Issue #16 February 2006

The sound of sharing: Headphone amplifiers built the open source way

The Super Mini Moy, based on the CMOY design.

Headphone amplifiers. Open source.

If you don't know the connection between the two, you may be among the hardcore audiophiles who've dropped sick amounts of money to get better-sounding music into their headphones.

Basically a headphone amplifier provides a link between your music player, your headphones, and you getting your groove on.

Your first thought: But I don't really need my music to be louder. No, you probably don't. And we don't recommend it. Especially if you're listening to something like Nickelback or the latest Lindsay Lohan vanity album.

But this isn't just about volume; it's about quality. Sharp, crisp highs. Clear, undistorted lows. Instruments, voices, the smallest details—all are more pronounced, with greater depth. Especially if you have a pair of large headphones like those made by Sennheiser and Grado that can handle a wider range of frequencies and need extra power. Power that many portable devices and computer sound cards just don't devote to the audio output. It's no surprise why—I don't care how much you love great sound, if your device doesn't have enough battery power to make it through a morning commute, sound isn't going to mean squat. But really, no matter what headphones you use, the right amplifier can make them sound better.

Not long ago if you wanted to buy a headphone amplifier, you needed money—and lots of it. Today you can not only find inexpensive battery-powered headphone amplifiers, but you can build one yourself.

One person you can thank for this is Chu Moy. If you see the phrase "CMOY" used to describe an portable amplifier design, that's his. He designed a very simple headphone amplifier that could be built with inexpensive parts by anyone so inclined, with do-it-yourself electronics skills and an afternoon to spare.

And the best part: he posted step-by-step instructions to show how he did it.

His design inspired hundreds of imitators and improvements, and even individuals making a business out of selling amplifiers to people like me who shouldn't go near a soldering gun. Just look for headphone amplifiers on eBay. You'll find countless variations. You can even pick a candy tin you want your amplifier custom-made from.

"There's no secret as to what goes into them. Some other builders go as far as scraping numbers off of the chips."
Drew Dunn, Shellbrook Audio Lab

I first learned about headphone amplifiers like these when a friend bought one and was sent two by accident. He let me listen--I sent money and kept the amplifier. (I know what you're thinking, and yes, sending two is great marketing strategy.)

The amplifier I bought was made by Shellbrook Audio Lab, a web business Drew Dunn originally built around replicating the Moy design with his own improvements. Today he sells four amplifiers as well as a range of audio cables.

Dunn, an electrical engineer in his day job, first got interested in headphone amplifiers when he bought a Neuros MP3 player and tried to use it with his Grado headphones. "It didn't quite have the juice to drive those Grados very well," he says.

That's when Dunn ran across the website for Chu Moy's amplifier.

"I'd built plenty of home audio equipment, but I'd never even thought of a headphone amplifier. I built it, and it worked pretty well. So I built some for friends. Somebody I work with said you ought to sell those things. So I started selling them on eBay, and things just snowballed from there."

The first CMOY amp he built took a couple of hours, and he used the tutorial on as a guide.

"Everyone who starts building headphone amps starts with that amplifier," he says. "The design is pretty straightforward, so the first thing people often do is look for ways to make it better."

He's been able to offer advice for other people wanting to make improvements. Such as adding a battery charger or buffers to drive low-impedance headphones that aren't as sensitive.

What makes Dunn's amp different from the original amp designs published on the web is that the DIY versions have to be designed for anybody to build. "The amplifiers that I design, obviously they have to be buildable, but they only have to be buildable by me," he says. "I don't have to make any special considerations for anyone else's ability. It's all a matter of designing the amplifier to perform as well as it can."

His focus is finding the best parts available to him, then making sure all of those parts have a synergy and work well together. For example, making sure the power requirements are met.

"There's no secret as to what goes into them." he says. "Some other builders go as far as scraping numbers off of the chips."

Builder becomes contributor

Drew has also used this experience to become a contributor, working on amplifier design originally created by Pete Millet. Someone came across the Millet design and started asking questions on the web about what could be done with it. Since Dunn had design software, he offered to do the design work based on everyone's input.

"He [Millet] was pretty excited about the fact that people were interested enough in the design to try and make some improvements to it, so he got behind it as well," Dunn says.

With their original group design, they pooled their money and bought 500 circuit boards at a discount, and then Drew worked on the manufacture of the boards, selling them back to the group at cost. As he runs out of boards, they update the design. They're currently on their third iteration of the board. It's also led to spin-off projects for others.

"It's exciting. A lot of people have learned a lot of stuff. I know I have. That's really the first time that I've worked with tubes in amplifiers in that way. A lot of us are familiar with opamps and doing things with transistors, so this was a totally different way of working." he says. "It was a nice learning experience."

The plans and the board files for the design are available on DIY Forums.

"There are no restrictions on it at all," he says. In fact, Dunn said Millet was specific in that he didn't want his copyright on the design. "He didn't want it to be copyrighted by him, so it's not copyrighted by anybody," he says. "It's free for anyone to use."

Dunn also sells a modified version of the amplifier, which he calls the Hybrid Head. It's based on the original Millet design, but doesn't include some of the elements of the design that were added to meet individual requests.

"When I decided to sell one through the website, I made it the way that I would have made it if it were just for me," he says. "Like all of the other amplifiers, there's no secret to what parts are in it. There's nothing proprietary or anything special that I won't tell anybody else."

So, it seems like an obvious question, but why do people buy the amplifiers rather than build them themselves? Dunn offers three reasons:

First, the time involved.

Second, the ability. "To me it seems like it's nothing to put these things together because I've been doing this for a long time. But to an awful lot of people it's something they just don't want to undertake because they feel that they may not be able to accomplish it."

And third, money. "You can buy all of the parts, but you need some equipment to go with it. You need to buy a soldering iron, the solder, some tools," he says. "Unless it's something you're doing as a hobby, you can end up spending a pretty fair amount of money for some tools that you're just going to use to build this amplifier."

Still, one of the things Dunn often suggests to people online is that, especially with the CMOY amp, that it is worth trying to build one yourself because it's so cheap. Especially if you've never soldered anything together before.

"If you make a mistake, you haven't burned up a $50 part. The most expensive thing for the amplifier is probably the case, and that's $4 or $5," he says. "And if you make a mistake it's easy to fix because there are a lot of people that are willing to help."

I learn, by coincidence, that Dunn also happens to be a Linux user at home and work. (Fedora™ and Red Hat® Enterprise Linux® even.) So naturally I have to ask a perfectly leading question about how he sees the design of these amplifiers, and his participation in the Millet amp in particular, as a match to the open source model.

"I think the Millet amp is just as much an expression of the open source philosophy as open source software. Nobody owns it and everybody is welcome to provide input into what it should evolve into," he says.

"Everybody who puts one together or buys one already put together by someone is absolutely amazed at just how well it performs. And I think they're amazed that it's just a bunch of people that got together and said they want to make something cool, and we're going to start out with this project as its basis, put our heads together, and come up with something."

Of course Dunn's business is one of the many that can make an amp for you. A quick Google search of headphone amplifiers or "CMOY" offers many options for high-quality, inexpensive headphone amplifiers. With the masses of people taking more of their music with them by way of Apple iPod, Creative Zen, Dell DJ Ditty—music lovers will no doubt be looking to improve sound quality as the next logical step to getting more love from their music.

The parallels between what people like Moy and Dunn have done with sharing their work and the open source model of developing Linux are so apparent I won't spend a heavy-handed paragraph talking about them. OK, after this one.

But still, when I flip the switch on my amp and see the blue light glow, I can't help but appreciate those who know how to share.

About the author

Jonathan Opp is a Manager of Marketing Communications at Red Hat. He spends his free time reading, taking photos, playing soccer and following British football, and listening to whatever music he can get his hands on.