I bought one of these this summer when I was too lazy to build one myself.

It has the optional DC jack and Alps RK097 volume control, bringing the total original price to $60 after shipping. I've since built several of my own for fun and could use some cash.

I'll let it go for $25. It's in the silver rectangular case and "customized" for Sennheiser HD-280 Pro's (64 ohms). It also works well with other headphones I've tried (Sennheiser 32 ohm).

These amps are very effective. The one I'm selling boosts my iPod's signal to 0dB in my car with the iPod at about 3/4 volume (2-channel auxiliary input). My iPod alone is roughly half as loud at MAX volume.

About how much does it take to build one of these?

Ignoring the many hours of free time I spent over the course of one week researching the circuit, it then took me about two hours to get my first design right on a breadboard (dumb mistakes). I can now assemble a custom circuit (variable gains, RCA outputs, bass-enhancing caps, voltage regulators...more) in under 5 minutes.

Putting the circuit on a protoboard (PCB minus the P) and into an enclosure takes a LONG time, at least for me. I have mediocre soldering skills and went through three protoboards before getting one right (as in, not short circuiting traces). I'm talking 4-5 hours per board. You can waste an entire day on it.

Let me put it this way, I've been soldering for years and I spent $50-$60 in parts before I got a single amp working properly in a case. If you're up for the task, go for it. But unless you're skilled with a soldering iron already, you'll most likely wind up paying much more than $30 for your very first build.

From the most common resource on building cMoy amps:

Does DIY save money?

You shouldn't build this amp to save money, unless you are confident enough in your skills that you think you'll get it right the first time and you don't buy extra components for tweaking it. If you mess up your first amp or decide you want to improve the amp after building it, you can surpass the cost of an equivalent commercial amp fairly quickly. This is especially true if you build one of the more complex variants, which can easily require $50 worth of parts; my most expensive CMoy variant has about a hundred bucks worth of parts in it, and one guy I know built an überCMoy costing $300.

The primary purpose of DIY is control, creativity, and craft. It's also a great way to teach yourself electronics: many of the gurus on the forums started out completely clueless, and built a CMoy amp as their introduction to electronics.

The biggest mistake people make when considering cost is trying to make their first amp their last. I don't believe it's possible to make the perfect amp your first time. I think it's a far better plan to build something simple, like the CMoy, as your first project. This will teach you what you need to know to choose your next project.

--Source

Im interested in headphone amps but im still unclear on exactly what they do. Do they improve the sound quality at all or just boost the signal to make it louder? Basically, is it like a sonic maximizer or is it just turning the volume up?

Try ch. 6 in the Circuits book. Basically, opamps take a signal and increase the amplitude of the wave. Different designs can alter frequency ranges. I use larger box caps on my own amps and have noted better bass response in my car. I've found schematics for complicated EQ's based on multiple opamp chips. So, the output of a headphone amp depends on its design. The one I'm selling was made to boost the signal, plain and simple. But as I've learned here, opamps are one of those things where "no ideal opamp exists." Different chips have different acoustical signatures.

An iPod or similar MP3 player will have no trouble driving average low power earbuds and cans. High-end headphones, expensive Sennheiser or Grado models, for instance, have much larger voice coils than basic earbuds. Consequently, the same power supplied to an average set of earbuds is not well matched to such large audiophile level headphones--they need more power.

I can turn my iPod all the way up with my Sennheiser HD-280 Pros and they're still quieter than the stock Apple earbuds at about half volume. It's ridiculous. The opamp increases the amplitude of the music to a more appropriate level--painful levels, if I wish.


I actually use earbuds with my iPod, though. I was interested in matching the output of my iPod with the input impedance of my car stereo.


Drop by and hear it for yourself if you want: 203 Mac.

I might do that actually. I have a pair of 280Pros also, plus i live in kelly so i might as well check it out.

I'll be up until at least [edit: 3am]. Bring over your MP3 player or whatever you want to try it out with. My car is parked close to the quad if you want to hear the difference in that as well...it really exemplifies the power of the amp.

Reply or IM if you need the front door to be unlocked. I know my key works in Kelly, but don't know if the opposite is true.

I'm thinking about designing a PCB for this. Looking at the schematic for it, there is nothing to it. I do not understand peoples foolish notions that PCB's make the audio sound crappy. Yes there have been some crappy designs that were built on PCB's but it was because of poor design. I do not think protoboard routing is any better than PCB, especially when you can put a ground plane on the board and eliminate the ground issue altogether.

Another thing: 9V batteries are notoriously crappy as far as mAH rating. I think it's around 500 mAH. If two AA batteries were used and DC-DC converter used (like the maxim or linear chips), you could get a lot longer play time on smaller and lighter batteries (and cheaper for that matter).

Would anybody be interested if I made a couple PCB's and sold them for $cheap?

I might be interested, but the whole point to most of this hobby is design tweaking, and a single PCB layout will not accommodate most customization. Take a look at this: http://www.headphoneamp.co.kr/ftp/sijosae/Gallery/

I had the same thought as far as batteries go when altering my design. But it's a helluva lot easier to connect a 9V battery than it is to connect 2xAA's. That's why 9V's are used. Battery time is already great. One generic $0.84 9V battery lasted in my car all summer with this amp. Granted, I didn't drive much. Some designs will run for 20 hours on one battery, some 100...battery capacity isn't much of a problem.