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Old 25th July 2011, 08:03 PM   #14321
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Originally Posted by PMA View Post
Completely agreed. And sometimes it is horrible.
And sometimes you really need the isolation. I did an American Football Stadium. The control room is high on the 50 yd line the amplifiers are ground level outside the end zone (1/4 turn around and all the up and down you want). To get the S/N to where you could not here noise at the field level 50 m-ish I had to use transformers on the send and receive ends! (Electronic balanced was tried and did not work even with a single transformer.) Yes it was 2 conductor shielded wire between the 2. Actually 6 pair cable, but I don't think there was an overall shield. It was foil not woven shield.

But that is not exactly high end high fidelity gear.
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Old 25th July 2011, 08:07 PM   #14322
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I am not saying one does not need an isolation. In fact any signal should be isolated. It is nice when we can convert them to something than can be transferred through optical fibre. This is the only ISOLATION.
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Old 25th July 2011, 08:10 PM   #14323
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Hi Simon,

Glanced over your schematic and my eye got caught by U5. I might be missing something, but should inverting input of U5 not be also connected to ground through resistor, like R16 in the case of U6?

Vac
Not required. R3, R6, R9, R12 through C2 provide the load to R14/C25. At the 1000 hz operating frequency it is about 700 ohms.

R16 probably could go away!
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Old 25th July 2011, 08:12 PM   #14324
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OR R16 could be removed to reduce noise and lower distortion? '-)
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Old 25th July 2011, 08:14 PM   #14325
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I am not saying one does not need an isolation. In fact any signal should be isolated. It is nice when we can convert them to something than can be transferred through optical fibre. This is the only ISOLATION.
Pavel,

I tuned up another NFL American Football Stadium. Even outdoors the digital signal processor and fiber optic transfer system did not sound very good. Until "Pro" audio links improve I will stick with analog!

Last year's arena, I was heading up to the amplifier room with a portable CD player to test some stuff. One of the college kids looked at my CD player and commented "Wow... Retro." I don't think I am ready to check out a system with MP3's yet!
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Old 25th July 2011, 08:16 PM   #14326
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Originally Posted by simon7000 View Post
Not required. R3, R6, R9, R12 through C2 provide the load to R14/C25. At the 1000 hz operating frequency it is about 700 ohms.

R16 probably could go away!
Yes, was too fast posting, after looking at it againt it is more the other way around. No reason to have high pass filter with including phase shift at this location.
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Old 25th July 2011, 10:28 PM   #14327
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Originally Posted by janneman View Post
Good paper Scott, thanks.

What struck me is the style of drawing the opamp symbol as well as the general drawing style. It reminds me of the books, articles and app notes by Gerald Graeme, one of the last analog guru's of Burr-Brown. Was there a connection between ADI and him?

jan didden
They both harken back to George Philbrick AFAIK, I wish some of their analog computing books were available on line.
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Old 25th July 2011, 11:19 PM   #14328
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Originally Posted by scott wurcer View Post
A picture is still worth a few posts. The problem has been dealt with in printing images for years. The difference with and without something like error diffusion dithering in a quantized image is pretty obvious.

http://www.cs.princeton.edu/courses/...her/dither.pdf
That's excellent Scott.
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Old 26th July 2011, 12:56 AM   #14329
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They both harken back to George Philbrick AFAIK, I wish some of their analog computing books were available on line.
Well thanks to guys like Bob Pease and Jim Williams there is a record of much of this early literature. Put aside the acrimony for a few hours and check this timeless stuff out.

The Philbrick Archive
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Old 26th July 2011, 01:11 AM   #14330
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Scott,

Thanks for this great link, I will have hours of pleasure reading it.

Great illustration on the front page. Just wait till the tube guys find out an opamp may look like something like this.
Click the image to open in full size.
They will go nuts and have their time machines spinning before you know it.

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