Active Headphone Splitter

[mutant_guitar]

I'm gonna be going on a trip in a month or two, and one of my friends is going to be bringing a portable DVD player for the bus ride. the problem is, i know that there will be at least four of us trying to watch it. the main problem comes in trying to share headphones. so, i want to build an active headphone splitter, seeing as i know running 4 sets of headphones from one jack won't work very well. i have a few questions i'm hoping you guys can help me with.

1. should i build it as a booster, or a small op-amp?

2. should i run the headphones in series or in parrallel?

i'm going to leave it mono, mainly because i don't want to have to build a circuit for each channel. also, it should be a low-drain circuit because i don't want to have to change batteries in the middle of the bus ride. the ride itself will be about 4-5 hours, so i'd like the circuit to last at least 6 hours on a 9v.

any idea, suggestions, or help will be greatly appreciated.

[cd]

Use a dual opamp, one side for each channel.  Use a unity gain buffer configuration, or a slight boost (1-2x gain).  Use an opamp with high current capability (like the 4558) and you should be able to drive four headphones easily in parallel.  Don't use a series configuration.

Alternately use a unity gain buffer feeding a transistor emitter follower, and use a high power transistor.

See this article for ideas:

http://headwize.com/projects/showfile.php?file=opamp_prj.htm