[tangent]

The input impedance of the op-amp chip is on the order of megohms, which means that it's really easy to "drive" -- it requires very little current. This is good in some ways, but it also means that weak signals like radio interference can also drive the op-amp. R2 is in parallel with the op-amp's input impedance: 100K in parallel with "megohms" effectively equals 100K. In other words, it lowers the input impedance of the op-amp to make it less susceptible to RFI.

R2 is also in parallel with the pot's resistance, and it has the same kind of effect. If R2 isn't sufficiently large, as you rotate the pot's shaft the input impedance of the amp will shift. This can affect your source in small ways. It's a problem you should avoid, but it isn't likely to cause extreme bad sound.

If the sound is bad only when the pot is all the way down, and never at any other position, you've probably got the pot's wiper and input backwards -- swap the wire going to the input jack with the one going to C1. If I'm right, when the volume is all the way down, you're effectively grounding out your source in that configuration.

 

[nobody020]

Thanks Tangent for your suggestions and comments.

This is my current situation:
I swapped my original 10K pot that was working fine for a 50K pot, and now, the whole circuit is noisy, with or without source.

When I plug my PCDP in through an AC, the noise increases. If I turn the volume knob, the noise decreases as the pot goes to maximum volume (least resistance). If i touch any part of the circuit, the noise decreases.

Maybe I should just go back to that 10k pot. And my R2 is at 100K ohms..


-nobody020

 

[TaffyGuy]

i had this problem on my cmoy after resoldering the inputs/pot hookups so many times because of screw ups. its a ground problem which is why it changes when you touch it. you've got some bad solder spots i'd suspect, and i'd check the pot and the inputs/outputs first, becuase they're hardest to do generally. try just wetting all the solder spots, and make sure you don't short anything out by setting it in a metal case unprotected, anything like that.

i think it got loud right away because in the normal layout, where gain=11, thats REALLY HIGH for a stereo line out on efficient phones, and is meant more for a crappy weak output like a minidisc player or something. i'd suggest replacing (r3 is it?) the 1k resistors that go to ground from the feedback loop with 2k resistors if you have effecient phones.

good luck.