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This headphone amplifier circuit is different to conventional modern construction techniques in that it is air Wired,P2P (peer to peer) or free form wiring just like in the good old Valve days before the intervention of  PCB's and the transistor.

Rather than a traditional enclosure, the hole circuit is encapsulated in polyester resin to enhance the internals.


If your reading this and thinking why do you need an amplifier for headphones then click here

Although allot of cMoy headphone amplifiers are designed to be portable this one is designed for the desktop although a battery pack could be made also.


This is a pretty long instructable so "make a brew" as we say in Yorkshire and get comfy .

On the upside there is plenty of pictures :)

Step 1: The Schematic

Here is the EaglePCB schematic of headphone amplifier it follows the cMoy design



The component list is as follows

Power supply section

1x DC Power Jack
1x 5mm LED
R1LED      : 1x 1k  to 10k 0.6 watt metal film resistor   (For the Power LED, Anywhere from 1k to 10k will be good it all depends on the input voltage and how bright you like your LED.)
CP1/2        : 2x 470uf 35 or 50v  Power Capacitors 
RP1/2        : 2x 4.7k 0.6 watt metal film resistors   (For the power supply Voltage divider)

Amplifier section

IC1       : 1x  OPA2107 Dual Operational Amplifier
C1L/R  :  2x Wima MKS 0.68uf 63v  Capacitors (for the audio signal input)
C2/3     :  2x 0.1uf Polyester Box capacitors (To stabilise the OP-AMP)
R1LED :  1x 1k      0.6 watt metal film resistor (1/2 Watt)
R2L/R  :  2x 100k  0.6 watt metal film resistors (1/2 Watt)
R3L/R  :  2x 1k       0.6 watt metal film resistors  (1/2 Watt)
R4L/R  :  2x 10k     0.6 watt metal film resistors   (1/2 Watt)
R5L/R  : JUMPERED (optional,)
2x 3.5mm Stereo Jack Sockets


Downloads: EaglePCB .SCH Schematic and PDF below

<p>I am a electron pixie noob. How does this not overheat or melt?</p>
<p>Good Instructable. One kinda has to want it to go to all the trouble, but once over the &quot;I want it&quot; hurdle, it's cool!</p>
??
<p>Any for sale?</p>
<p>same here? :)</p>
<p>this is great project, excelent job!!</p>
<p>Excellent but if it is a failure ???</p>
<p>very nice project</p>
<p>Did you peel the silver caps before use or do they come like that?</p>
<p>A thing of beauty.</p>
<p>This is one of the best instructables I've ever seen</p>
<p>I love this brick of art!</p>
<p>I love the way the components and wiring are made into art in this project - beautiful build :) makes it a look a bit sci-fi!<br><br>I tried to respond to the reverse battery protection comment below but the reply button won't work, so I've put the response here instead<br><br>A better method of reverse battery protection is to use a P-type mosfet &quot;the wrong way round&quot; in series with the positive supply line, and it acts like a kind of &quot;smart diode&quot;. Connect the gate to the negative supply. Then when the battery is the right way, the mosfet's intrinsic diode conducts the first little bit of current, enough for it to turn on, then it acts almost like a short. Connect the battery the wrong way and it<br>stays off, no current can flow.</p>
This is so beautifully crafted! ? look at those curves off that IC! Oh it's orgasmic
<p>The P2P you mention means point-to-point, not peer-to-peer.</p>
<p>One technique for reducing air bubbles is to have your entire assembly on a board. Once you have done your pour, slide the board so that one edge is supported on the edge of a table and tap the underside of the board to dislodge any air bubbles, which will rise to the surface. </p>
<p>Excellent Work!</p>
<p>This is one of my favorite Instructables of all time. I have shared it with many, and am hoping to one day try making it myself.</p>
<p>Glad the readers are still enjoying my Instructable.</p><p>Its great to see the readers builds :)</p>
<p>Its Very Nice !!!!!! </p>
<p>Remake this amp for second time,added two 9V rechargeable battery and edit the schematic after discussion with my dad.Replacing OPA2107 with TL072NC,added a plastic shell casing and a hook(I need portability).Works perfectly with my Alessanddro MS1i.</p>
<p>Hey! how you identify the audio_in 1,2 and 3 pins in socket?</p>
Great instruction ! :D <br>*the diode by the led is just for visual purpose
<p>Hey! how you identify the audio_in 1,2 and 3 pins in socket?</p>
<p>Hey can you please help me with the OPA2107 replacements. i can't find it</p>
<p>Hey, I just wanted to say that this method for prototyping is extremely beautiful. Its very inspiring!</p>
<p>Add a series schottky diode with the positive supply, and that should make any possibility of capacitor failure from reverse polarity very minimal, while not reducing the supply that much from the ideal voltage.</p><p>Keeping the LED after the diode will work as a signal of reversed polarity.</p><p>Also, for a better spread light from the LED to the resin, you could have sanded it lightly so it would get a white finish to it.</p>
<p>Another method used to protect against polarity reversal is to put a diode back-biased across the power input. This way the diode shorts out a reversed power supply. </p><p>The advantage of this method is that it does not introduce any voltage drop. But the diode needs to be hefty to hold the power supply in its current limiting mode without opening.</p>
<p>In series with that back-biased diode, add the coil of a relay. The coil will limit the amount of current passing through the diode. Then, have the relay break the power connection to the rest of the circuit and maybe light-up a red LED to show the fault condition.</p>
<p>I like your idea much better! I don't like the reverse-diode protection because it could potentially damage the power supply, or it could be damaged and impossible to repair (in this particular case). Having the relay there makes a lot of sense, and there's a lot of very small relays in the marked so it wouldn't add much weight or complexity to the project.</p><p>Honestly going to use that in my builds from now on!</p>
<p>I think it might be better, now that I thought about it some more, to either use a SSR instead of a mechanical relay to cut down on the time it takes to shut down power, or to wire a mechanical relay with a blocking diode so it energizes with correct polarity and block power to the amp until the relay has time to trip</p>
<p>hey there, love this instructable, how much did this cost you make and how long did it take ?</p><p>i shopped around for an OPA2107 and some places wanted &pound;12 for a single piece :O..</p><p>but, looks like you put some real time and effort into yours ?</p><p>i wonder what it would look like it it had a frosted with a blue LED in it! :O</p>
Hello,<br>This is an awesome instructables!! And the end product looks awesome<br><br>Just a Q: how would I go about adding a potenciometer?
I have never seen precision and art like soldering like that. You operated like a surgeon! Outstanding!
<p>Dear all. </p><p>I am from Viet Nam.<br>I dont know name of Liquid make resin molding.<br>Where do me can order this liquid? (Amazon, alibaba)<br>Please help me.</p>
<p>Usually you are not supposed to take plastic to a belt sander because it clogs up the sandpaper. Did you have any problem in this regard?</p>
<p>Not if you run it slowly and don't over heat the work.</p><p>Depends very much on the plastics.</p><p>I am willing to sacrifice a &pound;2 belt to get the result.</p>
<p>That's just what I did, sacrificed a belt. </p><p>But in retrospect, after doing my first ever casting, I do realize that if I sanded more slowly this would not have happened. </p><p><a href="http://www.instructables.com/id/Ice-Cube-Clock-3/" rel="nofollow">http://www.instructables.com/id/Ice-Cube-Clock-3/</a></p>
<p>I noticed that you have Top and side views but not bottom. I think a bottom view would be incredibly useful understanding the layout.</p>
<p>http://cdn.instructables.com/F6U/W3U1/H27LRR81/F6UW3U1H27LRR81.MEDIUM.jpg</p>
<p>Beautiful work.</p>
<p>Very sexy!</p>
<p>Nice <br>nod to some of the craftsmanship of valve days reminds me of Hiwatt amp porn <br>like <a href="http://hiwatt.org/images/70HiwattFacesGuts.jpg" rel="nofollow">http://hiwatt.org/images/70HiwattFacesGuts.jpg</a></p><p>Inspired, <br>beautiful build &ndash; much more &ldquo;3D&rdquo; than I&rsquo;m used to looking at electronics.</p><p>Love <br>the screwdriver lead bending tip for this kind of application too. </p>
<p>A step by step instructable where the &quot;why&quot; was explained just as well as the &quot;how&quot;. I'm going to do this project not just to have a headphone amp for my bose over-ear phones, but to learn more about electronics along the way. Thanks! May be the best instructable I've read.</p>
<p>stunning, never wanted a pre amp untill now.</p>
<p>Beautiful preamp!</p>
<p>Excellent job man!!</p>
Amazing and looks cool. I love it great
<p>Wow! pure genius! </p>
<p>I know it's counterintuitive, but actually pouring a thin stream of resin from a height of 3 feet or so is better for eliminating bubbles than pouring close to the mold.</p>

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Bio: Rupert Hirst "If I can't beg,buy,borrow or find something then I guess I will just have to make it!"
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