Sunday, 11 November 2007


CMoy is very simple portable headphone amplifier. The amplifier was originally posted by Chu Moy on The best source of information about this amplifier is article How to Build the CMoy Pocket Amplifier. If you use Google, you will find many pages and pictures about CMoy. Few months ago I decided built this amplifier also. In my post you can find my experience with creating this simple but very good amplifier.

First of all I prepared the schematic. It is standard CMoy schematic, non-inverting amplifier with gain 11. The power supply is making virtual ground (half of supply voltage). My power supply unit has two possibility. Firts possibility is use passive voltage divider, consist of two resistors R1a and R1b. In this case it is necessary use also two electrolytic capacitors C1a and C1b. The second possibility is used active divider TLE2426 from TI. In this case it is necessary connect only one capacitor between Vcc+ and Vcc-.

1. Schematic

After I had schematic I designed the PCB. My PCB is prepared for both variants of power supply. I can connect also one or two 9V batteries. In first case it is necessary shortcut one supply connector P1a or P1b. Power switch can be connected to P2.

2. Design of PCB

I let make the film in Prague's design studio Winter.

3. Film

The PCBs were made in Prague's company PLspoj.

4. PCB

I assembled CMoy during one hour. Instead of R5 and R25 is used only wires. These resistors are assembled only in case of oscillation. The value should be few ohms. Now I have to find some good box, and put my CMoy inside. It will be maybe most difficult part of building CMoy amplifier :-).

5. Finished CMoy

The sound is very good for so easy and small device. It can improve the sound of MP3 players, mobile phones and other portable devices. I would like to make some measurement of frequency characteristics, THD and also try to use different OpAmps, but unfortunately I don't have enough time to make it now.

A lot of information about CMoy :

Step by step tutorial how to make CMoy:


TTrev said...

Very Nice Cmoy you have there! Great job! I do have a blog which also showcasting my cmoy... Can we do a link exchange? My cmoy can be found at

donaxav said...

Hi, good job you did, congratulations !
It's clear and neat, specially for the USB card.

Would you like to sell a couple of CMoy cards ? I'm living in France.



Miroslav Batěk said...

Hi Xav,
If you are interested in CMoy PCB, I can send you a couple of CMoy. Please write me to my email We can discuss details.

Icaro said...

what about powering it with a USB connected to a PC?

Patrick said...

Probably best headphones in Australia.