[oxus]

Hi guys,
 
This is my first post here.. Please be gentle..
 
I just bought this CMOY copy from the seller:
http://cgi.ebay.com/New-Portable-Hi-Fi-Stereo-Amp-CMOY-Headphone-Amplifier-/230516969458?pt=LH_DefaultDomain_0&hash=item35abe1cff2
 
I am wondering if there is anyway I can improve the quality? Maybe changing opamp? Or by improving the circuit a little?
 
I received comments from another ebay seller saying that: "[size=10pt]It uses a very simple circuit which gets its virtual ground from the center tap of two batteries, in theory fine BUT in the real world batteries go down at different rates this will cause an imbalance and a large DC offset, this offset will be amplified and can damage headphones. the better amps on ebay use a rail splitter or a buffered ground to avoid these problems."[/size]
 
[size=10pt]Is this true? Are there anything I can do to improve the circuit or prevent my headphone from being blown up?[/size]
 
 
The second question: I bought this CMOY to try out the effect of an amplifier. I have a 2nd gen iPod Nano and a Sansa Clip. Does the sound improve if I use the LOD on the nano? Or is it similar? I have heard conflicting informations on this.
 
The headphones I have are: JVC S150, JVC FXC50, Sennheiser IE8, and Altec Lansing UHP336.
 
Thank you in advance!

 

[ThermL]

Tangent has a very good write up on his website about VG circuits in cmoy amps. You can check it out here along with a lot of other information on CMoy amplifiers.
http://tangentsoft.com/elec/vgrounds.html

 

[oxus]

That's a good website! I also found it from my google search and tried reading before I posted here, but didn't really understand it. My background is not electronics. Maybe I should spend more time trying to understand these circuits.

 

[ThermL]

Well reading the schematics and creating a simple railsplitter with the Texas Instruments chip would be a good start among all the other tweaks.  For the two CMoys I just ordered parts for i'm going with 470uf caps in the power section to provide a better response and impact from the base. Another simple bit of tweaks you can do is going higher uf caps instead of the .1uf filtering caps. Maybe something around the ranges of 1uf. That should also help improve the bass handling of the amp.
 
AFAIK, the amp should greatly improve the sound coming out of your nano as it is a rather weak source and while I honestly don't know much about your headphones, I can't see how they wouldn't see an improvement.
 
Like you i'm an audio newbie and i'm just starting to get into electronics so Tangent's website has been a huge help. I've practically read everything on it twice and it helps a lot coming to understand the circuits. I'll have all my parts and equipment in to build my first cmoy in the coming weeks and I can't wait to get started.

 

[oxus]

Ah I see. Tangent's website has been a true help! I have been reading it to no end.. Good luck for your CMOY! I will wait patiently for my CMOY to come and start modding it probably. I will definitely try replacing the capacitors and maybe try different opamps to see how they sound.

 

[gimble]

Virtual ground in a standard CMoy should be coming from a voltage divider, not from the connection between the batteries. See schematic (PDF).
 
Taking VGND from the node between the batteries would indeed be a bad idea due to differential drain (and differential draw). If you're using 2x9V, the positive pole of the first should connect to the negative pole of the second and nothing else. The remaining terminals then become V+ and V-. Taking it from the voltage divider isn't perfect since it's an analog AC circuit, but it does the job for a CMoy-grade build.
 
Unless you have the prior audio and electronics experience to know better, you should really start with a standard CMoy and worry about advanced topologies later. Don't worry about things like virtual ground ICs until you've fiddled with the CMoy enough to start wanting a better amp - it's sort of pointless without changing a bunch of other stuff too, and more of a "two steps forward, one step back" solution anyway (refer to the virtual ground article). Walk first, then run.
 
CMoy is good for testing op-amps because it's such a simple design. There's not an overabundance of other factors to drown it out and it's as isolated as it's going to get. You should probably install an IC socket if you'll be doing much swapping. You might also want some Brown Dog SOIC adapters if you want to test chips which don't come in a through-hole package (SMD isn't terrible if you have appropriate tools e.g. a half-decent iron, soldering tweezers, braid, a flux pen). Caps wouldn't be a major priority for me though unless the existing ones are damaged or incorrect.
 
Also note that for diagnosis purposes you should really pick up a multimeter ASAP if you don't have one yet. If you want to do any soldering or circuit prototyping, it's absolutely essential. But a $12 POS special will be perfectly adequate until and unless you start using it very regularly.
 
Watch the Tangent Tutorials videos regarding soldering and multimeter use ASAP as well. They're good. Maybe the potentiometer video as well (it's more interesting than essential). The EAGLE videos can wait since you shouldn't be doing PCB design for a good while yet.