A CMoy is a pocket
headphone amplifier
A headphone amplifier is a low-powered audio amplifier designed particularly to drive headphones worn on or in the ears, instead of loudspeakers in speaker enclosures. Most commonly, headphone amplifiers are found embedded in electronic devices t ...
originally designed by Pow Chu Moy.
The headphone amplifier is designed around single or dual-channel
operational amplifiers
An operational amplifier (often op amp or opamp) is a DC-coupled electronic voltage amplifier with a differential input, a (usually) single-ended output, and an extremely high gain. Its name comes from its original use of performing mathem ...
(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. (See
Op-amp swapping
DIY Audio, do it yourself sound reproduction, audio. Rather than buying a piece of possibly expensive audio equipment, such as a high-end audio amplifier or speaker, the person practicing DIY Audio will make it themselves. Alternatively, a DIYer ...
.)
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.
Circuit
A typical CMoy consists of two identical
AC coupled,
non-inverting operational amplifier circuits each with a 100k
Ω 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
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External links
How to Build the CMoy Pocket AmplifierJoechei – Yet Another Cmoy Headphone Amplifier
Audio amplifiers