Do laptops cause problems with CMoy

Hello,

I have completed my build of a basic CMoy which I have slightly modified. It's sitting on a breadboard right now while I tested things. I have a 24V DC power source which is regulated (makes it 23.7) and I have a TLE2426 rail splitter.

I've run into a curious issue which has me baffled.

With nothing plugged in, the voltage is split evenly as it should be (at 11.8 each). Using my laptop (an iBook) as a source, as soon as I plug it in the voltage gets really uneven. I can still hear sound, but one rail is at 19V instead of 11.8. The TLE gets extremely hot.

I thought this might be an issue with the TLE, or the way I wired it, so I took it out and replaced it with the standard voltage divider bridge. This was much worse, with voltage of 22V on one side.

I fretted until I walked over to my tv, rigged up a cable, and plugged into the audio out. Perfect. No imbalance at all! I haul out my portable stereo player and plug that in. Also perfect voltage balance between rails (constant buzz on headphones, but that's another matter I think). Plug back in my laptop - bang, uneven voltage.

Is there some property of laptops that cause them to do this? Do they already have an amp on-board? Does it matter if it's plugged in to the wall or running on battery power? Or is it just a curious quirk of my laptop and I should ignore it and solder up my amp?

Thanks in advance,

Jamdat

Quote:

Originally Posted by vixr 
thinking the same thing...try running the CMoy on a 9volt battery instead of the wallwart...

I tried this as one of my tests. Same thing. The battery read 9.16V and it was split equally with nothing plugged in. Plug in the laptop, and Vground to V- is now 8V and the other side is less than 1. This is actually what led me to suspect my source.
 

Quote:

Originally Posted by Pageygeeza 
Do a check on the voltages from the headphone jack of your lappy, put a load on it and measure it again.

I'm going to try this out now. Do you mean measure tip to ground and ring to ground on the jack alone? I don't have a tremendous amount of electrical knowledge, but this is the first thought I had.
 

Quote:

Originally Posted by cobaltmute 

You may have an issue in the way that the laptop is grounded.  If it is tied to earth, the headphone output ground may be tied to earth.  The output of the TLE may sit at a different potential, and it may be working hard to equalize the two.

I never thought of this. I figured the TLE was working very hard because it got very hot and the voltage difference was better than the simple resistor case. I figured that meant that it was trying, but failing.

I'll try plugging in my laptop for my next test. And I'll try the headphone jack on one of the other, desktop, computers in the house.
 

Thanks for the suggestions.