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CMoy Pocket Amplifier


A few days ago I asked how this mystery item could improve the sound of your mp3 players and headphones.  I will now reveal the mystery.

What is it?

This item is called the CMoy Pocket Amplifier and was designed by Chu Moy on the Headwize Forums.  The name Chu Moy has been shortened to CMoy.  The design is intended for do-it-yourselfers and has been wildly successful.  You can see articles all over the internet on design modifications and improvements.  Especially impressive is the wealth of posts on high end headphone sites like  Many members of that site are audiophiles and own pairs of headphones that cost $100 at a minimum and exceed $500 in many cases.  These people take their audio seriously. 

Do you really need an amp?


But why use a headphone amp and why the CMoy?  There are basically two reasons.  Portable music players limit the output of headphone circuits to conserve battery power, so they may not be able to drive headphones cleanly at loud levels.  Secondly, amps built into portable music players are often designed as an afterthought and are often made with inexpensive components that create distortion at moderate volumes. 

Portable headphone amps generally start at about $150 and go up – way up – from there.  It’s not unusual to see one of these amps sell for over $700.  The CMoy provides much of the benefits of these high end amps but for significantly less dough.  You can build one yourself for $20 or buy one for about $35, which is what I did.

What I tested it with


I use Shure E2c headphones, which are considered to be entry level high-end headphones.  In order to extract the best sound from my iPod Classic, I have to crank the volume up nearly all the way.  I also have a direct connect setup in my car that allows me to play iPod music on it.  I upgraded the speakers and love the sound, but the factory stereo system doesn’t have the power to drive those speakers.  So there again I find myself maxing out the volume on the iPod and the car stereo but am not completely satisfied by what I hear.

Where to buy the CMoy Amp


After doing some research, I found a very reputable dealer / manufacturer of CMoy amps on eBay, called Juice2214, who is known for his high quality construction.  He shipped it quickly and I was surprised at its sturdy design and solid heft.  It is not heavy, but feels solid, even though it’s made from a mint tin.  The volume knob feels like the one on my home stereo – very well made.  There is an on / off toggle switch that feels solid, and a blue light that lets you know the unit is on.  It has an input to accept your source, and an output to your headphones, or in my case, headphones or car.   Both input and output are your typical 3.5 mm sockets.

Results of Testing


Before getting the CMoy amp, I was happy with the sound from my iPod, though I had to really crank it to get a decent sound.  But the CMoy has changed my view.  I can now set the volume of my iPod at about 60%, then set the volume knob of the CMoy at about 60%, and I get not only louder volume, but better quality music.  The amp provides the power to drive the miniature armatures in the headphones, making the music more three dimensional.  The CMoy improves the base response, making it more palpable without being overly intrusive.  The highs stand out more and are crisper.  The mids, such as the voice, now seem to stand apart from the background.  Even at moderate volumes the various instruments pop out more than before.  I now realize that without the amp the music sounds flatter.  The amp doesn’t just add volume, it pushes the music through to the headphones.  I have a more pleasurable listening experience at lower volumes.


It is powered by a 9 volt battery that is easy to replace.  The seller emailed me which of the 3.5mm jacks is which, but they are not labeled on the finished product.  I put my own tiny labels on.  It measures about 4.5″ long including the volume knob, by 2.5″ wide, and 7/8″ high. 

Does the CMoy work with a car stereo?

I wondered if the CMoy could add enough power to my car stereo to make a difference?  I performed the same test and was happily surprised to see that indeed, the CMoy added plenty more power to my car stereo.  My car speakers now have more “thump” when used with the CMoy.


I’ve looked at many different mods to improve the sound in both my headphones and car stereo.  I didn’t want to change my car stereo because it works with the steering wheel radio controls and I didn’t want to lose that functionality.  I also felt that my headphones were good enough quality, and using better ones would probably require even more power to drive them.  So the CMoy has turned out to be a very inexpensive, yet efficient way to improve both systems.  I highly recommend it.



Small and light

Inexpensive yet very efficient

Quality build

Powered by a 9 volt battery

Low carbs – great flavor


One extra thing to carry (unless you love carrying your gadgets with you!)

Input / output not labeled

Buy it here for $34.99 plus shipping.

How to Build the CMoy Pocket Amp


February 24, 2008 - Posted by | Accessories, Reviews

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