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Common CMoy in Altoids tin
CMoy in parts

A CMoy is a pocket headphone amplifier originally designed by Chu Moy on the Headphone Resource Site and public discussion Forums.

The headphone amplifier is designed around single or dual-channel op-amps such as Burr-Brown's OPA2134 or OPA2132PA, however, a wide variety of op-amps have been successfully implemented. The op-amps directly drive headphones, even though most are not designed for such low-impedance loads, leading to poor performance and audible differences between op-amps that would not exist in a good design.[1][2] (See Op-amp swapping.)

The amplifier's design is quite simple. It consists of only a few components, can be assembled on a small section of protoboard, has a lower parts cost than other headphone amplifiers, and can run for many hours on a single 9 volt battery. The CMoy headphone amplifier can be fit into Altoids tins and can often be found for sale on eBay by searching for "CMoy".[3]


A typical CMoy consists of two identical AC coupled, non-inverting operational amplifier circuits each with a 100kΩ input impedance.

Power is supplied to the opamps using a dual power supply, which effectively divides the input voltage source in half to create a virtual ground. Many virtual ground circuit options are presented in the various CMoy tutorials found online.


  1. ^ Op Amps: Myths & Facts- "Some op amps have been judged in the wrong applications. The Cmoy headphone amp is just such an example..."
  2. ^ A Classic Hi-Fi Misconception - "Anyone who decided to build a cMoy headphone amp using a trusty TL072 and single 9V battery to drive his Grados is probably going to be inclined to think that the chip sucks (since it's really lousy when it comes to driving low-impedance loads, which gets even worse on low supplies) – yet the same opamp may be totally inconspicuous when used in a line-level inverter on +/-15 V."
  3. ^ "Review: Chu Moy headphone amplifier". Retrieved 2009-06-03. 

External links[edit]