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I'm attempting to build a crystal radio according to the following schematic:

enter image description here

Rather than attaching a piezo electric earphone as shown, I would like to hook the radio up to a stereo amp using a 3.5 mm jack. Where should each wire be attached to on the headphone jack?

I'm not 100% confident that the picture of the headphone jack is the correct one, but it looks like the one I have.

WHY
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2 Answers2

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You would connect the ground from your radio to the ground pole of the connector - that would be the ring closest to the plastic body of the plug. The speaker connection from your radio would go to either of the otehr rings - it doesn't really matter which.

This may not work. The output of your radio will be very high impedance (it will act like there's a big resistor in the speaker output.) If the amplifier input is too low impedance then it will act like a short circuit to the radio's speaker output and you won't hear anything.

Also, I hope you live close to an AM radio station. I tried several times as a teenager to build one, but could never get them to work. We lived in the boonies, way far away from anything. When I moved and got closer to a transmitter, I found it much easier to get a crystal radio to work. If it doesn't work at all, you might need a much bigger antenna.

I would suggest getting a proper crystal radio earphone and testing it that way first, then moving to an amplifier later when you know the radio works.

Given that you are planning to try this with telephone wire instead of the magnet wire generally used, I would really, really, really suggest you try it with a crystal radio earphone first. You've got enough variables to deal with already. Adding the amp just adds more things to go wrong.

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JRE
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  • Thanks, JRE. I ditched the phone wire idea. I'm now using 22 guage hookup wire. I purchased a piezo buzzer just in case the amp doesn't work. For the buzzer, can I plug it straight in, or does it need to be modified? It has two wires already. – WHY May 22 '15 at 06:56
  • Damifino about the buzzer. Radios of the type you are trying to build are difficult enough to get running when you do everything right. Every change you make just makes that much less likely for it to work. A crystal radio earphone is cheap, and is the right part. Magnet wire is also the right thing to use, not 22 gauge plastic insulated copper wire. The insulation may (or may not) change the characteristics of the coil, so the coil may (or may not) work. Build a radio strictly by the plans, then when it works you can start experimenting. – JRE May 22 '15 at 06:58
  • I believe its the same crystal piece used in the crystal radio earphone you see online (apparently they're all the same). I'll post a picture for comparison. – WHY May 22 '15 at 06:59
  • This gentleman creates a crystal earphone from the buzzer.[" DIY Crystal Earphone for Crystal Radio" https://www.youtube.com/watch?v=k3HsVlxR2tA] Only, he attaches a 3.5mm headphone jack to it. I'm fine with just plugging it in directly into the circuit, but I'm not sure if I still need to make any modifications. – WHY May 22 '15 at 07:01
  • Got the radio to work with the amp! Thanks, JRE! Now you've got me curious about the Piezo earphone. – WHY May 22 '15 at 07:30
  • Congratulations! – JRE May 22 '15 at 07:36
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you just need a 10k:2k transformer (for impedance matching) at the earpiece with the secondary to the audio amp.

AA9GG
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