[Andre Jute]

If your source puts out enough voltage to drive your headphones, you don't need an amp, all you need is a Passive Attenuator. It can be just a log pot in a box with sockets, or it can be a stepped attenuator built on a 24 step switch. The problem is usually calculating the resistors you need to make it work right. Now the recording engineer Iain Churches has published a spreadsheet to do the hard work for you:

http://www.kolumbus.fi/iain.churches...tenuators.html

You might also want to cruise the rest of Iain's impressive gear and schematics on his site: http://www.kolumbus.fi/iain.churches/

Cheers!

Andre Jute
Visit Jute on Amps at http://members.lycos.co.uk/fiultra/
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[koike]

Is it possible to attenuate the lower end rather then the higher end of the spectrum?

 

[Pars]

That would be a tone control, or filter, essentially.

To the OPs original point: Most "sources" don't put out enough voltage, or more importantly, current, to drive headphones (hence the popularity of amps). I'm not sure when you would ever want to attenuate the "headphone out" of a source... unless you are using really efficient earbuds or canal phones meant to be driven by an iPod or something like that. YMMV...