How to Build the CMoy Pocket Amplifier (2009) | Hacker News Reader

How to Build the CMoy Pocket Amplifier (2009)

tangentsoft.net

25 pointsmindcrime21 comments

Seeing stuff like this makes me realize just how far I've come.

A pocket amplifier was one of the first electronics project I undertook, about 10 years ago. It was "hard", in the sense that I didn't know what I was doing, I didn't have the necessary dexterity to follow the instructions correctly, and worst of all, I didn't know enough to know how to evaluate what I was doing wrong.

About a week ago, I finished up a design of a kit, including firmware, custom control hardware, and other goodies, for an FM/Weather Band radio that includes multiple output options, but maintains a very cheap BOM. In short, I've gone from unable to follow instructions to able to synthesize new work based on vague requirements.

I still have problems like this in some of my hobbies, but now I know a little more about myself and I know that "hard" problems often fall into those three categories: knowledge, skill, evaluation.

And once I realized that is how things work, I realized that was what learning programming was like for me, 20 years ago. It has helped me become a more effective tutor.

Turns out, a pocket amp isn't the best "beginner's" electronics project. If I had to teach someone electronics now, it'd start with "all the ways you can release the blue genie from an LED, why it happens, and what you can do about it."

> "all the ways you can release the blue genie from an LED, why it happens, and what you can do about it."

???

https://en.wikipedia.org/wiki/Magic_smoke

"Magic blue smoke" is a euphemism for when you blow/burn electronic components (usually inadvertently, but not always).

The proper design of a simple LED circuit touches on a few fundamentals of circuit design.

It seems the blue genie is an alternative notion of the magic smoke: At the electronics factory, they put magic smoke into the IC, if you let it out, you won't be able to put it back in yourself. (Often there's a puff of smoke when you destroy an IC, maybe when you put the power input onto the wrong lines, or 12v for a 5v chip, etc)

Man, I tried building one of these when I was in high school and didn't know a damn thing about electronics. No multimeter, no oscilloscope, just a soldering iron and teenage idiocy. I put it together and (big shocker here) it didn't work, and I didn't have the vaguest idea of why it didn't, or how to figure out why it didn't. It pissed me off so much that I threw everything away and forgot about it.

I should really consider taking a second stab at it now that I have an engineering degree and a snowball's chance of making it work.

Ah, the good old CMoy. Built one of these in 2005 right as I started college. Didn't know a damn thing about soldering and circuits, just kind of followed along. Building it was my point of entry into hardware and eventually embedded systems. It worked (after several hours of debugging) and got the most interesting looks from my friends.

That was back when I would go to HeadFi everyday and follow the latest news on headphones and amps. Think I even went to a meetup and met Ray Samuels.

Although more complicated and expensive, another interesting amplifier project is the open source O2 amp:

http://nwavguy.blogspot.com/2011/07/o2-headphone-amp.html

To me it seems pretty obnoxious that this O2 design has licensing terms. Most people just freely distribute their schematics and board layouts without a license. I would say that in the DIY community this "open source" amplifier would be considered more restrictive than nearly all others.

In the audio community it is actually very common for shared source designs to be patented and/or distributed under non-commercial restrictions. I think this is because many of the best (known) designers actually build, design and maintain the devices professionally. This might be unlike general electronics/software engineers that do not usually make money off their oss ventures.

To me it's pretty obnoxious that most designs don't have licensing terms; that means that in many jurisdictions it would be illegal for me to print a PCB based off of it.

With this license, anyone cam make and (if they wish to) sell an O2, so long as they don't modify the design, and credit the author. That seems reasonable to me.

Considering how long it took me to get a friggin' Covox Speech Thing (aka. Sound Source) "clone" working (aaages ago), I think I'll pass. Great workout for your soldering skills, though.

Can you get Tripath amps this size these days?

Perhaps not that brand,but there are lots of little switch mode Audio power amp boards out there.

Powering a relatively low impedance device like headphones at relatively high powers with an unbuffered op-amp causes distortion. The CMoy is a classic example of "bad" electronics design.

I remember seeing this one (Op amp configured with some discrete components) back in the 1970s -- also you can change it up a little and use it to amplify very different things.

It's a really cool device and it sounds amazing, the only problem is that you can't really bring it with you often, especially around airplanes :(

Cool design, How hard would it be to modify the design so the amp could be powered by 5V over USB

Not terribly difficult - IDK the opamp specs off the top of my head but you would have to find one that was happy working at single polarity off of a 5V rail. However, it's worth noting that decreasing the voltage kind of defeats the purpose of this circuit, which is to increase the dynamic range of the music you're listening to.

I toyed with that idea, but ended up just buying a 9v wall adapter with a barrel connector, and then wiring in a mate of that connector into the cmoy in place of the battery. Works like a charm, since I only use the cmoy at my desk (it has Fiio D03k optical dac feeding into it).

Hah I actually had built one of these. So cool to see it up again in HN : )

This made me remember that I haven't visited HeadFi in a while.

Reply on news.ycombinator.com