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Whats the difference between Magnetic & Crystal headphones?

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Guest

Fri Dec 28, 2018 4:45 am   



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?


Guest

Fri Dec 28, 2018 4:45 am   



On Friday, 28 December 2018 03:12:00 UTC, tub...@myshop.com wrote:

Quote:
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

whit3rd
Guest

Fri Dec 28, 2018 7:45 am   



On Thursday, December 27, 2018 at 7:12:00 PM UTC-8, tub...@myshop.com wrote:
Quote:
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.


Guest

Fri Dec 28, 2018 1:45 pm   



On Friday, 28 December 2018 06:04:14 UTC, whit3rd wrote:
Quote:
On Thursday, December 27, 2018 at 7:12:00 PM UTC-8, tub...@myshop.com 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

Look165
Guest

Fri Dec 28, 2018 1:45 pm   



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

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

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

tubeguy_at_myshop.com a écrit le 28/12/2018 à 04:11 :
Quote:
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?


pfjw@aol.com
Guest

Fri Dec 28, 2018 2:45 pm   



http://www.circuitstoday.com/wp-content/uploads/2011/11/PiezoTransducer-Circuit-Symbol.jpg

http://www.circuitstoday.com/wp-content/uploads/2011/11/Loudspeaker-Circuit-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

Phil Allison
Guest

Sat Dec 29, 2018 5:45 am   



Look165 wrote:

Quote:

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.


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


** See above.


Quote:
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

Tim R
Guest

Fri Jan 04, 2019 3:45 pm   



On Friday, December 28, 2018 at 10:51:50 PM UTC-5, Phil Allison wrote:
Quote:
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.

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