I'm wondering about AD745

peranders · 2nd November 2005, 06:54 AM

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

jcx · 2nd November 2005, 03:07 PM

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

peranders · 2nd November 2005, 03:40 PM

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.

Upupa Epops · 2nd November 2005, 04:19 PM

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...

peranders · 3rd November 2005, 04:44 AM

Out of program? AD sells it.

Sigurd Ruschkow · 3rd November 2005, 02:43 PM

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

peranders · 11th April 2006, 11:11 AM

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?

2nd November 2005, 06:54 AM	#1
peranders Electrons are yellow and more is better! diyAudio Member Join Date: Apr 2002 Location: Göteborg, Sweden Blog Entries: 4	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 __________________ /Per-Anders (my first name) or P-A as my friends call me

2nd November 2005, 03:40 PM	#3
peranders Electrons are yellow and more is better! diyAudio Member Join Date: Apr 2002 Location: Göteborg, Sweden Blog Entries: 4	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. __________________ /Per-Anders (my first name) or P-A as my friends call me

3rd November 2005, 04:44 AM	#5
peranders Electrons are yellow and more is better! diyAudio Member Join Date: Apr 2002 Location: Göteborg, Sweden Blog Entries: 4	Out of program? AD sells it. __________________ /Per-Anders (my first name) or P-A as my friends call me

11th April 2006, 11:11 AM	#7
peranders Electrons are yellow and more is better! diyAudio Member Join Date: Apr 2002 Location: Göteborg, Sweden Blog Entries: 4	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? __________________ /Per-Anders (my first name) or P-A as my friends call me

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2nd November 2005, 03:07 PM	#2
jcx diyAudio Member Join Date: Feb 2003 Location: ..	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

2nd November 2005, 04:19 PM	#4
Upupa Epops diyAudio Member Join Date: Aug 2003 Location: Prague,Czech Republic	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...

3rd November 2005, 02:43 PM	#6
Sigurd Ruschkow diyAudio Member Join Date: Oct 2004	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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