CMOY shootout!

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Every cmoy uses essentially the same circuit - essentially a textbook implementation of a non-inverting opamp. Only trick is to pick a suitable opamp for the job - Notes on Audio Op-Amps is a good place to start, if a bit out of date. I wouldn't buy a kit off ebay based on the chip it contains - it'll likely be rubbish or fake.

OPA2132 gets a bad rap around here, but it really is a very good opamp, and very easy to use. OPA2227 is a slight upgrade. You'd also do well to consider AD8620. All these chips are dual opamps which will run happily from 9V and supply decent output current - perfect for a cmoy.

If you're after something a little bit fancier than the typical cmoy, AMB Lab's Mini3 or Tangent's Pimeta V2 are excellent choices.
 
I've very recently bought one of these kits, had great fun building it, and have enjoyed listening to it as well! I haven't compared it to my proper headphone amp, but for making my portable CD player (and various MP3 players) usable with decent Sennheiser (HD565) and Grado (325i) headphones, it works!

MyAmp_100_2751.jpg

MyAmp_100_2754.jpg
 
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Cool! Count me in as well. I have the cMoyBB PCB and the TLE2426. Still waiting on some parts (Alps pot, caps, .25W resistors). I have an OPA2134 and an AD8066 for it to start with. Soldering the AD8066 was a challenge!

I'm going for a red coloured theme: red PCB, red LED, red mint tin.
 

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I was interested in the cMoyBB board, but wouldn't want the BB bit!

The BB (bass boost) is switchable or can be eliminated entirely if you wish so. If you want a little less bass boost you can install two lower value resistors or opt for a bass boost potmeter. Try the simulator (Java!) at: JDS Labs - cMoyBB Calculator
 
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Progress! Today some parts arrived, cMoyBB is now nearly finished. I'm still waiting for the Alps pot. A quick test showed that the rail splitter works. I tried a 33K and a 24K LED resistor but settled on the (default) 24K one.

Bass boost resistors are 16K for a lower gain. Bass boost caps are 0.1µF instead of the default 0.068µF. It decreases the bass boost bandwidth a bit.

Had a bit of a problem with one hole on the PCB: it was to small to accept a resistor lead. I successfully used a sewing pin as a reamer.

Lesson learned: such a small PCB requires a finer tip on my soldering iron.
 

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Howdy Mike!

I had the same idea last week so I purchased on of these New Portable Hi-Fi Stereo CMOY Headphone Amp Amplifier* on eBay (end time 17-Feb-10 22:05:34 GMT) Hasn't arrived yet but for only £12ish delivered, it's worth a shot.

This kit use dangerous schematic!

Virtual ground here is simple split of two batterys. It is good, until one battery discharge little faster than other, or you connect slightly used batterys with different voltages. In this case you can get few Volt DC offset, and even burn phones.

To fix it, just add to schematic standard CMoy virtual ground with two resistors or TLE2426, and disconnect battery split from ground.
 
This kit use dangerous schematic!

Virtual ground here is simple split of two batterys. It is good, until one battery discharge little faster than other, or you connect slightly used batterys with different voltages. In this case you can get few Volt DC offset, and even burn phones.

To fix it, just add to schematic standard CMoy virtual ground with two resistors or TLE2426, and disconnect battery split from ground.

I've very recently bought one of these kits, had great fun building it, and have enjoyed listening to it as well! I haven't compared it to my proper headphone amp, but for making my portable CD player (and various MP3 players) usable with decent Sennheiser (HD565) and Grado (325i) headphones, it works!

MyAmp_100_2751.jpg

MyAmp_100_2754.jpg

As I've written above, I have recently completed this kit, and am using cheap NiMH batteries (see the photo above!), which could well discharge at different rates. Is this circuit really likely to damage my precious headphones, and how do I prevent it? (Zigis statement is OK for all you DIY experts out there, but means nothing to me: can anyone explain simply exactly what I need to do?)
 
OK. Your two 9V batteries are connected in series, via some point on the PCB where a lead from each battery is connected by a track on the PCB.

You should disconnect the leads from this point. Now reconnect them (off the board, just to each other).

Now take two 4700 ohm (4k7) resistors. Solder one end of each into the holes vacated by the two leads you removed earlier. The other end of each needs to go to the other connection from each battery (that is, the leads from the batteries that are still connected to the board).

Is that clearer?

EDIT: Looking at the diagram you've posted, it appears that the common point to which I referred may actually be on some kind of terminal block, not on the PCB itself.
 
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OK, here's another way of explaining it, taking into account the diagram.

Going to the terminal block, you have two wires from the battery, and two wires leading to the board. Remove the two wires that lead to the board.

Now, on the board itself, you have two blue capacitors. In parallel with each capacitor, solder a 4700 ohm resistor. That is, solder one leg of resistor to one of the capacitors, then the other leg of the resistor to the other leg of the same capacitor. Now do the same thing, but with the other capacitor.

EDIT: now that I look again, I see that it's not a terminal block, but the power switch. This is a fairly stupid way of switching power.

OK, so if you do what I say above, it won't work, thanks to the power switch thing. What you'll need to do is move one of the wires that remains on the switch, so that instead of being in the same column as the other (looking at the diagram for reference), it's next to the other, but in the same row. That will restore function to the power switch, although it's still a bit dumb. It should now work.

If you have more questions, feel free to ask - perhaps some-one more patient than myself will go to the trouble of modifying the diagram to show you the right way.
 
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