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Old 2nd November 2005, 06:54 AM   #1
Electrons are yellow and more is better!
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Default I'm wondering about AD745

Somebody I know like the AD745, ultra low noise JFET input opamp from Analog Devices.

Q1: Why only SOIC16 wide as the only package? Any clue? Before they had SOIC08 and DIIL08. I'll guess this has to do with market since it's rather old (1990).

Q2: Is this the best JFET opamp in the world in noise perspective?

Q3: Anybody why used this opamp lately besides Sigurd?

http://coset.se/tmp/Audio/Hagerman/O...ptersNo011.jpg
http://www.audiocircle.com/circles/v...ic.php?t=21339
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Old 2nd November 2005, 03:07 PM   #2
jcx is offline jcx  United States
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die size? - the input fets alone take up more area than many complete op amps (i have old data book, die drawings have been removed from newer data sheets)

large area gives low channel R and low noise, fab process is also very important for 1/f noise corner

the low noise/large area input fet comes at a cost - large input C and distortion from fet parasitic C modulation with Vcm, balance +/- input Z, keep it low to minimize input distortion - or just use in inverting amps to avoid cm modulation
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Old 2nd November 2005, 03:40 PM   #3
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When I read the datasheet once again I'll see that there has never been a SOIC08, just holemounted versionen so die size seems to be a reasonable explantion.
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Old 2nd November 2005, 04:19 PM   #4
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P-A, this is an excelent circuit, but as I know, is out of program... The same service make for you dif. stage with two 2SK170 ( or eq. ) + some good opamp...
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Old 3rd November 2005, 04:44 AM   #5
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Out of program? AD sells it.
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Old 3rd November 2005, 02:43 PM   #6
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The AD745 is not out of program. I just ordered some

I am not the only person who likes the AD745 a lot. Walt J is using it in his new book "OPamp Applications" on page 6.22 and 6.24.
Gary Galo is using it in his article about the Adcomp upgrade in audioXpress 2/04,
and he is also using it in his "Music Library Preamp" in audioXpress 3/05.
And of course I am using it in my Hagerman Superbugle
But I do not have an adapter for it

The AD745 has extremely low voltage noise at 2.9nV/srqt(Hz) and 6.9fA/sqrt(Hz) current noise,
and 0.0002% dist. 100uV typical DC offset (K-grade).
One of its main advantages is that it is made for higher gains and thus fits like a glove for RIAA amplifiers

Input C is about 18pF.

Sigurd
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Old 11th April 2006, 11:11 AM   #7
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Has anyone used this opamp for any demanding task, besides Mr. Ruschkowski?

http://www.diyaudio.com/forums/showt...381#post843381

As noted Mr. Walt Jung recommends it in a phono amp design.
Page 6.24

As an accident I found AD4004 . Anyone tested it?
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