Lightbox circuit

[splitdog]

I built an online 5 channel lightbox. It works, but the input sensitivity control (pot) is scratchy when you turn it. I replaced it, and it is the same. The lights are affected, and the scratchy sound goes back up through the input into the stereo. The music crackles.
Also, if I leave the pot alone, it still sends crackling noise up through the input. There are 2 boards, the main, and the smaller input. The pot is on the input board. I am using the pre-amp outs as inputs. (line level). Any help would be greatly appreciated.

 

[sagor1]

Noise going back to the stereo may indicate improper grounding. Make sure all grounds are connected together between the lightbox and stereo. Don't rely on the LINE out shielding as grounding. I assume you did NOT install the MIC element, as that would pick up noise and just re-amplify it back into the lightbox. Also, make sure you have the AC Neutral properly identified and wired, along with a proper 3 prong plug that has the ground pin tied to the chassis ground.
Otherwise, your stereo's "line out" may not be well isolated. Try the lightbox with another music box of some sort (or laptop line out port), see if the noise follows the lightbox, or only happens with one of the stereo or other music device.
Otherwise, it may be hard to track this problem down. A good scope looking at the incoming signals through various stages would help to find the source of the noise.

 

[splitdog]

Thank you for your prompt reply.
I made sure to ground everything proper. I did not use the mic, or speaker options. Straight line-out to inputs. Neutral identified. When there is no music and I turn the input pot, I get the scratchy sound and the lights are effected. If I leave it, the crackling sound goes back up the input and I can hear it with the music. The crackling sound seems to 'go with the music'. So this is telling me something, I just don't know what. The lights are effected, too.

 

[splitdog]

"Make sure all grounds are connected together between the lightbox and stereo. "

The lightbox is grounded, and the stereo is grounded. They both share a common plug receptacle for AC.

 

[sagor1]

Try a different source of music, like your line out from a computer instead of a stereo. Try to isolate if the scratchy sound is due only by being connected to the stereo. If scratchy sound with the laptop as well, then something may not be wired right with the lightbox. If laptop is clear audio, then something is wrong with the stereo or its preamp output levels