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alzie
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Wire Recorder
alzie   9/20/2013 2:21:48 PM
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Yeah, not bad!

Now, how do we get stereo on that wire?!

 

I started out with tape recording half a century ago,

learned a whole lot.

A good place for budding engineers.

 

Although i begrudgingly use MP3 do to my distaste for compression,

at least we have gotten rid of distortion, noise, and wow n flutter.

Beats the crap out of those old cassettes!

They were compact and convenient, but

ive got most of my music collection on one 16GB player.

The plusses out weigh the minusses.

 

JGrubbs
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Re: I so want one of these!!!
JGrubbs   9/17/2013 2:03:23 PM
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Here is a link where you can download the book

Magnetic Recording Wire & Tape

http://www.tubebooks.org/Books/TapeWire.pdf

www.tubebooks.org has a lot of 1930 - 1960

technical books and data books available for

free download.

Max The Magnificent
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Re: I so want one of these!!!
Max The Magnificent   9/6/2013 2:34:16 PM
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@wbeaty: No mention of where these things came from?

Actually, I mentioned this in an earlier column in which I wrote:

The first magnetic wire recorder was created in 1899 by a Danish Engineer called Valdemar Poulsen (1869 – 1942). Commercial magnetic wire recorders for dictation and telephone recording were made almost continuously from the 1920s onwards, but the real heyday of wire recording was in the 1940s through to the mid-1950s.

wbeaty
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Re: I so want one of these!!!
wbeaty   9/6/2013 2:26:18 PM
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No mention of where these things came from?  The first I've seen wasn't a recorder, it was a radio detector: a loop of moving wire with two coils touching, antenna on the first coil and headphones on the second, and a magnet to restore the wire afterwards.  "Marconi Magnetic Detector."   Nonlinear effects presumably demodulated the RF.    I guess it was a Coherer with a single giant iron filing.

Hmm.  Was this the origin, or did wire recorders predate 1910 or so?  Firesign Theater of course insists that they were invented by native americans who recorded civil-war era theater dramas...

Max The Magnificent
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Re: try a switching amplifier to drive the record head
Max The Magnificent   8/7/2013 10:46:33 AM
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@Electrojim: ...The tradeoff is 'modulation noise,' which can be eliminated by applying a sort of 'dithering,' which puts the biased-tape noise right back.

You are making my brain hurt :-)

 

Max The Magnificent
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Re: The isle is full of noises
Max The Magnificent   8/7/2013 10:45:09 AM
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@Susan: At least she will be driving on the other side of the road. ;-)


You sweet, innocent child ... you've obviously never seen my mother drive :-)

Electrojim
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Re: try a switching amplifier to drive the record head
Electrojim   8/7/2013 10:43:10 AM
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In response to kendallcp: it works!  I did it with tape back in the early '70s, and unknown to me at the time, Joe Dundovic of Nortronics (tape heads) was experimenting with it too.  Tape goes "gracefully" into distortion when overdriven, and the only thing you have to watch out for with PWM is reaching the point when your duty cycle disappears and audio peaks slam the supply rails into the head.  This can be obviated with some form of limiter ahead of the PWM circuit, or by comparing your audio waveform with a 'peaky' clock, rather than a triangle, to generate the PWM. 

Another neat trick that works, sort-of, is to get rid of the AC bias altogether.  It's possible to predistort the audio waveform in a manner opposite to the hysteresis-loop function of the recording process, although this requires fancy phase compensation as well as the nonlinear transfer.  This gets rid of the "biased-tape noise," and really improves the high-frequency performance.  The tradeoff is 'modulation noise,' which can be eliminated by applying a sort of 'dithering,' which puts the biased-tape noise right back.  Such fun!

Susan Rambo
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Re: The isle is full of noises
Susan Rambo   8/7/2013 10:21:16 AM
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LOL. Oh, that's right. At least she will be driving on the other side of the road. ;-)

Max The Magnificent
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Re: The isle is full of noises
Max The Magnificent   8/7/2013 10:16:14 AM
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@Susan: Luckily she lives a couple states away from me...

(a) She lives in England

(b) You're still not safe :-)

Max The Magnificent
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Re: Miniature wire recorders
Max The Magnificent   8/7/2013 10:15:17 AM
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@Navelpluis: There was a brand in Austria creating extremely small types of wire recorders, called 'Miniphone'. Have a look at our website http://www.cryptomuseum.com/covert/minifon/mi51/index.htm to see one of those Miniphone recorders...

WOW Thsi is amazing (I want one!!! :-)

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