Earbud Adapter bare PCB and transformer supplied – $10
The #1 hardest and usually the most costly item to obtain in making a successful crystal radio for maximum performance, is a good set of sensitive high impedance headphones. This kit allows the use of common low impedance earbuds (like Walkman style) to work with high impedance audio output circuits found on crystal radios, without loading down the circuit resulting in loss of sensitivity or selectivity, (adapter impedance is 47K). Just plug in your inexpensive 3.5mm earbuds into the pcb and attach two wires from the adapter binding posts to the headphone connections of your radio. You will be amazed at the tonal quality and bass response. It is similar to the HZX Headphone Adapter featured in the article by the ARRL, but runs on a CR2032 coin battery and has adjustable gain. It can be easily moved from radio to radio. A long battery life, due to the very low current draw of the circuit. The pcb is just 2″ x 2 1/8″.
It is purchased as a bare board and transformer. You would need to source the easily obtainable components from Mouser and/or Tayda.
The tools required for the kit are a soldering iron with a small tip, rosin core solder, small side cutters, and can be built in less than an hour, depending on your experience. On a difficulty scale of 1 to 5, 5 being the most difficult, this is rated at 2.
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