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Op-amp headphone amplifier

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Picture of Op-amp headphone amplifier
This is a headphone amplifier similiar to the one designed by Chu Moy. For reference, the original Chu Moy article is here while a great tutorial on building it is here. I have used a different dual operational amplifier, the RC4560, manufactured by Texas Instruments, in the TSSOP package, and chip resistors in order to make an extremely small printed circuit board assembly.
 
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Step 1: The op Amp

Picture of The op Amp
The active device is the RC4560, which Texas Instruments claim to be suitable for, among others, Headphone amplifiers. It can work down to +/- 2 volts, and has low noise and a wide enough bandwidth.

It is available in a TSSOP (Thin Shrink Small Outline Package) which means it is small indeed, small enough for me to demonstrate my one-off microprototyping skills.

Step 2: The circuit

Picture of The circuit
The circuit is the standard non-inverting amplifier with a gain of 11, with a capacitively coupled input. A small valued resistor at the output of the amplifier isolates the load and minimises any tendency of oscillation with long headphone leads.

The large size of the input capacitors make them too bulky to be included on board, so they shall be outside, between the input jack and volume control, and the board.

The power supply is provided by a nine volt battery, converted to dual +/- 4.5 volts by 4.7K resistors and decoupled by 220 microfarad capacitors.

A high efficiency Light Emitting Diode shall provide indication that the circuit is ON, it is fed with about 0.7 milliamperes by a 10K resistor.

Step 3: The components

Picture of The components
The picture shows the integrated circuit and resistors. The chip is a free sample from Texas Instruments, and the resistors are all scrounged from old hard drives. The four digit marking means they are all of 1% tolerance, and they might even be MFR (metal film resistor). There is absolutely no way to confirm this, however.

The small size of these components make it very difficult for conventional point to point wiring techniques to be used. In fact the only viable means of connecting them up is to use a printed circuit board.
SharpyWarpy6 months ago
The RC4560 is a bipolar input op amp. Unless you use caps on the output it's going to pose problems with DC offset voltages, which can destroy headphones. It provides great current though. I realize this is an old instructable but I had to say something.
sconner11 year ago
Change the 220 uF caps to 470uF for better bass response and more powerful drums. You'll be hooked and have to re-listen to your whole music collection to hear what you have been missing.
And get some over the ear headphones.
The beauty of headphone amps is lost on "buds".
sconner11 year ago
1% resistors are usually metal film.
Bonus points for recycling/frugality.
gulshan203 years ago
sorry for this stupid question,but why do you use capacitors at the inputs?
is the voltage IN always constant?if not,then why did u put it in there?
sorry,i am a college student.
thanks for the reply.
btw,very good project:)
They filter out any DC offset in the input signal by blocking DC and allowing AC (audio) to pass.
Otherwise you risk burning out your headphones with amplified DC output.
He's using the caps to filter the input signal and get rid of any DC component, to not mess with the bias of the amp. Caps are not just for transients, they are used for a lot more.
gjvg2 years ago
in the top left schematic i see a ground sign... where do i connect it to?
And is it a problem if i use a 47 ohm resistor instead of a 50 ohm resistor?
sconner1 gjvg1 year ago
That is input signal ground.
Also called shield ground in the signal cable context.
This is really quite awesome and amazing.

So I have a pair of OLD headphones with huge speakers. My plan is to replace the old speakers with new 2.5" powerful speakers and to somehow throw a powered amp in there to basically make headphones that when safely removed from the head, could blow my friends away with sound. I figured I could cram at least 1000Ah of power source and can easily fit 80+ watt speakers in there. I'm a novice electrical hobbiest.

Any ideas?

Thanks a ton.
Eng.A.S.M3 years ago
(removed by author or community request)
neelandan (author)  Eng.A.S.M3 years ago
The sweetest things in this world are made by hand.
Sandisk1duo5 years ago
do you think i can make this without any resistors?
y would u want to make it without resistors anyway?
neelandan (author)  Sandisk1duo5 years ago
No.
how about the capacitors on the inputs? inL inR
neelandan (author)  Sandisk1duo5 years ago
They may be omitted in most cases. They are needed only when the input signal has a direct voltage component (ie, direct coupled single ended transistor stage without an output capacitor). You can try building one without the input capacitors, and then put them in if the output seems to clip. The low frequency response will be better without them in circuit.
LiporXT4 years ago
hello Neelandan I find your instructables really small and cute, congratulations. I have a question: can operate the amplifier with an integrated 3414th jrc? if so, how? thank.. Ps:sorry for the bad english I'm italian..
Re-design4 years ago
Hey, I'd build one of these but it's just too darn big. I need something really small and this one's big as a horse. Not really! Great job. I've built my own boards but never a surface mount! Hope you never drop it on the floor you might not be able to find it.
Meigus5 years ago
Doesn't your circuit only have the capacity for one channel? If I'm not mistaken, this would be a mono headphone amplifier.
neelandan (author)  Meigus5 years ago
The chip I used has two op amps in one package, which shares the supply pins. Therefore this is a stereo amp.
Man, I woulda used a 386 IC That's my favorite chip for the matter.
386 OP AMP
http://www.flashicon.net/archives/LM386Pinout.jpg
BTW add heatshrink tubing for stability.
friendspore6 years ago
Another site that teach step by step for building cmoy for beginner
http://williamneo.blogspot.com/2008/01/diy-cmoy-headphone-amplifier-for.html
happy building!
Nirjuana6 years ago
You done some nice modification in to the original Cmoy circuit but I recommend to use some different kind of power source cos' capacitor-voltage divider has one problem, it gets very easily unbalanced and that means that the positive and negative voltage goes uneven and the virtual ground starts to swing around which can causes problems when battery voltage is dropping. I suggest to use a "virtual ground generator" like TLE 2426. You can find more information about different power sources to Cmoy from here
annex6666 years ago
I'm not sure shorting the power supply counts as reverse polarity protection - I would suggest a series protection diode instead (preferably schottky as you don't have much voltage to waste). ;-) I'm planning to knock up a headphone amp myself if I get time. I'm perfectly happy with the output from my Zen, but I want to implement some LF crossfeed to simulate head diffraction.
yourtvlies6 years ago
This is really cool! I dig the compact design. I've attempted a CMoy build before with mixed results. I've got a pair of Grado SR-80s that I'd love to drive with an amp, maybe I'll give it another go.
cool, but im to we todd dead to make one of these :-( lol
thadrien6 years ago
Very good!
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