[Adol]

I built a CMoy following (more or less) Tangent's instructions, and it almost works perfectly.

I'm only having one big problem. I can't, for the life of me, figure out how to get this potentiometer to work with it. I've tried working it into the input a few ways, but the best I can do is get a buzzy, improperly-grounded volume control that can't even cut the output volume in half. Not good. I used a multimeter to determine which inputs have variable resistance between them, but something else is missing. :\

The entire amp is built from Radio Shack parts. Not great, especially the TL082CP op-amp, but, if nothing else, I figure that it's good practice before I build a nicer, fancier, harder-to-build, and considerably more expensive amplifier. And even this little low-end amp tightens up the sound from my computer a fair bit. Even if it makes the noise floor sound really really nasty in its current state.

The circuit mostly follows Tangent's recommended parts. I reduced the gain to 5.5x, used .22 µF caps in the amplifier section, and used the TL082 (bad, I know) op-amp in place of the OPA2132, though, and the supply voltage is 18 volts. I don't think that there's anything wrong with the main CMoy circuit, though. As I said, it works fine (albeit LOUD) with the potentiometer removed. No shorts, the positive and negative power supplies are very close in terms of voltage, and I cleaned most of the flux off of the board.

Any ideas as to how to get the thing to work?

Attached a few pics of the amplifier, and the pot. Sorry about the low quality;my camera hand's not the best for macro photography, and it takes a lot of compression to smush the pictures into <25k each. :\

 

[ECM]

i ran into similar problems when i built my first amp. i noticed in your picture that the potentiometer leads on one side are free from solder. in order for the pot to work, one side goes to the input signal, the other side goes to GROUND, and the middle is the variable output signal to the amp. same thing for the other channel. when i built my amp it was also loud as hell and the pot didn't do a thing until i grounded the other end. keep us posted on your progress.

-ECM

 

[tangent]

ECM got it right. To paraphrase: There are two groups of three lugs each. The middle is the "wiper" which is the output of the pot going to C1 on the amp. The outer pair are input to the pot and ground; if you hook them up backwards, the knob just works backwards from the way you expect.

 

[Adol]

Ah. I was only grounding one channel of the pot, which, I assume, is why it wasn't working properly. :\

Anyways, it works quite nicely now. Thanks for the help!

[size=xx-small]wow. this is kind of addictive.[/size]