Discrete Opamp Open Design - Page 65 - 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 3rd September 2012, 07:57 PM   #641
diyAudio Member
 
scott wurcer's Avatar
 
Join Date: Jan 2004
Location: cambridge ma
Quote:
Originally Posted by RNMarsh View Post
PS - On the mid-level of gnfb circuit without dc servo... some have wondered just how stable over the long term it could be. After a year of service, I measured the dc offset at the output again and it is exactly where i left it a year ago..... .00x + or - a couple mV. -RNM

Gee, I thought you meant temperature stability we usually go 0 to 70C min. Even my Hafler DH220 was only a few mV off after a year with a pot across two diodes for trim (at room temp).

I don't really relate to these standards of performance, if you have some need to flog your circuit go for it.
__________________
"The question of who is right and who is wrong has seemed to me always too small to be worth a moment's thought, while the question of what is right and what is wrong has seemed all-important."
  Reply With Quote
Old 3rd September 2012, 08:18 PM   #642
RNMarsh is online now RNMarsh  United States
diyAudio Member
 
RNMarsh's Avatar
 
Join Date: May 2012
Location: 2457 Cascade Trail; Cool, CA. 95614
Default Enough about you -

Quote:
Originally Posted by scott wurcer View Post
I don't really relate to these standards of performance, if you have some need to flog your circuit go for it.
Not really. Comments trigger thought and so i write them down. I dont sell any IC's or have any stake in IC or opamps or any other topology. btw - I have already commented on its temp stability range as well..... there hasnt been shown any change in the short term and now shown in the long term drift, either.

Or, do you mean --- Enough About You. Let's talk About Me. ?

:-)

Last edited by RNMarsh; 3rd September 2012 at 08:33 PM.
  Reply With Quote
Old 3rd September 2012, 08:38 PM   #643
diyAudio Member
 
Wavebourn's Avatar
 
Join Date: Sep 2006
Location: Pleasant Hill, CA
Send a message via Skype™ to Wavebourn
Quote:
Originally Posted by coluke View Post
Never say never - current-mode open-loop topologies are indeed capable of very low THD: I've built and tested a HP amplifier based on a pretty standard architecture (diamond in - transimpedance gain stage - high current diamond out) whose THD is in the -100 dB range (low order only) @ 1 kHz, 0 dBV into 30 ohm. And it sounds very good, too , but it is by far too much complex to be mentioned here (about 20 BJTs - basically a discrete CFA). You can easily convert it to closed-loop, and that's the reason why I gave a try to this architecture.

I think the Ayre KX-R is based on the same concept.

L.
How can you claim no feedback when you used Diamond buffers with 100% negative feedbacks?

Being a student I got a bottle of cognac by making an amp on emitter followers only, with auto-transformer in the middle. 100% feedback, unity-gain stages.
__________________
The Devil is not so terrible as his math model is!
  Reply With Quote
Old 3rd September 2012, 08:43 PM   #644
RNMarsh is online now RNMarsh  United States
diyAudio Member
 
RNMarsh's Avatar
 
Join Date: May 2012
Location: 2457 Cascade Trail; Cool, CA. 95614
Quote:
Originally Posted by scott wurcer View Post
. Even my Hafler DH220 was only a few mV off after a year with a pot across two diodes for trim (at room temp).
[The Hafler DH220 is cap coupled in the feedback via 470mfd bipolar. It also isnt jFET on the input; Much easier to be dc stable with bipolar]
  Reply With Quote
Old 3rd September 2012, 09:04 PM   #645
coluke is offline coluke  Italy
diyAudio Member
 
Join Date: Mar 2009
Quote:
Originally Posted by Wavebourn View Post
How can you claim no feedback when you used Diamond buffers with 100% negative feedbacks?

Being a student I got a bottle of cognac by making an amp on emitter followers only, with auto-transformer in the middle. 100% feedback, unity-gain stages.


I meant no * global * feedback. But tons of local feedback, of course; and Sziklai pairs in the output diamond, too - actually I have nothing against Harold Black, but the performances of the CF architecture I did mention (which is more or less the standard one - you can see it in an awful lot of monolithic CFAs) are quite amazing.

L.
  Reply With Quote
Old 3rd September 2012, 09:26 PM   #646
RNMarsh is online now RNMarsh  United States
diyAudio Member
 
RNMarsh's Avatar
 
Join Date: May 2012
Location: 2457 Cascade Trail; Cool, CA. 95614
Default CFA

Quote:
Originally Posted by coluke View Post


I meant no * global * feedback. But tons of local feedback, of course; and Sziklai pairs in the output diamond, too - actually I have nothing against Harold Black, but the performances of the CF architecture I did mention (which is more or less the standard one - you can see it in an awful lot of monolithic CFAs) are quite amazing.

L.
Can you give examples of good discrete CFA designs/schematics with the output stage similar to your idea?

Last edited by RNMarsh; 3rd September 2012 at 09:30 PM.
  Reply With Quote
Old 3rd September 2012, 09:33 PM   #647
diyAudio Member
 
scott wurcer's Avatar
 
Join Date: Jan 2004
Location: cambridge ma
Quote:
Originally Posted by RNMarsh View Post
Not really. Comments trigger thought and so i write them down. I dont sell any IC's or have any stake in IC or opamps or any other topology. btw - I have already commented on its temp stability range as well..... there hasnt been shown any change in the short term and now shown in the long term drift, either.

Or, do you mean --- Enough About You. Let's talk About Me. ?

:-)
Folks here know me well enough I have nothing to sell and could care less what you think of me. The truth is you do have something to sell unless your web site is just for show.
__________________
"The question of who is right and who is wrong has seemed to me always too small to be worth a moment's thought, while the question of what is right and what is wrong has seemed all-important."
  Reply With Quote
Old 3rd September 2012, 09:48 PM   #648
BrianL is offline BrianL  United States
diyAudio Member
 
Join Date: Mar 2002
Location: USA
Scott,

Don't you mean "couldn't care less"... ;-)
__________________
bel
  Reply With Quote
Old 3rd September 2012, 09:51 PM   #649
diyAudio Member
 
scott wurcer's Avatar
 
Join Date: Jan 2004
Location: cambridge ma
Quote:
Originally Posted by BrianL View Post
Scott,

Don't you mean "couldn't care less"... ;-)
I guess, God is in the details.
__________________
"The question of who is right and who is wrong has seemed to me always too small to be worth a moment's thought, while the question of what is right and what is wrong has seemed all-important."
  Reply With Quote
Old 3rd September 2012, 09:56 PM   #650
diyAudio Member
 
Wavebourn's Avatar
 
Join Date: Sep 2006
Location: Pleasant Hill, CA
Send a message via Skype™ to Wavebourn
Quote:
Originally Posted by RNMarsh View Post
Can you give examples of good discrete CFA designs/schematics with the output stage similar to your idea?

Here you go, from this thread several pages ago:

Quote:
Originally Posted by Wavebourn View Post
Here is one more topology that can be used in custom discrete opamp as an output stage. Actually, it is complementary symmetric opamp with 100% feedback. As drawn, it works in class AB, but output devices do not go through cut-off. If to remove diode-resistor shortening networks in tails and decrease values of resistors in tails it works in class A.
Diodes in current mirrors can be replaced by transistors. But not diodes in right sides of diffpairs: transistors have low base-emitter breakdown voltage, and when the amp goes from voltage follower mode to current amplifier mode (shortened output, or too low load impedance) transistors would be fried.
Resistors in tails instead of current sources are there on purpose: max current depends on output signal level.

Click the image to open in full size.
For line level current mirrors better to be more balanced: R5 and R6 decreased, R9 and R10 increased. And transistors in places of D1 and D6.
__________________
The Devil is not so terrible as his math model is!

Last edited by Wavebourn; 3rd September 2012 at 10:00 PM.
  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 05:02 PM
discrete opamp help blackpowderaudio Parts 0 16th December 2009 04:46 PM
THAT transistor headphone amp (250ma discrete opamp) design sanity check. Russ White Headphone Systems 19 13th December 2007 01:52 PM


New To Site? Need Help?

All times are GMT. The time now is 08:32 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