Cmoy troubleshooting
Sep 25, 2006 at 11:33 PM Thread Starter Post #1 of 12

xelion

Head-Fier
Joined
Mar 13, 2006
Posts
63
Likes
0
Okay, well I first had a problem with my power supply section, all the voltage was going to one side, but I got that fixed by cleaning up the soldering point on the back, so now it sounds through both phones, but the sound is really quiet, even with the pot turned all the way up and my player all the way up. It also sounds fine at low volumes, but as you get much more than a quarter turn on the pot the sound gets badly distorted.

So any ideas what may be causing this, let me know what to measure and i'll give you the values and all.

edit: see last post for my most current problem
 
Sep 26, 2006 at 12:04 AM Post #2 of 12

xelion

Head-Fier
Joined
Mar 13, 2006
Posts
63
Likes
0
Okay, I fixed that problem, I realized that I forgot to attach the power to my opamp in my haste. But now I have another problem. There is a hiss in my headphones when they are connected, and they get very loud and distorted when sound is applied.

Any ideas?
 
Sep 26, 2006 at 1:10 AM Post #3 of 12

civilmonkey

100+ Head-Fier
Joined
Feb 17, 2006
Posts
126
Likes
10
More information always helps... What schmatic and opamp did you use?

Double check your work and soldering. Make sure there are no cold joints or solder bridges. Also, make sure you've cleaned the flux residue off your board. This link: http://tangentsoft.net/audio/trouble.html has some great ideas as well.

If this doesn't work, posting high resolution pictures of the top and bottom of your board will help people see what might be wrong.

Good luck!
 
Sep 26, 2006 at 1:21 AM Post #4 of 12

xelion

Head-Fier
Joined
Mar 13, 2006
Posts
63
Likes
0
Well the schematic, I used pretty much the basic cmoy amp from tangentsoft, I think the only thing I changed one of the capasitors to 470uf instead of the 220 and I used a 2.5k resistor for a gain of 5. I didn't put the R5 in, and I used the opa2132pa opamp.

I'll try to get some pictures up later...
 
Sep 26, 2006 at 2:31 AM Post #5 of 12

xelion

Head-Fier
Joined
Mar 13, 2006
Posts
63
Likes
0
Well I don't know what I did, but I fixed the distortion problem. But I created yet another problem. I get almost no sound out of my right earbud. It's not the phones beucase they work fine with out the amp, and it does the same thing with my other pair.

I've replaced a resistor on the board, should I go ahead and replace all of them and the caps as well? On just the right side?
 
Sep 26, 2006 at 3:19 AM Post #6 of 12

xelion

Head-Fier
Joined
Mar 13, 2006
Posts
63
Likes
0
okay, last problem.

I figured out, I messed up when putting the resistors in, I had them one row up on the right side, so I got that, it sounds great, but I get a slight buzzing sound when the pot is slightly above minimum for about an 1/8-1/4 turn then it goes away. It only comes if i'm touching the case, so I'm pretty sure it's a grounding problem. But I was always confused on that part.

Do I have to have a wire going from the groud touching my case? Because as it is right now, I have some electrical tape on the bottom to prevent the solder points from touching and causing a short. The two rows for ground that Tangent provides aren't touching anything but the wires that are connected to it.

edit: Okay so I've thought about it, and I think it might also be the resistance. Would adding an R5 help? As in Tangents article I went with jumpers in place of R5. What about a lower gain? As I stated above I used 2.5k resistors, for a gain of 5 I believe, would a gain of 2 or 3 be better? It doesn't always have the noise. I have a 50k pot in, instead of the suggested 10k on Tangents article, would lowering that help? Or what about bumping it up to a 100k pot? Would that be better? Also I notice that when the pot is turned low I can hear the sound even when i'm not touching it, but when I turn it up more, it goes away, unless I touch it, and it's still very faint, that's what led me to believe it might have been the resistors that were the problem.

If anyone could give me some insight, I'd be happy. I'm already loving the cmoy, even with it's buzzing, it makes the music sound so much fuller.
 
Sep 26, 2006 at 11:50 AM Post #7 of 12

tomb

Member of the Trade: Beezar.com
Joined
Mar 1, 2006
Posts
10,535
Likes
761
If the buzzing goes away when you touch the pot, it's a grounding issue. Usually, the barrel of the input/output jacks are connected to the case (metal to metal). None of the other things you mention would cause a buzzing.

Your question about the pot resistance affects R2, not R5. R2 should be 10X the resistance of the pot. For the standard CMoy, R2 is 100K ohm (10 x 10K pot = 100K ohm). If you use a 50K pot, then R2 should be at least 500K ohm. That could introduce noise if that resistor is off, but it would probably be in the form of a hiss, not a buzz.

The only other possibility is some noise from the pot's wiper in the low volume setting. That would be more of a scratching sound, not a buzzing, though.

I vote for the grounding issue. If your jacks do not have a metal barrel, or are isolated so that metal doesn't touch metal, then I'd run a wire from the pot's grounds to the case.
 
Sep 26, 2006 at 12:21 PM Post #8 of 12

xelion

Head-Fier
Joined
Mar 13, 2006
Posts
63
Likes
0
The buzzing doesn't go away when I touch it, the buzzing starts when I touch it.

My in/out jacks are plastic, but I have a ground wire running from the ground to the virtual ground on my board.

So get some higher resistors and/or a new pot?

I'll try running another ground wire from my pot straight to my case, see if that helps any.
 
Sep 26, 2006 at 12:31 PM Post #9 of 12

xelion

Head-Fier
Joined
Mar 13, 2006
Posts
63
Likes
0
Well the wire fixed the buzzing, but when I'm turning the sound sometimes I will get a slight scratching sound, that is the pot? Or R2? I'll stop by radioshack and get some higher resistors after school today and see if that fixes that.
 
Sep 26, 2006 at 2:00 PM Post #10 of 12

tomb

Member of the Trade: Beezar.com
Joined
Mar 1, 2006
Posts
10,535
Likes
761
Scratching is a dirty pot. This can often happen if some flux gets inside the pot from soldering the pins. Spray some flux or contact cleaner inside, or pour some pure alcohol down into the pot (through the pin outs) and blow it dry with a can of compressed air. Rubbing Alcohol is ok if you use some 91% or purer.
 
Sep 26, 2006 at 10:53 PM Post #11 of 12

xelion

Head-Fier
Joined
Mar 13, 2006
Posts
63
Likes
0
Okay, well I stopped by rat shack today, got some more resitors, I got 470k ohm and 1mill ohm because I wasn't sure if 470k would be close enough to 500k for it to be fine or what. Would using 470k or 1mill be better? Is 1mill too much?

I'm going to do that rubbing alcohol thing and see if that fixes it. Thanks for the help.
 
Sep 27, 2006 at 12:11 AM Post #12 of 12

Pars

Can Jam '10 Organizer
Joined
Oct 28, 2003
Posts
4,127
Likes
55
Quote:

Originally Posted by tomb
Scratching is a dirty pot. This can often happen if some flux gets inside the pot from soldering the pins. Spray some flux or contact cleaner inside, or pour some pure alcohol down into the pot (through the pin outs) and blow it dry with a can of compressed air. Rubbing Alcohol is ok if you use some 91% or purer.


Do you have input capacitors on this? Scratching can also be caused by DC on the pot.
 

Users who are viewing this thread

Top