by TomMcNally » Thu Sep 09, 2010 12:49 pm
Typically, you can just connect a 1/4" headphone jack to
the speaker terminals, usually with 100 ohm 1/2 watt or 1 watt
resistors in series with each "hot" terminal.
If you have headphones with very high sensitivity, over
100 db or so, you may want an amp designed specifically
for headphones, with much lower noise.
But for normal phones, you should be good.
... tom