John Curl's Blowtorch preamplifier part II - Page 3080 - diyAudio
Go Back   Home > Forums > Member Areas > The Lounge

The Lounge A place to talk about almost anything but politics and religion.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 4th December 2012, 01:34 PM   #30791
diyAudio Member
 
scott wurcer's Avatar
 
Join Date: Jan 2004
Location: cambridge ma
Quote:
Originally Posted by PMA View Post
Jan,

AD797 is difficult to keep stable. We all know it .

Cheers,
__________________
"Greetings from The Humungus! The Lord Humungus! The Warrior of the Wasteland! The Ayatollah of Rock and Rolla!" aka the Wizard of Wrestling.
  Reply With Quote
Old 4th December 2012, 01:37 PM   #30792
diyAudio Member
 
Esperado's Avatar
 
Join Date: Jul 2011
Location: France
And even here, the risk is not so important: If you share some new idea you had, people will fight endless against, just to look smart.
__________________
Ultimate Protection and more.The Only Source of Knowledge is experience, everything else is just information” ©A. Einstein
  Reply With Quote
Old 4th December 2012, 01:40 PM   #30793
diyAudio Member
 
Esperado's Avatar
 
Join Date: Jul 2011
Location: France
Quote:
Originally Posted by scott wurcer View Post
We still talk abut Jim B's visit because he couldn't believe it was designed by a "girl".
? Somebody with no brain believing girls are made the same way ?

Scott, any comment about my question: "Current feedback model with a differential input added" .
__________________
Ultimate Protection and more.The Only Source of Knowledge is experience, everything else is just information” ©A. Einstein

Last edited by Esperado; 4th December 2012 at 01:55 PM.
  Reply With Quote
Old 4th December 2012, 01:41 PM   #30794
diyAudio Member
 
john curl's Avatar
 
Join Date: Jul 2003
Location: berkeley ca
It must be stated that there is NO one 'best' op amp, of course, for audio
Each type of application may take a different type of op amp, and then you have to choose the 'best' of a category with certain necessary characteristics.
These include extra low noise, high source impedance drive (like an input pot), low input current, high current drive, extra fast, extra trimmed, mini-dip, single, dual, or quad, etc.
So, if for example, note the AD825. People will say: fast, known to sound 'good', fet input, reasonable output current driver.
Critics will say: Too expensive, too noisy, won't drive headphones without extra current drive, etc.
Of course, both people are 'right', but for a LINE AMP, the AD825 fits pretty well.
However, for a phono preamp, it is a lousy choice, BECAUSE it is too darn noisy.
Then, we look toward the AD797, a similar topology, but very quiet bipolar input, or something similar from another vendor. 1nV/rt Hz is necessary for phono input.
Now, what about instrumentation?
Here is where that AD797 excels! With Scott's patented extra connection, the audio frequency distortion can drop to virtually zero levels, for all practical purposes. AND that is what I have been using in the 'front end' of my ST1700B for the last 15 years, after either Scott or Walt sent me some.
However, for a second stage and working input impedances over 1Kohm, the AD797 is not the optimum device. Then a jfet input op amp is usually better. That is why I often use an OPA 134. It is reasonably quiet, has reasonably low input offset, comes in mini-dip, reasonably fast, reasonably low distortion, reasonably good drive current, reasonably high power supply voltages, etc., and reasonably inexpensive.
Kind of like a Honda. Not the best at anything, but pretty good, all around.
So where does discrete design come in, in today's audio electronics?
Well, like a super car takes a super engine, etc, so 'super' audio electronics takes discrete devices to achieve yet another level of performance.
It might not be: static distortion, but it might be: more output swing, lower input noise (0.3-0.4 nV/rt Hz is easily possible) or true balanced input to output , more output current, or that illusive thing called 'extra good sounding', that is so controversial, even here on this thread.
This is why I generally use discrete designs for my 'best' efforts, even today.
  Reply With Quote
Old 4th December 2012, 01:48 PM   #30795
diyAudio Member
 
john curl's Avatar
 
Join Date: Jul 2003
Location: berkeley ca
Jim B. is a very smart guy. He is just 'prejudiced' against women. It comes from his early background and his emulating a sort of a Sicilian 'gangster'. He has gotten into far worse trouble over women than some casual comment about the lady designer at AD. By the way, she is really smart too. I wish I knew her better, but we only met once, and do not cross the same paths. How is she, Scott? Say hello for me, although she might not remember meeting me at one of the AD conferences, perhaps 10 years ago.

Last edited by john curl; 4th December 2012 at 01:55 PM.
  Reply With Quote
Old 4th December 2012, 01:56 PM   #30796
Bonsai is offline Bonsai  Taiwan
diyAudio Member
 
Bonsai's Avatar
 
Join Date: Jul 2003
Location: Taipei, Taiwan
Quote:
Originally Posted by PMA View Post
Really? Where did you get it. 150nA.
150nA is high - that's one of the draw backs of the 5532/34 (200nA typical).

You cannot direct couple to a volume control put because you get scratching sounds as you rotate the pot.

JFET opamps are great for this, but the LM4562 is also good at 10nA (typ) although input bias does rise with input common mode voltage.

A switched attenuator is the solution for high input bias opamps - yo cn then direct couple but the problem is they are expensive.
__________________
bonsai
Amplifier Design and Construction for MUSIC! http://hifisonix.com/
  Reply With Quote
Old 4th December 2012, 02:13 PM   #30797
PMA is offline PMA  Europe
diyAudio Member
 
PMA's Avatar
 
Join Date: Apr 2002
Location: Prague
To me "high" was input bias current of AD829 "family" - 3uA.

150nA I consider as "standard" for BJT opamps where no special circuit design is made to reduce input bias current.
__________________
Pavel Macura
http://web.telecom.cz/macura/audiopage.html
  Reply With Quote
Old 4th December 2012, 02:20 PM   #30798
diyAudio Member
 
Esperado's Avatar
 
Join Date: Jul 2011
Location: France
Quote:
Originally Posted by john curl View Post
Jim B. is a very smart guy.
I don't know him, John, it was just a joke about equal rights: "Somebody with no brain believing girls are made the same way".

About choosing an OPamp, it is always a hard work. We always need half of this one, half of that one :-)
And when we have one favorite, it is immediately out of production.
__________________
Ultimate Protection and more.The Only Source of Knowledge is experience, everything else is just information” ©A. Einstein

Last edited by Esperado; 4th December 2012 at 02:24 PM.
  Reply With Quote
Old 4th December 2012, 02:38 PM   #30799
jcx is offline jcx  United States
diyAudio Member
 
Join Date: Feb 2003
Location: ..
"precision CFA" wasn't immediately popular - the AD846 didn't last long - presumably no one bought it
I only used it in a few circuits in a R&D effort/prototype that didn't become a product

there are "CFA derived" VFA that put a (~ diamond) buffer in front of the (now fixed, internal) rx and the -in LM6171 is one example
  Reply With Quote
Old 4th December 2012, 02:46 PM   #30800
PMA is offline PMA  Europe
diyAudio Member
 
PMA's Avatar
 
Join Date: Apr 2002
Location: Prague
Quote:
Originally Posted by jneutron View Post


Squirrel cage? Is this what you mean?


jn
Attached is the photo of the 63kA (for up to 20 periods of 50Hz shrt circt current) shunt with which the 3554 amp was used. Top photo is a squirrel cage, this was inside coaxial cylindrical return. BW: 0 - 2MHz.

Cheers,
Attached Images
File Type: jpg shunt63kA.jpg (143.5 KB, 134 views)
__________________
Pavel Macura
http://web.telecom.cz/macura/audiopage.html
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



New To Site? Need Help?

All times are GMT. The time now is 10:53 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright ©1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2