"Trevor Wilson" wrote in
message
As you correctly surmised, most non-headphone amp
equipped amplifiers use a 220 - 470 Ohm series resistor
to limit power to the headphones.
So far, so good.
What you may not know
is that most headphone amp equipped amplifiers use
similar value resistors in series with very cheap OP amps
to drive headphones.
Wrong. Most op-amp based headphone amps use far lower value resistors, for
pretty obvious reasons. They'd have to use a far more expensive op amp and
power supply if they used such a large resistor. Series resistors are still
often used, but they are usually of a far lower value, for example 10-50
ohms.
http://www.rane.com/pdf/hc4sch.pdf
http://www.rane.com/pdf/hc6sch.pdf
http://www.rolls.com/data/ha43man.pdf
http://www.headwize.com/projects/cmoy2_prj.htm
http://www.minidisc.org/schem.gif
http://sound.westhost.com/project109.htm
This is just plain daft. Headphones,
like speakers work best when sourced from a low impedance
source.
Agreed.