On Mon, 20 Apr 2009 11:34:49 -0700 (PDT), David
wrote:

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

I assume you are talking about a broadcast receiver for frequencies
below 1600 kHz. At such frequencies and with a typical 500 pF variable
capacitor, the impedance levels for an LC resonant circuit is quite
high.

Loading it with a crystal detector and some low impedance (30 or less)
headphone will load the resonant circuit quite heavily, reducing the
output quite heavily.

In the old days, the typical impedance of a headphone might have been
about 2000 ohms, loading the resonant circuit much less. In order to
cause a similar loading to the resonant circuit using current
headphones, you need an audio transformer with 2000:30 impedance ratio
or 8:1 turns ratio.

Paul OH3LWR