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http://www.instructables.com/id/Headphone-amplifier/ Home Sign Up! Explore Community Submit All Art Craft Food Games Green Home Kids Life Music Offbeat Outdoors Pets Photo Ride Science Tech Headphone amplifier by Milen on April 30, 2009 Table of Contents License: Public Domain Dedication (pd) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Intro: Headphone amplifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 step 1: Exctracting the audio amplifier board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 step 2: Shaping the amplifier board. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 step 3: The research work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 step 4: Power supply connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 step 5: Connecting the mute signal. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 step 6: Connecting the LED as power indicator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 step 7: Connecting the inputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 step 8: The joy... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Related Instructables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Advertisements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Comments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Headphone Amplifier

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Headphone amplifierby Milen on April 30, 2009

Table of Contents

License:   Public Domain Dedication (pd) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Intro:   Headphone amplifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

step 1:   Exctracting the audio amplifier board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

step 2:   Shaping the amplifier board. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

step 3:   The research work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

step 4:   Power supply connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

step 5:   Connecting the mute signal. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

step 6:   Connecting the LED as power indicator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

step 7:   Connecting the inputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

step 8:   The joy... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Related Instructables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Advertisements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Comments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

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License:   Public Domain Dedication (pd)

Intro:  Headphone amplifierThis instructable describes how to "make" a simple audio headphone amplifier. It can be used with different devices - MP3 players, Walkmans, Radios, .etc. It can beused 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) orother 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 forexample 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 makesomething 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 themechanics, 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 placewere 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 boardFirst 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 narrowshape. 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 touse 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 theextracted board, which was placed behind the front panel and contains the audio amplifier.

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Image Notes1. The Audio output for the headphones2. The volume control

Image Notes1. Skrews to be removed2. Another skrews to be removed

Image Notes1. The extracted PCB containing the audio amplifier

step 2: Shaping the amplifier board.The second step is to investigate what you have. It is good practice to take a picture of the board by a digital camera in macro modus, to plot it, if possible on A3 sheet,and to try to understand the structure of the board. You can see that also some additional electric components are placed on the board - switches, LED's for read/writeoperations.. etc. You have to decide what should be used - do you need light indication of the supply presence, do you need the volume control.. Normally, for the lownoise reasons, the audio amplifier occupies a compact area, which must be identified. In this case it is about 1/3 of the whole PCB area placed at the end of the boardwhere the chip is mounted. The next action is to mark the part of the board which should be used, in the way that the signal paths and supply for the audio amp tracksshould be kept safe. There are always some tracks which connect switches, sensors, LED's placed on the other part of the board and can be cut without any influence onthe audio amp performance. For the marking I used a dark marker. Now the board can be cut. For that purpose I use usual scissors. You have to cut the board carefullysome distance away from the marker line - because of the cracks, which appear during the cut. After cutting the board, it must be shaped - all sharp edges have to bepolished. For that purpose an abrasive paper can be used.

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Image Notes1. The cut line

Image Notes1. Abrasive paper2. This side to be polished also

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Image Notes1. The LED - I decided to use it for Power indicator2. The chip3. The volume control4. Audio stereo jack5. Flat cable - can be used, but I decided to remove it

step 3: The research workNow starts the real research work. We have to identify which chip is used for the audio amplifier, to find the technical data (the datasheet), and to track all connections. Inthis case it is easy to see that the chip is from the type APA3541 (product of ANPEC - http://www.anpec.com.tw ). Using the "Google" the datasheet can be found veryeasy. The APA3541/4 is an integrated class AB stereo headphone driver contained in an SO-8 or a DIP-8 plastic package with Mute feature . For us the most interestinginformation, found in the datasheet is : 1)the block diagram with the function pin description ;2) the typical supply voltage -for this case it is 5V ; 3) the possible driven load(can be 16 Ohm).

The task is now to connect the amplifier in the correct way.I removed the flat cable. I plotted the picture of the PCB with the metal tracks view on a A3 sheet - to be easy to follow each track and connection. You can use markerswith different color for each signal.Let's start with the ground pin - normally the ground is the "fattest" wire on the PCB. It is chip pin #4.Using Ohmmeter you can check this. A suitable place where theground cable ( "-" of the battery) shall be soldered must be found. There the green lack must removed from the PCB. I scratch it using a big needle. A hole for the groundcable must be drilled there.

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Image Notes1. APA3541 - The pins are numbered on the PCB

Image Notes1. The typical supply voltage2. You can drive 16 OHm load

Image Notes1. To be plotted on a big sheet.

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Image Notes1. pin #42. Ground PCB contact3. Zero resistance

Image Notes1. Drilling a hole for the ground cable

Image Notes1. Here the ground cable will be soldered

step 4: Power supply connectionNext step is to guarantee the proper power supply of the chip. We found that the chip must be supplied by 5V source. Such kind of batteries are not often seen. It is betterto use a voltage regulator , which will produce the needed voltage. The most suitable, I found to be a regulator from the type 78L05 - it has 3 pins and small package.Practically it doesn't need an external components. To mount it on the PCB we need to scratch the green lack again in the proper places and to drill 3 holes for its pins.After that we can mount the regulator, solder it and to bridge the ground line.

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Image Notes1. Here will be the ground connection2. Will be used as bridge for the ground connection3. Floating tracks - can be used for the ground connection also4. Here will be soldered the regulators ground pin5. Here will be the input pin of the regulator6. Here will be the Power supply cable coming from the battery7. The output of the regulator8. small resitor in the power supply chain9. Power supply pin of the audio amplifier chip

Image Notes1. The holes for the regulator, the "+"cable, and additional hole to cut the supplytrack coming from the pads of the flat cable

Image Notes1. The ground bridge

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Image Notes1. The mounted 78L05 regulator

step 5: Connecting the mute signal.In the datasheet was seen that the audio amp has a mute pin - your decision : You can have a switch to mute the amplifier, or to connect the pin hard to the supply linefor continuous operation. I connected it directly to supply line.

Image Notes1. The mute signal connection will be done at this place

Image Notes1. The connection

step 6: Connecting the LED as power indicatorBecause of the existing LED - I decided to connect it as power indicator. Two connection must be done for that purpose : - the resistor limiting the current through theLED must be connected to the supply line - the cathode of the LED must be connected to the ground line

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Image Notes1. The LED cathode connected to the ground2. Current limiting resistor of the LED3. Connection of the LED chain to the supply line

step 7: Connecting the inputsNow remains to connect the inputs of the amplifier. I used a cable of defected stereo phones. Depending on the way of use of the amplifier, different cable connectionscan be implemented. Following the input tracks using the ohmmeter (the inputs of the audio amp chip are connected to the volume control potentiometer, after thatthrough electrolyte capacitors ) I identified the pads for the flat cable where the input signals come. Two holes for the left and right audio signals and an additional hole forthe ground cable wire were done there.The audio and the power supply cables were soldered.In the case, you want to connect the amplifier to a mono audio signalsource, it is better to short the both inputs together.

Image Notes1. Holes for the audio inputs2. Hole for the ground wire of the audio cable3. The soldered ground battery cable

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step 8: The joy...It is good to find a suitable box for the amplifier and the battery. It can be plastic or metal - in the second case an insulation must be put between the internal walls of thebox and the PCB, to prevent a short. A hole for the volume control must be cut. I used a plastic box suitable for small radio, where a special place for the 9V ( 6LR61type)battery was reserved. I added an ON/OFF micro switch at the cable from the battery "+". I cut a holes on the box side wall for the volume control, for the audio jack, forthe LED and for the micro switch knob using a dremel like tool. Finally I fixed the board using 3 small screws. I connected the battery, switched the amplifier on..... Thesound was quit good... Enjoy, you too!

Image Notes1. The amplifier in operation...

Image Notes1. ON/OFF switch added2. Holes for the LED, the volume control wheel and the stereo jack cut

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Image Notes1. The ON/OFF micro switch

Image Notes1. The volume control

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Comments21 comments Add Comment

 admin says:  May 4, 2009. 11:31 AM  REPLYThis is a great Instructable, but you need to add a main image of the final project to the intro step. Please do that and leave me a message when you haveso that we can publish your work.

Thanks!

 gnuoy says:  Oct 29, 2009. 5:56 PM  REPLYHello milen, great instructableAnd 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 bevery 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 thesame 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'dhelp; i'm at a loss here 'thanks for the attention!

 Milen says:  Oct 30, 2009. 1:05 AM  REPLYHi 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 issoldered 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 luckMilen

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

 telekid says:  Oct 21, 2009. 6:51 AM  REPLYHi 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 twoAA batteries..does it really need a 9.6v current?

Thanks from Brazil!

 Milen says:  Oct 21, 2009. 10:13 AM  REPLYHi 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 theeasiest 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.

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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 ofthe 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 thegenerated 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 connectmore of them in series ( min 3 if possible or 4 )

RegardsMilen

 saad.dawra says:  Aug 30, 2009. 7:17 PM  REPLYi 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 pos6=input b neghere's the datasheethttp://www.datasheet4u.com/html/G/1/4/G1401_GlobalMixed-modeTechnology.pdf.html..

please help

 Milen says:  Aug 31, 2009. 1:24 AM  REPLYHi 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 ornot inverting - the inputs should be differentfor noniverting configuration - inputs should be 3 and 5for 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 signalgenerator), 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 toevery 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 thesound 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 thevolume regulator wheel in the way that you have some acceptable level of amplifying. Good luck with the experiments...

 Re-design says:  Aug 20, 2009. 5:32 AM  REPLYGreat work. Very interesting and useful, especially since most of us have half a dozen or so of these laying around doing nothing.

 marc00703 says:  Aug 17, 2009. 1:26 AM  REPLYAwsome 'tables, thanks a lot.

 anand sharma says:  Aug 13, 2009. 8:48 PM  REPLYhow to make a portable guitar amplifier ?

 Milen says:  Aug 14, 2009. 9:13 AM  REPLYHi 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-Amplifieror search in internet...I found the following schematics for you:http://mycaramplifiers.com/guitar-amp-lm391-189.htmlhttp://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

 y001 says:  Jul 11, 2009. 4:57 AM  REPLYOh! Good iDEA

 wsx587 says:  Jun 25, 2009. 7:53 PM  REPLYwhere do u plug in ur mp3

 Milen says:  Jun 26, 2009. 1:58 AM  REPLYThe stereo audio jack (the picture from the 7th step) is the input of the amplifier, which must be plugged in the mp3 player phones jack.

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 lisaf82168 says:  May 10, 2009. 8:59 AM  REPLYThe board I got out of my cdrom has the ribbon cable on the opposite side away from the headphone jack and amp circuit. I'm just starting to look at it, butdo you think this means I won't be able to cut the board down? Thanks.

 Milen says:  May 11, 2009. 12:06 AM  REPLYHi lisaf82168,I am not sure before I have seen thw PCB, but I think that it can be possible to cut the board - after that you have to track the connections from the chippins, to make holes in the proper paces and to solder all needed cables there. It is not necessary that the connections are done where the ribbon cable issoldered - better solution to wire them as close as possible to the amplifier.I wishh you success.

Milen

 lisaf82168 says:  May 11, 2009. 4:05 PM  REPLYThanks for your help. I started thinking the same thing after I asked the question.

 Milen says:  May 12, 2009. 12:12 AM  REPLYYou are wellcome..

 DanAdamKOF says:  May 5, 2009. 3:34 AM  REPLYThis is awesome, dead and discarded CDROM drives are everywhere. I wonder how this competes with a Chu Moy amp and similar.

 Milen says:  May 5, 2009. 4:27 AM  REPLYHi DanAdamKOF,

I tool a look at Chu Moy amplifier - it is almost the same - in the project is used also a power OpAmp. In this case also, but , you have to have in mindthat in the different drives different chips will be used - I have mostly seen those from National Semiconductors - dedicated headphone amplifiers. Themain challenge is to find the datasheet, to "decode" the connections, to apply the proper supply and load, and to wire connections in the correct way.And, it will always work (99%) :-). The advantage in this approach is that you have all components mounted, it is pay less, and the result is the same asselfmade amp, starting from scratch...

Regards

Milen

 Milen says:  May 4, 2009. 1:12 PM  REPLYHi admin,

I added the main image to the intro step.Have a nice day!

Regards

milen