Amplifier or DIY earphones for crystal radio?

Thread Starter

bypassrestrictions

Joined Jun 1, 2021
32
I want to make a crystal radio to listen to frequencies outside of AM band(below 540KHz and above 1700KHz), asking this on reddit I was told, I need to add more turns to the coil and use a larger variable capacitor. Even if I assemble this, I don't have a suitable earphone to listen to the music.

So my problem now is to either amply the signal or create an earphone with high impedance, I'm unable to buy such an earphone and they are not sold where I live.

Is there a way I can amplify the output or create high impedance earphones by modifying already available earphones? Or can I just connect the output of the crystal radio into a any speaker with 3.5mm input?
 

MrChips

Joined Oct 2, 2009
23,528
Welcome to AAC!

The idea behind the crystal radio is to be able to receive and listen to radio stations without using any additional power source. The power received is very low and will not be high enough to power a loudspeaker. You need a high impedance headset (greater than 10,000 ohms) or an piezoelectric earphone.

If you are going to use a powered amplifier then you may as well use a transistor radio.
If you want to go with a sustainable energy source you can use rechargeable batteries that are charged by solar panels during the day.
 

Thread Starter

bypassrestrictions

Joined Jun 1, 2021
32
Welcome to AAC!

The idea behind the crystal radio is to be able to receive and listen to radio stations without using any additional power source. The power received is very low and will not be high enough to power a loudspeaker. You need a high impedance headset (greater than 10,000 ohms) or an piezoelectric earphone.

If you are going to use a powered amplifier then you may as well use a transistor radio.
If you want to go with a sustainable energy source you can use rechargeable batteries that are charged by solar panels during the day.
Thanks for the welcome.

Piezoelectric earphones are not available here and I can't buy from outside. Off the shelf transistor radios have limited frequency range, that is why I'm considering building my own crystal radio or can I build my own transistor radio?
 

Thread Starter

bypassrestrictions

Joined Jun 1, 2021
32
I can show you how you can amplify the signal from a crystal radio.
What transistors do you have?
What radio station frequencies are you interested in receiving?
I don't have any transistors.

I don't know about any radio station frequencies in AM, this would be the first time I'll be listening to AM radio, so that is why I want to receive below 540KHz and above 1700KHz, including everything in between.
 

MrChips

Joined Oct 2, 2009
23,528
I don't have any transistors.

I don't know about any radio station frequencies in AM, this would be the first time I'll be listening to AM radio, so that is why I want to receive below 540KHz and above 1700KHz, including everything in between.
AM broadcast frequency band is about 540kHz to 1700kHz. Why do you want to receive outside of that band?
 

Thread Starter

bypassrestrictions

Joined Jun 1, 2021
32
AM radio and short wave radio produce terrible sound quality. An FM radio produces music fairly well.
A crystal radio has terrible performance. A real radio has good performance.
Why do they produce terrible sound quality? Is it the bandwidth problem or something else? What is a real radio, the one with batteries?

AM broadcast frequency band is about 540kHz to 1700kHz. Why do you want to received outside of that band?
Out of curiosity.
 

sparky 1

Joined Nov 3, 2018
543
Some practical fabrication techniques to building a high quality crystal set are illustrated on this link.
You might find a blocking capacitor in schematic, both the 1.)earphones and the 2.) blocking capacitor form a filter that separates the audio from the carrier having done that some amplification can improve the audio amplitude. Better on the ears.
In the configuration called "modified mystery" different combinations have been tryed with earphones good combinations.
The large tuning coils can have taps for going outside MW. When you switch the coil you also want to get close to Xl=Xc with the adjustable capacitor.
To go further the antenna gain and higher Q coils such as spider web coils have been successful.
Care in reducing hand capacitance and better use of ground with dielectric is illustrated black melamine being adequate.
Learning radio in less than perfect reciever has the advantage being able to listen and interpret weak signal like learning the skills
of snow skiing compared to only driving a snow mobile.
http://www.alvenh.com/misc-projects/crystalset/
 
Last edited:

Audioguru again

Joined Oct 21, 2019
3,188
Why do they produce terrible sound quality? Is it the bandwidth problem or something else? What is a real radio, the one with batteries?
The AM broadcast system was designed 115 years ago when any sounds were better than no sounds. AM (means amplitude modulation) picks-up amplitude interferences like car spark plugs, electrical switches, electric motors and distant lightning.
The stations are 10kHz apart so the radio must filter away frequencies above about 2.5kHz to avoid interference between stations. We hear 6.7 times higher to 20kHz. A half-decent FM radio produces sounds to 15kHz.

A crystal radio has only one LC tuned circuit and no electronics. It picks up a few strong local stations at the same time.
Its sensitivity is poor and strong local stations sound loud and weak distant stations are barely heard.

A real AM radio has at least 5 LC tuned circuits for good selectivity and a radio frequencies amplifier with automatic gain control so that a weak distant station is as loud as a strong local station. It still produces all the clicks and buzzing from Amplitude interference. It still cuts all high audio frequencies but some new AM stations boost sounds from 2kHz to 4.5kHz to sound a little less muffled.
 

SamR

Joined Mar 19, 2019
3,409
With a crystal set you get everything hitting the antenna. A lot of noise and hopefully some signal. There is no squelch, and the bandwidth is pretty loose, so noise is a problem unless you have a broadcast station nearby, and a really good semi directional antenna is always better to pick up signals.
 

LowQCab

Joined Nov 6, 2012
552
With a Crystal-Set it's ALL ABOUT THE ANTENNA, and an excellent Ground-System.
This is where the (weak) Power comes from.
Longer and higher is always better,
make your Antenna as long, and as high above the ground, as you can possibly make it.
 

SamR

Joined Mar 19, 2019
3,409
The long wire is the "classic" crystal radio antenna. Basically as much wire as you can string as high as you can string. Better and even directional is the Loop Antenna which can be built on a square frame 1 meter on each side is more compact it is also directional. Crystal Radio is something very simple that folks take on as much for radio as for craftsmanship which can be truly a work of art. Here is one simple link to give you a taste: Getting Serious About Crystal Radios | Hackaday

Grounding has been mentioned and is important for all radios. I have a through-window wooden bar with 6 coax connectors and 3 insulated stud connectors plus a ground connection and a grounded plating on the external and internal faces of the bar that grounds all the coax external sheaths. Below the window is a 10' 3/4" copper clad steel driven ground rod with bare #10 solid copper wire that connects to the pass through plate and is terminated inside the window to a ground buss. All of my radio chassis' are connected to this ground buss. Additionally there are lightning suppressors/spark gaps grounding each antenna coax outside that connects to the driven ground rod to try and keep lightning out of the house. No guarantee but one can only hope not to suffer a direct stroke of lightning on an antenna and hopefully ground any ESD energy induced into the external antenna from nearby lightning strikes. All antennas use ground as the counterpoise to the active antenna and a dedicated ground rod is the best solution.

Some folks get real serious about building crystal radios and they range in style from the simple foxhole/rusty razor blade to very well crafted pieces of functional art. Can't find the link but there is a yearly build competition that contenders turn in some beautiful pieces for yearly.
 
Last edited:

DickCappels

Joined Aug 21, 2008
7,434
This simple AM receiver covers 480 kHz to 1.5 MHz and by switching in a fixed capacitor changes the tuning range to 179 to 181 kHz for listening to Lowfer transmitters. If you don't already know the ZN414, MK484 and related one chip TRF (Tuned Receive Frequency) receivers you should have a look. Plenty of gain + AGC in a three pin receiver.

1622613681379.png

Note the single transistor earphone amplifier.
 
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