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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!!! :-)

Max The Magnificent
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Re: Signal Corps Wire Recorder
Max The Magnificent   8/7/2013 10:12:43 AM
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@luceleaf: In the summer of 1953 I received a one month appointment as an Engineering Aid...


Hi David -- thank you for sharing this story -- I must admit I hadn't considered either of these problems (untangling the wire and the read head seeing the other side of the wire to the write head).

Having said this, I think the concept of the wire recorder is really clever and it makes a lot of sense ... all the way up to someone working out how to fabricate good magnetic tape :-)

Susan Rambo
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Re: The isle is full of noises
Susan Rambo   8/7/2013 10:11:19 AM
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Luckily she lives a couple states away from me. Thanks for the warning. 

Max The Magnificent
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Re: The isle is full of noises
Max The Magnificent   8/7/2013 10:09:29 AM
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@Susan: Put wheels on this recorder and it would be a smart car.

By some strange quirk of fate, my 83-year-old mothe rjust bought herself a Smart Car ... be afraid ... be very afraid ... :-)

Max The Magnificent
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Re: try a switching amplifier to drive the record head
Max The Magnificent   8/7/2013 10:06:19 AM
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@kendallcp: When (not if, Max!) this gets published in EET...

I am quivering in anticipation myself ... as soon as Jim finishes thsi project and writes it ut, you can bet I'll be writing about it here on EE Times!!!

Max The Magnificent
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Re: Be Prepared
Max The Magnificent   8/7/2013 10:03:50 AM
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@betajet: Batman: I like to think it's because... our hearts are pure.

LOL It was so sappy -- I loved it as a kid. I remember whenever the Riddler created a riddle and they solved it and the solutuion was so wild and wacky ("... and what eats an unripe banana at three o'clock in the afternoon Robin...") but it all seemed to make perfect sense when you were a kid... you just thought they were really clever to sort out the clues :-)

Max The Magnificent
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Re: Plated why a memory?
Max The Magnificent   8/7/2013 10:00:38 AM
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@betajet: It was usually called plated wire memory and was used by the Univac 1100 series and other computers.

It amazes me how much arcane knowledge we have between all of us... It would be such a shame to lose it all ... which leads us right back to my Are We Losing the Secrets of the Masters? column (LOL)

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