CMoy

A CMoy is a pocket headphone amplifier originally designed by Pow Chu Moy [1][2]

Common CMoy in Altoids tin
CMoy in parts

The headphone amplifier is designed around single or dual-channel operational amplifiers (op-amps) such as Burr-Brown's OPA2134 or OPA2132PA, however, a wide variety of op-amps have been successfully implemented. As the op-amp directly drives headphones some care should be given when choosing an op-amp, some op-amps are not suitable for such low impedance loads and will result in poor performance.[3][4][5] (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.[6]

Circuit

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.

References
  1. Hertsens, Tyll (March 15, 2016), A Memorial to the Grandfather of Headphone Enthusiasm
  2. headwize.com Headphone Resource Site and public discussion Forums.
  3. Northwest Audio & Video Guy (August 10, 2011), Op Amps: Myths & Facts
  4. Großklaß, Stephan (2014-07-15), A Classic Hi-Fi Misconception
  5. Young, Warren (October 31, 2016), "Notes on Audio Op-Amps", Audiologica
  6. Rutter, Daniel (20 March 2004). "Review: Chu Moy headphone amplifier". Dans Data. Retrieved 2009-06-03.
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