Will CD or Preamp to drive Headphones?


I have read that the output impedance of most cd players is on the order of a few hundred ohms. If my headphones have a similar impedence rating, is there any reason I can't simply connect them via an adapter to the RCA output jacks on my CDplayer? Or, if using a cd that doesn't have a digital volume control, what about connecting the headphones directly to the variable outs of the Preamp? would this be different for a tube preamp as opposed to a ss one? There must be a reason why people (including myself) buy separate headphone amps... On the flip side, I have used my headphone amp (earmax) as a preamp - the sound was very bright with seemingly exaggerated bass. I would appreciate it if someone coud shed some light on the technical differences betweeen Preamp and headphone amp output and the feasibility and/or risks of interchanging them.Thanks!
timvis
Don't know, but I suspect you are correct about wanting to match impedances. But when I was reading the review for the Musical Fidelity A3CR preamp, the reviewer was lamenting the fact that it wasn't set up with a headphone amp, as it (paraphrasing) should have been adequate, what with roughly 3 Watts of gain (going from memory, so feel free to correct). So sometimes they can, but I wouldn't try it unless I knew what I was doing...
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