First CMOY

OK, I'm no expert with electronics.  What little training I have was in digital circuitry, not analog circuitry.  So treat me like I know nothing, just to play it safe.  lol

Anyway, I got my amp all setup on a couple old protoboards I have from college. one board for the power circuit and the other for the amp.  I got everything wired up and plugged it into my computer and headphones.  I was happy to hear sound.

Well, really noisy... static-y... sound.

Couple of things you should know: this is currently driving a POS $30 Logitech headset, so the impedance is probably pretty non-existant, if that matters, I';m not using a basic CMoy setup, I changed out the 0.1uF input caps for 1uF caps and the 220uF power caps for 470uF caps.  Everything else remains unchanged.  I had planned to integrate a DC walwart as well, but that is not currently implemented.

Anyway, the sound was really bad.  I've been playing with grounding, but nothing has helped thus far.  I AM using the 47.5ohm resisters on the output.

Also, the power switch and volume pots are not tied into the circuit.  It's all direct.

The strangest part is that it honestly doesn't sound louder, even at full volume, than plugging the headphones into my computer directly.

If I unplug the circuit from the betteries, I still get sound.  Even though the opamp isn't powered.

Questions: I've obviously done something wrong powering the opamp: is that the cause of the noise?  Also, is my opamp in the john now that this has happened?

OK, I guess I posted too early.  Did a trace with my multimeter and found a V+ problem and a couple resister problems.  Getting clean sound now (except at high volumes, limitation of the headphones, I'm assuming.)  Sounds pretty damn good, with system volume down, this thing really pumps the db up a lot.  Keeps the sound clean, too.

Love it.

Yay!  All done!  Works great and no noise on the lines.  Made several mistakes along the way, soldering along, got quite a bit better at soldering (and de-soldering!) by the time I was done, fried one op-amp by putting it in upside down like an idiot... but all's well that ends well!  Glad I ordered two of everything, just in case.  lol

Now to make the second one, this time with the DC circuit added in.

Question: does the DC jack of two or three pins?  Is it V+, V-, and Ground or is it just V+ and V- that lead into the same voltage splitting circuit as the batteries?

If it's scenario two, then I just take V+ from the DC and tie it to the diode and then into the normal V+ circuit to be split, and the V- straight to the normal V- circuit, right?  I'm somehow willing to bet that that is exactly how it works, but with my newbishness I won't bet anything valuable... maybe a fried opamp.  xD

Hmmm... I wonder if there is anything I can do with an OPA2132PA that only has one channel.  lol  Seems worthless to me.  :)

Considering getting some more practice in and then attempting to change the opamps in my X-Fi.

http://a1.sphotos.ak.fbcdn.net/hphotos-ak-ash4/188964_196883336997534_100000276075241_664392_5466890_n.jpg

Yeah, the original plan was to use a larger plastic enclosure for a desk-amp version of the CMoy and the traditional mint-tin for a pocket version.  Of course you know how it goes, when the pinch came I just couldn't find either enclosure.  lol

So I scrounged up this old cardboard box.  I think it has a sort of... uniqueness to it.  :)

Anyway, yes, I used two 9v batteries, but they are connected in-line and then to a virtual ground (resister trick.)  So I would just divide the positive DC volts from the walwart and tie the other lead to ground.  I need to find a suitable walwart, though.  I was shooting for a 24v one like Tangentsoft's website listed, just have to find the right one.

I -think- I might benefit from using less gain, though.  I think 11 might be a waste.  We'll have to see once my 600ohm headphones come in.  I'm sure they will be significantly harder to drive than these Logitech pieces of crap.  :P

I'm looking at the rest of my parts now getting ready to start building a second CMoy tomorrow.  I plan on ordering an LME49860 opamp like what will be used in the X-Fi... I figure it would be worth a test run in the CMoy, just for fun.  (Actually the LME49860 is an 8-dip, I guess that the opamps needed in the X-Fi aren't, but there is a similar amp that is to be used.  EDIT: the LM4562s which are SOIC)

I wonder if it would be worth going up to 1000uF power caps or larger.  Is anything more than 1uF input caps necessary or worth it?  By my reading on Tangentsoft's website anything higher would show little to no extra improvement.  I keep on thinking of ways to improve on the circuit, but have little ability to get too creative.

Time to do more research.