Here's the situation. I gave my roomate a sound feeder SF100 and a portable Philips Cd player so he can play CDs in his car (he only has the stock toyota cassette player). The way the SF100 works is:

* Hook SF100 to cigarette lighter for power
* Connect the SF100's power output to the CD player's DC input.
* connect the SF100's audio connector (regular headphone pin/jack) to the CD player
* Tune to an unused station on the FM band and voila!

Everything works fine and the SF1000 is great! However, the problem is that there's this background noise in the music with sounds like the CD spinning. It's specially worst when you pause the CD or while listening to soft music. It is really annoying.

I've done some experiments and found that if I power the CD player via batteries instead of using the SF100s power output, the noise goes away. So, this leads me to believe that it's the power source that's the problem or the CD player is not happy with the power specs of the SF100. What should I do to solve this problem? Is this a case of a grounds loop or just plain electrical noise? The only other think I haven't tried is another CD player cause I don't have one :-(

Thanks!

 

This definitely isn't a ground loop issue, as there's no true ground between the CD player audio section and the SF100. From the sound of it, the SF100 is outputting some really nasty DC power and you're running into some heavy electrical noise. The most likely culprit is crosstalk between the SF100's power cable (that's extremely noisy) and the audio section of the CD player.

 

Thank you MacGyver! It makes sense. So, is there anything I can do to filter this noise at the input or output of the SF100. I'm also going to try another CD player today to see how it deals with the SF100's power output?

 

Another thing you could try is temporarily powering the player with another cord, not the SF100, and see if the noise disappears or decreases. If it does, there's your answer, the SF100 and crappy filtering on the power line. If it doesn't, you're back to a couple of possible issues....noise coming in over the audio line from player to SF100, or noise internal to the SF100 cuasing problems, neither of which is going to be easy to remove. You can't put a filter between the player and SF100 because the frequencies you'd be blocking for the noise are most likely in the audible range (therefore, you'd be blocking out the music).

Another way you can tell if it's truly noise from the CD player's motor (which I highly doubt it is)...play the first and last track on a long CD. If the pitch of the noise doesn't change, the noise isn't from the motor controller.