Crystal Radio / Piezo Earpiece Interfacing

Here's how to interface a piezo earpiece with a crystal radio.

Parallel-tuned, series-fed radio:

The earpiece is interfaced through a 33 kΩ shunt resistor. The resistor provides a path for the
detector current. The voltage drop across the resistor drives the earpiece.

Series-tuned, shunt-fed radio:   
   

The earpiece is interfaced through a 2.5 mH RF Choke to prevent its capacitance from short-circuiting the detector. The voltage drop across the detector drives the earpiece.

Related post: Makeshift Piezo Earphones
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Ideal detector for a Shunt-fed Crystal Radio

A Germanium transistor may be configured as a diode, having its forward voltage as low as 0.1 V, by just interconnecting its base and emitter.

Basic Shunt-fed Crystal Radio

It makes for an ideal detector in a shunt-fed crystal radio.

Related post: Crystal Radio Circuits - Alternative Concepts
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