Discrete Opamp Open Design - Page 209 - diyAudio
Go Back   Home > Forums > Source & Line > Analog Line Level

Analog Line Level Preamplifiers , Passive Pre-amps, Crossovers, etc.

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 14th November 2012, 09:52 AM   #2081
lineup is offline lineup  Sweden
diyAudio Member
 
lineup's Avatar
 
Join Date: Dec 2005
Location: the north
Quote:
Originally Posted by aparatusonitus View Post
I have
Discrete Opamp Open Design
Discrete Opamp Open Design

And I have another one for you
OKey, I am a bit disappointed.
Somebody else did it before me.
But I should have known... There is nothing new under the Sun.
__________________
lineup
  Reply With Quote
Old 14th November 2012, 10:14 AM   #2082
diyAudio Member
 
aparatusonitus's Avatar
 
Join Date: Jan 2004
Location: Split, Croatia
Quote:
Originally Posted by lineup View Post
OKey, I am a bit disappointed.
Don't be...I'm sure someone else have tried it even before I have.
Anyway, you can try something else and be the first one...in Rush cascode there is no limitation for active devices, you don't have to use complementary devices of the same type, e.g. you can use n-jfet/pnp, n-mfet/pnp, triode/pnp...etc
__________________
Non é mai abbastanza...
  Reply With Quote
Old 15th November 2012, 10:49 PM   #2083
diyAudio Member
 
Join Date: Nov 2011
Location: Cooktown, Oz
I've been studying Jerald Graeme's "Feedback Plots define Op Amp AC Performance", sboa015.pdf from the TI library, while playing with stability of the FET990.

There are 2 considerations for stability which also lead to 2 definitions of 'Unconditional Stability
  • Stability with different levels of NFB. This old warhorse is fairly (??!) straightforward. Easy to have a different version for gain less than 3x etc or a single NPO ceramic to change. These are my C4/5 recommendations in post #2060. Graeme helps me formalise much of my experience & thinking and introduces at least one new dodge. Prof. Cherry is excellent if you ken reed, rite & kont.
  • Stability with load. This is the important one with Power Amps as you don't often tweak NFB but you do have loadsa different loads. Output Inductors are a big help for this but for a supa dupa GP OPA, SM inductors are truly evil and muck up your 1 ppzillion THD for various reasons. But easy (?!) enough if your noise gain is fixed.
But a GP OPA might have to cope with combinations of both so the tweaks & recommended C changes can become too complicated. Zobels don't guarantee unconditional.

I think the advice in the AD797 datasheet is about the limit of complexity. The instructions for uA709 are definitely too much for washed & unwashed masses alike. Hands up those of you who have used this vintage device.

Anyone done this sort of thing recently?

Last edited by kgrlee; 15th November 2012 at 11:03 PM.
  Reply With Quote
Old 15th November 2012, 11:09 PM   #2084
fas42 is online now fas42  Australia
diyAudio Member
 
fas42's Avatar
 
Join Date: Jun 2012
Location: NSW, Australia
Blog Entries: 11
Quote:
Originally Posted by kgrlee View Post
But a GP OPA might have to cope with combinations of both so the tweaks & recommended C changes can become too complicated. Zobels don't guarantee unconditional.

I think the advice in the AD797 datasheet is about the limit of complexity. The instructions for uA709 are definitely too much for washed & unwashed masses alike. Hands up those of you who have used this vintage device.

Anyone done this sort of thing recently?
I've been interested in this stability thing for a while - the thought I would have is that since the device is discrete, what's really the point of making it general purpose, stable no matter what you throw at it? I would prefer to have a base topology, with multiple variations of the feedback and stabilising strategies, so that one could extract maximum performance depending upon what you're using it for ...

Frank
  Reply With Quote
Old 15th November 2012, 11:17 PM   #2085
diyAudio Member
 
Join Date: Nov 2011
Location: Cooktown, Oz
Quote:
Originally Posted by fas42 View Post
I would prefer to have a base topology, with multiple variations of the feedback and stabilising strategies, so that one could extract maximum performance depending upon what you're using it for ...
Frank, this is exactly what Scott & I are trying to do. The problem is that it then becomes too complicated to explain even to another guru. (not that I'm claiming guru status )

It took me a long time to be sure about my C4/5 = 15p, 47p & 100p on (mostly) resistive loads at any gain.

I'm still not happy I've got anything sensible I can explain even with polysyllables, when I add different reactive loads. (Dis be double-speak to say I'm all confused by my results )
  Reply With Quote
Old 15th November 2012, 11:32 PM   #2086
fas42 is online now fas42  Australia
diyAudio Member
 
fas42's Avatar
 
Join Date: Jun 2012
Location: NSW, Australia
Blog Entries: 11
Quote:
Originally Posted by kgrlee View Post
Frank, this is exactly what Scott & I are trying to do. The problem is that it then becomes too complicated to explain even to another guru. (not that I'm claiming guru status )
Why worry about explaining it? Have one variation that will always work, and then list the conditions that must be met to use the edgier varieties. A simple checklist, a recipe type of thing, that people can refer to: things like, at least so much closed loop gain; and, the load must be resistive, may be so much reactive, etc.

Frank
  Reply With Quote
Old 16th November 2012, 12:30 AM   #2087
diyAudio Member
 
Join Date: Mar 2002
> Hands up those of you who have used this vintage device

Hand up here. We did all compensation empirically with 10kHz squarewave.
(prescribed 2 caps and 1 resistor (no output networks))
  Reply With Quote
Old 16th November 2012, 01:49 AM   #2088
diyAudio Member
 
scott wurcer's Avatar
 
Join Date: Jan 2004
Location: cambridge ma
Quote:
Originally Posted by fas42 View Post
I've been interested in this stability thing for a while - the thought I would have is that since the device is discrete, what's really the point of making it general purpose, stable no matter what you throw at it? I would prefer to have a base topology, with multiple variations of the feedback and stabilising strategies, so that one could extract maximum performance depending upon what you're using it for ...

Frank
You got it. There several comments here and elsewhere about why bother with discrete today.

So let's list again some bona-fide reasons.

1) High voltage and current operation possibly even as an input to a 50 or 100W PA.
2) Ability to bias output for a specific load (eliminate crossover).
3) Option to custom compensate for any application (very few IC's go above G = 5 decompensation).

This weekend looks good to finish the prototype (cold and dreary). The current thought is the VAS and output on a small card with a daughter card containing the various input stages.

EDIT - I will be having a nice leg of Aussie lamb Saturday. Last week we had a 1955 Belgian bottled Charmes-Chambertin (or so it said on the label) didn't matter it had already joined the parrot.
__________________
Silence is so accurate.

Last edited by scott wurcer; 16th November 2012 at 02:04 AM.
  Reply With Quote
Old 16th November 2012, 02:20 AM   #2089
bcarso is offline bcarso  United States
diyAudio Member
 
Join Date: May 2005
Location: Canoga Park, California
Quote:
Originally Posted by scott wurcer View Post
You got it. There several comments here and elsewhere about why bother with discrete today.

So let's list again some bona-fide reasons.

1) High voltage and current operation possibly even as an input to a 50 or 100W PA.
2) Ability to bias output for a specific load (eliminate crossover).
3) Option to custom compensate for any application (very few IC's go above G = 5 decompensation).

This weekend looks good to finish the prototype (cold and dreary). The current thought is the VAS and output on a small card with a daughter card containing the various input stages.

EDIT - I will be having a nice leg of Aussie lamb Saturday. Last week we had a 1955 Belgian bottled Charmes-Chambertin (or so it said on the label) didn't matter it had already joined the parrot.
1955 Charmes-Chambertin is pushing it. Most probably bleedin' deceased. My condolences.

My oldest authentic burg is a 1983 La Tache magnum. When??
  Reply With Quote
Old 16th November 2012, 02:42 AM   #2090
fas42 is online now fas42  Australia
diyAudio Member
 
fas42's Avatar
 
Join Date: Jun 2012
Location: NSW, Australia
Blog Entries: 11
Quote:
Originally Posted by bcarso View Post
My oldest authentic burg is a 1983 La Tache magnum. When??
1983 Domaine de la Romanée-Conti La Tâche, France, Burgundy, Côte de Nuits, La Tâche Grand Cru - CellarTracker!

Frank
  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


Similar Threads
Thread Thread Starter Forum Replies Last Post
Discrete OPAMP audio-gd Vendor's Bazaar 27 20th September 2012 04:02 PM
discrete opamp help blackpowderaudio Parts 0 16th December 2009 03:46 PM
THAT transistor headphone amp (250ma discrete opamp) design sanity check. Russ White Headphone Systems 19 13th December 2007 12:52 PM


New To Site? Need Help?

All times are GMT. The time now is 01:59 PM.


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