Building better High sensitivity headphones
in [Design]
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From: amdx on 22 Jul 2010 14:12 Hi Guys, I'm interested in a discussion about building a high sensitivity set of headphones. The intended use would with a crystal radio. The usual thing is to find an old set of Brandes headphones with 2000 ohms DC resistance. It seems like the collective intellect here could design or modify existing headphones to provide a better impedance match and increase the sensitivity of headphones. Maybe there are some better materials now then there were 80 years ago. Any ideas about the ideal characteristics for a set of crystal radio headphones? -- MikeK
From: Scott Dorsey on 22 Jul 2010 14:17 amdx <amdx(a)knology.net> wrote: > Hi Guys, > I'm interested in a discussion about building a high sensitivity set of >headphones. >The intended use would with a crystal radio. >The usual thing is to find an old set of Brandes headphones with 2000 ohms >DC resistance. > It seems like the collective intellect here could design or modify >existing headphones >to provide a better impedance match and increase the sensitivity of >headphones. >Maybe there are some better materials now then there were 80 years ago. > Any ideas about the ideal characteristics for a set of crystal radio >headphones? You want an infinitely high input impedance and no shunt capacitance. The old method was to use the finest possible wire, and as many turns of it as possible. This results in some design issues; because your coil is now extremely massy, you can't use a moving coil transducer design and get good high frequency response. So most of those high-Z headphones were variable reluctance types. Another old method is to use a piezoelectric transducer. I think that is still a viable method, maybe using some of the Motorola piezo horn elements. The easiest way to do it today would be to use a modern low-z headphone with a JFET follower in front of it. Gives you as high an input Z as you would ever want. But, really, that would be cheating, wouldn't it? --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis."
From: John Larkin on 22 Jul 2010 14:22 On 22 Jul 2010 14:17:41 -0400, kludge(a)panix.com (Scott Dorsey) wrote: >amdx <amdx(a)knology.net> wrote: >> Hi Guys, >> I'm interested in a discussion about building a high sensitivity set of >>headphones. >>The intended use would with a crystal radio. >>The usual thing is to find an old set of Brandes headphones with 2000 ohms >>DC resistance. >> It seems like the collective intellect here could design or modify >>existing headphones >>to provide a better impedance match and increase the sensitivity of >>headphones. >>Maybe there are some better materials now then there were 80 years ago. >> Any ideas about the ideal characteristics for a set of crystal radio >>headphones? > >You want an infinitely high input impedance and no shunt capacitance. > >The old method was to use the finest possible wire, and as many turns of >it as possible. This results in some design issues; because your coil is >now extremely massy, you can't use a moving coil transducer design and >get good high frequency response. So most of those high-Z headphones were >variable reluctance types. > >Another old method is to use a piezoelectric transducer. I think that is >still a viable method, maybe using some of the Motorola piezo horn elements. > >The easiest way to do it today would be to use a modern low-z headphone >with a JFET follower in front of it. Gives you as high an input Z as you >would ever want. But, really, that would be cheating, wouldn't it? >--scott Or use a transformer. John
From: Tim Williams on 22 Jul 2010 14:43 "John Larkin" <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote in message news:m23h46p3m6uul7vgo8n50jr4j41mitbja4(a)4ax.com... > Or use a transformer. I have a few 50kohm microphone transformers, if you're interested. IIRC, the primary is 50-300-600 ohm. Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms
From: Rich Grise on 22 Jul 2010 13:51
On Thu, 22 Jul 2010 14:17:41 -0400, Scott Dorsey wrote: > amdx <amdx(a)knology.net> wrote: >> Hi Guys, >> I'm interested in a discussion about building a high sensitivity set of >>headphones. >>The intended use would with a crystal radio. > ... > The easiest way to do it today would be to use a modern low-z headphone > with a JFET follower in front of it. Gives you as high an input Z as you > would ever want. But, really, that would be cheating, wouldn't it? Well, there's cheating and then there's cheating. If there's a powerful AM or (analog) TV station nearby, you could tune one Xtal set to that, and just derive DC from the detected RF, then power the headphone for your selected station by the DC that's generated by detecting ambient RF. Cheers! Rich |