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CMoy unbalanced volume

post #1 of 10
8/1/11 at 12:05am
Thread Starter 


So I built my first amp and I am having a little trouble. One channel is louder than the other.



 



It worked on the breadboard, no issues, I did not check for equal volume on each channel.



Now that it's on the pcb (homemade), I notice that it is slightly louder on the left side. I have checked all of the solder joints, and they are solid (but dissorganized)



 



So is there a way to fix this? I checked resistance on each resistor, and both gangs of the pot are equal.



do you know what my issue is? I did clean the flux away. and I tested on another opamp as well, and the same thing happens.



Edit: and I did also try different headphones, and made sure it wasn't my ears
Edited by Legot - 8/1/11 at 12:14am
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post #2 of 10
8/1/11 at 6:46am

If you have a volume pot, check that to make sure the resistance is the same on left and right channels.  I've had cheapo pots that were as much as 20% different from left to right.

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post #3 of 10
8/1/11 at 7:04am
Quote:
Originally Posted by frijones View Post

If you have a volume pot, check that to make sure the resistance is the same on left and right channels.  I've had cheapo pots that were as much as 20% different from left to right.


Its not so much resistance as it is attenuation. 

 

If you are not spinning the pot up about 1/4 of the way or more channel matching probably sucks a lot. Reduce the gain of the amp until you can do that. 

 


Edited by nikongod - 8/1/11 at 7:22am
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post #4 of 10
8/1/11 at 4:17pm
Thread Starter 
I forgot to mention this earlier, but My gain is at 2 (as opposed to tangent's 11). And id did double check the pot values, and they are dead on equal.

I don't know if this matters (I don't see why it should) but the power circuit is TLE2426 based.
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post #5 of 10
8/1/11 at 5:12pm

Do you have a source with digital volume control?

 

Set the digital volume control fairly low (like -40db) and turn the analog pot up way high.

 

Is it still unbalanced L-R?

If the image "centers" as you turn the volume up its the pot. 

If it is still unbalanced, thats weird! I would make triple sure that your gain resistors are the same channel to channel. If you used 5% tolerance resistors (or worse) to set the gain measure the actual values and do the math. a ~5% difference in gain is audible and 10% is obvious. 

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post #6 of 10
8/1/11 at 5:48pm
Thread Starter 
Quote:
Originally Posted by nikongod View Post

Do you have a source with digital volume control?

 

Set the digital volume control fairly low (like -40db) and turn the analog pot up way high.

 

Is it still unbalanced L-R?

If the image "centers" as you turn the volume up its the pot. 

If it is still unbalanced, thats weird! I would make triple sure that your gain resistors are the same channel to channel. If you used 5% tolerance resistors (or worse) to set the gain measure the actual values and do the math. a ~5% difference in gain is audible and 10% is obvious. 


It is wierd! tongue.gif It's still unbalanced when I run it from my computer at low volume (2%) and it doesn't even out either, and on my meter, the resistors all read out the same before placement, and they are indeed the same resistance, each of them 1.2k 0.5w +/-2% (quite large, I know). I don't know if this is odd or not, but when I measure them individually on the amp, they all read half their resistance(0.6k), I expect this to be normal.


If I never find a solution, than so be it, I'll build more, better amps later on biggrin.gif
Edited by Legot - 8/1/11 at 5:56pm
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post #7 of 10
8/1/11 at 7:36pm

Have you tried different sources?

Or use your existing source but hook up just one channel (L or R) from the source to both amp channels.

You would want to make sure the imbalance is in the amp or if it's occurring prior to it.

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post #8 of 10
8/1/11 at 9:15pm

bypass pot with some wires temporarily to check if it is the problem

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post #9 of 10
8/2/11 at 11:17am

op amp might be faulty

do you have 2 chips or one dual one?

try swapping the inputs to the positive inputs of the op amp

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post #10 of 10
8/2/11 at 10:39pm
Thread Starter 

Bypassing the pot didn't help with the balance, swaping inputs would be more trouble than I'm willing to make with this one.

 

It is my first, of course it will have problems, I was able to remedy the situation by adding a pot between the two output sides of the pot, and now I can manualy control balance. That will do for me.

 

Thanks for your help guys! :) I will be building my next amp sometime soon, hopefully something more complicated. I won't ask for suggestions, I found this thread

http://www.head-fi.org/forum/thread/537398/list-of-diy-headphone-amplifiers

I'll do my own research ;)

 

Thanks again!

 

I'll be asking more questions eventualy ;)

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