DIYbanter - Whats the difference between Magnetic & Crystal headphones?

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Whats the difference between Magnetic & Crystal headphones?

Whats the difference between Magnetic & Crystal headphones?

I have an old tube tester which has a jack labeled "NOISE"
I downloaded a manual for it and it says that is to hear noisy tubes.
Then it says use MAGNETIC headphones, crystal headphones will NOT work.

I wont likely ever use this function, but I am curious......

My guess would be "magnetic" phones would have something like a speaker
in them, and that all modern phones are made this way. (just a guess).

So what is a crystal headphone and how does that work?

Whats the difference between Magnetic & Crystal headphones?

On Friday, 28 December 2018 03:12:00 UTC, wrote:

Whats the difference between Magnetic & Crystal headphones?

I have an old tube tester which has a jack labeled "NOISE"
I downloaded a manual for it and it says that is to hear noisy tubes.
Then it says use MAGNETIC headphones, crystal headphones will NOT work.

I wont likely ever use this function, but I am curious......

My guess would be "magnetic" phones would have something like a speaker
in them, and that all modern phones are made this way. (just a guess).

So what is a crystal headphone and how does that work?

magnetic are either moving coil or moving iron. Google can soon explain how piezos & crystal earpieces work.

NT

Whats the difference between Magnetic & Crystal headphones?

On Thursday, December 27, 2018 at 7:12:00 PM UTC-8, wrote:
Whats the difference between Magnetic & Crystal headphones?

Magnetic headphones (like most earbuds) are low-impedance and have DC
conductivity. Crystal headphones are high impedance (and are capacitive,
kind of like a capacitor microphone in reverse), so have NO DC conductivity.
The likely reason to use magnetic is that a DC path to ground is required
to correctly bias some amplifier stage.

Absent a DC path to ground, some tube-type equipment outputs hundreds of
volts, could be hazardous.

Whats the difference between Magnetic & Crystal headphones?

On Friday, 28 December 2018 06:04:14 UTC, whit3rd wrote:
On Thursday, December 27, 2018 at 7:12:00 PM UTC-8, wrote:

Whats the difference between Magnetic & Crystal headphones?

Magnetic headphones (like most earbuds) are low-impedance and have DC
conductivity. Crystal headphones are high impedance (and are capacitive,
kind of like a capacitor microphone in reverse), so have NO DC conductivity.
The likely reason to use magnetic is that a DC path to ground is required
to correctly bias some amplifier stage.

Absent a DC path to ground, some tube-type equipment outputs hundreds of
volts, could be hazardous.

Moving iron headphones were originally in the 1-8k ohm range, modern ones mostly 32 ohms. Crystals are odrers of magnitude higher impedance, much greater efficiency & dire sound quality. A DC path can be added using a resistor or choke.

NT

Whats the difference between Magnetic & Crystal headphones?

http://www.circuitstoday.com/wp-cont...uit-Symbol.jpg

http://www.circuitstoday.com/wp-cont...uit-Symbol.jpg

I have generally found it useful to give a picture along with an explanation - it makes the jargon more grounded, pun intended.

Top picture is a Piezo (crystal) transducer symbol. In the simplest of terms, bend a crystal, it will emit electricity. Apply electricity to a crystal, it will bend. But, as you may see from the symbol, there is no direct connection between the two poles of the transducer.

A magnetic speaker, whether PM or Field Coil uses a voice-coil that is moved by changing AC voltages applied to the voice-coil. So the two poles are directly connected via the voice-coil. Yes, there is DC continuity - and as a rule, magnetic speakers do not like DC.

That the tube tester wants magnetic headphones indicates that it is a low current output device. Given that most tube testers - pretty much a done-deal after the 60s by way of design improvements - have no formal amplification built in, a magnetic headphone makes more sense. What the "Noise Tester" is measuring is a sample from the anode load resistor and amplifying the output to a speaker (or eye tube) - depending on the manufacturer.

Some testers have settings for this test that more resemble actual operating conditions, rather than "full throttle current" as typically done for life-test.

The above few lines from "sample" through "Life-test" are quotes.

http://www.john-a-harper.com/tubes201/#Noise

However, there are all kinds of noise - usually in very small values.

Peter Wieck
Melrose Park, PA

Whats the difference between Magnetic & Crystal headphones?

Look165 wrote:

One works with electromagnetic force, the other works with piezoelectric
force.

The first is low impedance and good for low frequencies,

** The two facts are not related.

The other is high impedance and good for high frequencies, it uses voltage.

** See above.

With a typical 8-Ohm or 32-Ohm output, the crystal headphone is useless.

** Utter nonsense.

In the 1960s, transistor radios and came supplied with crystal earpieces.

..... Phil

Whats the difference between Magnetic & Crystal headphones?

On Friday, December 28, 2018 at 10:51:50 PM UTC-5, Phil Allison wrote:
In the 1960s, transistor radios and came supplied with crystal earpieces.

.... Phil

Those crystal diode radios we all built when I was a kid needed those earpieces. Had to wind wire on a tube, etc.

Now kids are probably doing SDR instead, at least the nerdy ones.