# CMoy

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> Source: https://en.wikipedia.org/wiki/CMoy
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{{Self-published|date=September 2020}}

[[File:Cmoy there.jpg|thumb|Common CMoy in [Altoids](/source/Altoids) tin]]
thumbnail|right|CMoy in parts
A '''CMoy''' is a pocket [headphone amplifier](/source/headphone_amplifier) originally designed by Pow Chu Moy.<ref>{{citation |first=Tyll |last=Hertsens |date=March 15, 2016 |url=https://www.innerfidelity.com/content/memorial-grandfather-headphone-enthusiasm |title=A Memorial to the Grandfather of Headphone Enthusiasm |url-status=dead |access-date=March 5, 2018 |archive-date=March 5, 2018 |archive-url=https://web.archive.org/web/20180305202558/https://www.innerfidelity.com/content/memorial-grandfather-headphone-enthusiasm }}<!-- "...on February 12, 2016, with no notice or fanfare on the web, Pow Chu Moy, founder of HeadWize (the first headphone forum) and creator of the Chu Moy Headphone Amplifier, passed away in Reno, Nevada...--></ref><ref>{{cite web |archive-url=https://web.archive.org/web/20150415003947/http://headwize.com/?page_id=707 |url=http://headwize.com/?page_id=707 |archive-date=2015-04-15 |website=headwize.com |title=A Pocket Headphone Amplifier |first1=Chu|last1=Moy}}</ref>

The headphone amplifier is designed around single or dual-channel [operational amplifiers](/source/operational_amplifiers) (op-amps) such as [Burr-Brown](/source/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.<ref>{{citation |author=Northwest Audio & Video Guy |date=August 10, 2011 |url=https://nwavguy.blogspot.com/2011/08/op-amps-myths-facts.html |title=Op Amps: Myths & Facts}}<!-- "Some op amps have been judged in the wrong applications. The Cmoy headphone amp is just such an example..."--> </ref><ref>{{citation |url=http://stephan.win31.de/music.htm#hifimiscon |title=A Classic Hi-Fi Misconception |first=Stephan |last=Großklaß |date=2014-07-15}} <!-- "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 is 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." --> </ref><ref>{{citation |url=https://tangentsoft.net/audio/opamps.html |title=Notes on Audio Op-Amps |date= October 31, 2016 |first=Warren |last=Young |website=Audiologica }} <!-- "This article documents my testing process, and the results for many quality op-amps, plus some jellybeans" --></ref> (See [Op-amp swapping](/source/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](/source/protoboard), has a lower parts cost than other headphone amplifiers, and can run for many hours on a single 9&nbsp;volt battery.<ref>{{cite web |url=http://www.dansdata.com/cmoy.htm |title=Review: Chu Moy headphone amplifier | date=20 March 2004 |first=Daniel |last= Rutter  |website=Dans Data |accessdate=2009-06-03}}</ref>

==Circuit==
A typical CMoy consists of two identical [AC coupled](/source/Capacitive_coupling), [non-inverting operational amplifier](/source/Operational_amplifier_applications) circuits each with a 100k[Ω](/source/Ohm) 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](/source/virtual_ground). Many virtual ground circuit options are presented in the various CMoy tutorials found online.

== References ==
{{reflist}}

==External links==
*[https://tangentsoft.net/audio/cmoy-tutorial/ How to Build the CMoy Pocket Amplifier] 
*[https://github.com/Wanderingidea/Joechei Joechei – Yet Another Cmoy Headphone Amplifier]

Category:Audio amplifiers

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Adapted from the Wikipedia article [CMoy](https://en.wikipedia.org/wiki/CMoy) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/CMoy?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.