what next, help please

right i have built a few cmoy's now and am rather happy with there sound, i have been told there are better headphone amps out there but i do not have a clue what to pick next, could someone please provide me with a schematic or a pcb layout, i was going to attempt to etch my own board for my next project so if anyone has a layout i should try please let me know
It's not easy to suggest something for a "solution looking for a problem" type situation.

However, let me just briefly recap the drawbacks of the basic Cmoy:
* Usually has moderately high output impedance (47 ohms typ.) --> Not a good match for loads with significant impedance variation.
* Limited load driving abilities --> best used with mid/high impedance cans.
* Use on single 9V battery requires rail splitter, hampering performance (current / channel separation).
* OK if unspectacular noise levels (depending on gain)

The next step after a Cmoy would probably be something along the lines of an Apheared-47. (Ask Google for the schematic.) When using NJM4556 type opamps, the typical 47 ohm combining resistors could be reduced significantly (low ohms range), for more power into low-impedance loads.
I'd recommend a split power supply, i.e. two 9 V blocks for +/- 9 V, as already seen on Cmoys. Generous buffer capacitance is recommended, as 9V blocks are notoriously wimpy (I'd use 470µF or even 1000µF / 16+V each).

This setup would pretty much fix the first three drawbacks, and somewhat improve the fourth (due to lower-value gain setting resistors, which actually contribute more noise than the opamp itself in the original Cmoy design, and lower gain).

Using two NJM4556s per stereo amp would make it a bit of a battery hog though, as idle current draw would just about quadruple when compared to the basic Cmoy. A classic two-stage design with a lower-power, low-noise gain amp and a more powerful unity gain buffer may be more economic. (For example, the O2 uses an NJM2068 in the gain stage and an NJM4556 - or actually two - as a buffer, which makes a cheap and cheerful combo. You may or may not want to use the O2's volume control setup, which minimizes noise but makes the amp more prone to input-side overload.)

Actually a fairly big improvement on all fronts could already be had by building a split-supply Cmoy using a '4556, with gain setting resistor values cut by a factor of 10 (e.g. 1k/4k7), a 10k pot, and output series resistors in the low ohms at best (that chip isn't too picky). Much higher output current, somewhat less noise, at twice the idle power of the basic Cmoy.

Compared to this:
* The Apheared-47 achieves twice the output current and reduced distortion, at twice the idle current.
* The basic two-stage amp achieves reduced distortion and up to 10 dB less noise, at 1.6 times the idle current.
* An O2-alike achieves twice the output current, significantly reduced distortion and up to 10 dB less noise, at 2.6 times the idle current.


2010-11-26 7:33 pm
This is not to hack the Original post but,
I see sgrossklass talking about low impedance loads.

How low impedance can the Apheared-47 drive?

I am myself concerned with building an amplifier for my RE272s with 20Ohms impedance. Realizing that this rated 20Ohms varies with frequency, i suppose that this 20Ohm phone can have a dip of 10Ohms at some frequency too. I want to have enough current to drive this 10Ohms.

Is it possible to build such an amp?

right first off dont think i am ready for smd yet, but i will keep it in mind for when i am, and thanks sg i will look up that up and see if its within in my skill range, and my cmoy i built has 1000uf 16v nichicon ka's and 1uf mundorf mkp output caps and has a opa2107pa op amp, and it has a good sound for what it is, and i am gonna look up more into what you have said


2003-09-03 12:17 pm
Grado are nice headphones to start with :)

I've got a weakness for this project: The Cavalli-Kan Kumisa III Stereo Headphone Amplifier PCB are available, making it quite difficult to mess up. Plenty of documentation too. And it could be the last amp you build.

The one at the top of this page is fun too but it's a bit more complicated as no layout is available. Good DIY headphone amp?

And you have this which is quite trendy now: O2 Headphone Amplifier Full Kit Seems like a nicely put together kit for the price. Makes things easy too.
at $2.90 each it aint bad when it needs 4, i aint worried about that its the postage thats killing me they want $26 just to post the board, i mean for that price i would want it flown by an eagle to my front door, so i might get the pot and the jfets npn and pnp's with the board thats all in all £45ish and the alps pot is £19 here alone so will sit down and price the board up later and see if its gonna save me an extra bit of cash, another thing thats got me is its using all std caps all non audio so might swap them out for an extra few pence, get paid friday next week so i can um and ar over this for a week