There are many different model of David Clark headphones. Mono, Stereo, Volume control, microphone, plug style, head-strap style...
I bought my DC H10-C on eBay for around $45. The are the ultra-plain-jane model. Mono headphones w/ normal 1/4" jack, no volume control, no microphone. I love them. Excellent audio response for voice communication, and excellent at muffling ambient noise like computer fans, the XYLs vacuum cleaner, and screaming children.
I did find this for you.... schematic for one of the fully loaded models.
[LEFT][FONT=Tahoma][COLOR=black]"Ham Radio does not abide by the [B][COLOR=darkgreen]'Right Tool for the Job'[/COLOR][/B] rule. Quite the contrary.[/COLOR][/FONT][/LEFT]
[LEFT][FONT=Tahoma][COLOR=black]It often gets the job done with things you wouldnt normally recognize as tools."[/COLOR][/FONT][/LEFT]