Help Me diagnose my CMOY

[juniperlater]

Last week I built my first CMOY successfully. Now I just built another and it is really distorted.

Here is my first guess as to the problem, I removed the OPAMP off of a board from an old attempt at CMOY building, maybe I fried it while removing it?

My second guess is the way I jumpered the ground to a second section to make it easier for the mini-jack grounds to be attached.

Here is the pic:
Bottom:

Top:

 

[Pars]

What are the values of the R5 resistors (from pin 1 out an pin 7 out)? They look like they are more than 47 ohms. Anything higher than about 100 ohms here will cause massive distortion (color code yellow-purple-orange?)

 

[juniperlater]

I'll try that. I bought them as 47 1/4W, but I didn't check the color.

 

[juniperlater]

I am just going to jumper R5. That is the problem. Thank you. It was mismarked at the electronics store.

 

[Pars]

Yeah, that is what I would suggest if those aren't 47 ohms. I mistakenly put 470 ohm in the first two Cmoys I built, so I know that mistake well...

 

[juniperlater]

fantastic! It works great now. I got it mounted in the tin and it is great. I placed r5 in because of the first one having a low-level hiss (barely noticeable) and this one, also without r5, has the same hiss. However, once the volume outdoes the hiss, it sounds beautiful.

 

[Pars]

Dropping the gain is usually more effective in dealing with hiss. The stock gain of 11 is really high for almost all cans. If you are using really efficient cans, reduce the gain. I always built mine with a gain of 5.5 (IIRC), 10K R4 and 2.2K R3 (think I got the resistor numbers right), but basically increase the 1K stock R3. Gain formula is 1 + R4 / R3 (again, adjust if I have the resistor numbers wrong from memory).

 

[juniperlater]

Great idea! These are the things I need to learn. The gain is REALLY high. I need to do the math. Thanks again.

 

[n_maher]

Like Pars said, drop the gain way down and you'll likely be fine without R5. Personally for all my portable amps I run a gain of 2 or 3. Sure, you have to crank the knob depending on what headphones you're using but that's what it's there for, right?!?!

Nice catch on the resistor Pars, that's some good sleuthing.