How to Build the CMoy Pocket Amplifier (2016) | Hacker News Reader

How to Build the CMoy Pocket Amplifier (2016)

tangentsoft.com

41 pointsbrudgers20 comments

I've had one of these someone else on ebay made for like, 10+ years? Still working good and sounds great.

Me too! Mine was in an Altoids case. They warned me not to bring it on a plane.

So do I. There was a guy in Western Australia selling pre-made ones with a choice of different connectors and charging capabilities.

Oh wow that takes me back. I originally got into engineering as a career over a decade ago because of DIY electronics (especially guitar stompboxes) and I remember the CMoy making the rounds then too. Thanks for posting, I'm now starting my day with happy nostalgia vibes.

Same here! A CMoy amp in an Altoids tin was the first useful project I soldered up while in high school years ago. Part of what made it accessible to a high schooler at the time was that you could sample the Burr Brown amps for free. Obviously the intent wasn’t to give freebies to teenagers, but I’ve since returned many, many multiples of that to Texas Instruments in products I’ve been responsible for!

Anyone interested in the topic should check out the original site / forum, HeadWize, now in memorial mode.

https://headwizememorial.wordpress.com/

It saddened me to hear about the circumstances: https://headwizememorial.wordpress.com/pow-chu-moys-memorial...

Anyone wanting to build that circuit should do a quick search, it has been much improved over the years, and there are even off the shelf PCBs that fit right in the case for cheap.

Personally, it is still cool. I think I have three or four of them in the house, and I have built countless CMoy-BB versions for my friends when they were selling the PCBs. It is pretty impressive, I still have one powering my very large Sony headphones right now.

Audio is a very interesting and strange hobby. For example, this amp is probably fantastic, but 90% of people probably don't even need one, and those who do can probably get away an Apple dongle or something similar.

Some people will swear XYZ amp makes their audio sound better, but that's more a function of taste, the DAC, and/or distortion handling mechanisms inside the amp, and that's itself is an incredibly topic which again 90% of users can ignore.

The CMoy can affect the sound, which is a hazard if you're a purist and fun if you're not. It's biggest win is being a fun and accessible (cheap and simple) entry into electronics. A good audio circuit should have low output resistance. Granted you can get that with a CMoy, but the popular/expensive models don't meet that criteria.

https://nwavguy.blogspot.com/2011/08/op-amps-myths-facts.htm...

https://nwavguy.blogspot.com/2011/05/cmoy-ebay-headphone-amp...

[ Deleted incorrect statement ]

???

That would dissipate about 50% of the power in the output circuit, and unless the impedance variance across the frequency ranges matches the headphones, then it will significantly color the sound (as the fraction of power dissipated will vary from the nominal 50%). Power amplifiers almost always want to be orders of magnitude lower impedance than the loads they are driving (so a fraction of an Ohm for driving speakers) for this reason.

Useful if connecting higher end headphones, not useful if you're only going to connect simple low power in ears.

The moment you connect any sort of bigger headphones that do not have their own amplifier to "standard" 3.5mm on most portable devices (even laptops), you find yourself benefitting from such pocket amplifier.

The power available on those outputs tends to be quite low, so attaching higher impedance headphones means the resulting sound is quieter, which results in user cranking volume up to compensate, which makes the usable range of volume smaller for adjustments, but also that often quality noticeably falls down because most amps have more distortion at upper ends of power.

Depending on devices, sometimes you even get noticeable difference in power drain.

My comment stands for over-ear headphones as well - it's just not going to matter for 90% of users. An Apple dongle is usually more than enough.

I have several different amps, a tube pre-amp, several DACs and a Qudelix 5k DAC. I regularly switch between an HD600, HD650, HD560s, HE4xx and Audeze Maxwells. I can maybe count on one hand when I thought one combination sounded "better" than another, although I'm sure I could bump up this number if I tried. The problem is 90% of the time it just doesn't matter.

There's loads of resources on the net that talk about this, e.g.

https://www.youtube.com/watch?v=K8zAko5G6eg

Most of the time the differences are not that important, unless, as the adage goes, you're using the music to listen to your equipment rather than using the equipment to listen to your music. Which... 90% of users don't do.

The difference may be down to "Apple Dongle" in the era of USB-C/Lightning connectors and no 3.5mm - I know that despite not having particularly high impedance headphones, the difference was huge - and I specifically avoided "listening to equipment" and didn't invest too much into it.

One use case that is great is to have two CMoys when using a headphone splitter; you get two independent volume controls. I miss devices (like the original Walkman!) with two headphone jacks...

Yep the Apple USB-C to 3.5mm dongle is insanely good. Apart from looking like a ridiculous flimsy thing compared to chunky desktop amp/dac setups, it obviates a good chunk of the mid-fi market for a fraction of the price

Poorly matched output impedance is one place where headphone amps do have a place. For example when plugging headphones into a speaker amp / AV receiver, where the headphone jack connects to the amp with a resistor in series, the end result can be anywhere from a significant bass boost to just plain bad

Be very careful that for most people, the first impression of "sounds great" is in reality an "is louder", the loudness wars in audio production have led to less and less significants bits of data being needed to carry music, an objective measure of information loss. Also I will not get started on hearing loss, but... if this was somewhere else in your body than your ears, what DIY project would you accept there?

[I am not an audio engineer]

Compression was the preferred munition during the loudness wars, not amplification.

Recordings producing more acoustic energy were made by reducing dynamic range.

You're totally correct, and just to clarify for anyone who's not into audio/DSP this isn't referring to "data compression" but rather dynamic range compression. Basically quieter sounds get amplified so that the difference between a quiet sound and a loud sound is smaller, and then the whole thing gets amplified so that it's dancing right on the edge of clipping.

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