructable ^^
And I have a question: I dug some old Cd drives here (5 so far) and most of them had a single board with every controller on it, so I thought they wouldn't be very easy to cut/find connections and stuff. But I did find one that only controlled the front of the CD reader. BUT the chip doesn't have a brand, it only says "3543" and I couldn't fin the datasheet for it so far. Since the number is close to the number of the one you showed on the instructable, maybe it works the same way?
I don't have a lot of knowledge on electronics, but I got some tools like a multimeter to test it, and could send you some macro pictures of the board if it'd help; i'm at a loss here ^^'
thanks for the attention!

[Milen]

Hi Gnuoy,

I also was not able to find the chip in the Internet.
It can be some ASIC.
Normally those chips have the same pining as the standard, but it is not always true.
I would suggest the following:
The main task is to find the ground and the supply pins.
Outputs are connected to the phone jack.
The inputs you can find scanning all cable inputs with a signal source through capacitor ~ 10uF.
Usually the ground pin of the chip is connected to the biggest plate on the PCB. Decoupling capacitors between this plate must exist. Their "-" lead is soldered there. Check which chip pin is soldered there. This is "vss".
Check also which other pin has connected capacitor to the ground plate.
This can be the "vdd" (supply) pin.
Try to apply there ~5 V.
Apply signal to the wire of the connection cable and scan all of them.
I hope that you can hear the signal when you touch2 of them.
But have in mind that this instruction will work in the case that the chip has single supply (mostly seen). In the other case it becomes more complicated.
I wish you luck
Milen

P.S. If it didnot work, you can send me macropicture of the PCB - both sides...

[gnuoy]

Hello again ^^
Well, after taking ages to get time to work on it (more so since my laptop stopped working) I got it working today o/
But I tried something different; since the borad was double-sided and there were stuff covering some parts of it, I decided to keep the board as a whole and focused my research on the flat cable that connects it to the main drive. looking it carefully I was able to name the function of 8 out of 13 wires, so I only had to work on the remaining 5; and today I found that 3 of them were supply XP
Lots of thanks, now I just have to search for a casing and some minor details ^^

In case someone wants to know, I used a LG cd reader 52X, and the wiring was like this:
1 and 2  - buttons
3, 8 and 9 - supply (I tried today with 12V, but I think it works on 6V)
4 and 7 - audio input
5 and 6 - ground
10 and 11 - open tray sensor
12 and 13 - motor

[Milen]

Well done Gnuoy!

[telekid]

Hi Milen!!

First, congratulations !! Very nice instructables!! I'm just about to build it up, but I want to know if it's possible to use another energy source..like two AA batteries..does it really need a 9.6v current?

Thanks from Brazil!

[Milen]

Hi Telekid,

I salute Brazil!
I have used 9V battery because I decided to use a linear regulator producing 5V supply voltage and it needs higher input voltage (min. 6.7V ) and the easiest way was to use a 9V battery.
If your amplifier is able to work with voltages ~2.6 V you can use directly 2 AA batteries, for 4V you will need 3 of them...and so.
You can check the minimum supply voltage in the datasheet, when you identify the chip type and find the spec in the Internet.
It is possible to use also boost converter - it will produce high supply voltage for the amplifier based on lower input battery voltage - on the homepage of the National semiconductors ( http://www.national.com ) is placed "Wavebench designer". In the tab "Power" You can enter the input, the output voltage, the desired current and it recommends you which chip can be used. But the circuit is normally complicated and I am not sure how nice the ripples in the generated supply can be filtered in the way that they do not disturb the sound quality. So... my advice - the simplest way to use AA batteries is to connect more of them in series ( min 3 if possible or 4 )

Regards
Milen

[Re-design]

Great work. Very interesting and useful, especially since most of us have half a dozen or so of these laying around doing nothing.

[marc00703]

Awsome 'tables, thanks a lot.

[anand sharma]

how to make a portable guitar amplifier ?

[Milen]

Hi anand sharma,

the amplifier can work also with guitar, but only usung headphones.
If that is not enough for you, look at this instructable:
http://www.instructables.com/id/Portable-Amplifier
or search in internet...
I found the following schematics for you:
http://mycaramplifiers.com/guitar-amp-lm391-189.html
http://freecircuitdiagram.com/2008/11/15/tpa2014d1-low-voltage-class-d-audio-power-amplifier-for-portable-devices/
....
and something realy small and simple:
http://www.redcircuits.com/Page96.htm