[barkas]

I built a pretty standard CMOY, first on breadboard, then I made my own PCB (a pretty nice one, too

) for it. OPA2132 and all the values in the schematic by tangent. I used 1% metal film resistors and matched them most carefully as well as my multimeter can, to 0.1% usually.

So, now when I have no source connected, the amp hums, not excessively, but it's a bit noisy, as soon as I connect a source (ipod), the humming goes away.

That was the simple one, or the one I can live with.

Then, despite my resistor matching, the left channel is a little bit louder than the right one. I verified that it's not the headphones nor the source doing that.

I use input capacitors at 0.1uF that look like this one:

and 220uF electrolytic capacitors for the power supply.

 

[tangent]

Check your grounding. If the grounds look okay, then I would make sure you don't have a soldering problem, perhaps due to a combination of impatience and large ground planes.

 

[barkas]

An update:

The AC part of the output has no measurable difference with my means, well, maybe 1mV at 170mV signal level.
But the DC output is 1.6mV for one channel and 6.6mV for the other. Can that be heared? And what do I do about it?

 

[tangent]

Quote:

Originally Posted by barkas But the DC output is 1.6mV for one channel and 6.6mV for the other. Can that be heared? And what do I do about it?

A small amount of DC offset is normal, and harmless.