David wrote:
Looking for Crystal Radio Receiver Circuits, that have a voltage
quadrupler to increase headphone volume without batteries or AC power.

If you are quadrupling the voltage at the headphones, then you are, of
necessity, dividing the impedance at the detector by a factor of 16.

You only have so much power available at the antenna; a detector
followed by an unpowered "voltage quadrupler" won't extract any more
power than any other equivalently-well-matched detector, and so won't
put any more power to the headphones.

If you really want to do this passively, and not rely on some near-by
strong station for power, then you need to optimize your circuit and
headphones for efficiency, and you need to get a _lot_ of wire into the air.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" was written for you.
See details at http://www.wescottdesign.com/actfes/actfes.html