Discrete Opamp Open Design - Page 61 - 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 1st September 2012, 12:01 AM   #601
bcarso is offline bcarso  United States
diyAudio Member
 
Join Date: May 2005
Location: Canoga Park, California
Quote:
Originally Posted by scott wurcer View Post
JFET's have two temperature coefficients the Idss and the Vp are opposite in sign so there is a point of zero TC.
Thanks Scott. Yes, precisely. I suppose I wouldn't violate the fair use doctrine too much to copy the entire short section of Cobbold, as I believe it is long out of print.
  Reply With Quote
Old 1st September 2012, 12:05 AM   #602
diyAudio Member
 
scott wurcer's Avatar
 
Join Date: Jan 2004
Location: cambridge ma
Quote:
Originally Posted by bcarso View Post
Thanks Scott. Yes, precisely. I suppose I wouldn't violate the fair use doctrine too much to copy the entire short section of Cobbold, as I believe it is long out of print.
My copy walked years ago, Abebooks has it off and on for $70 or so.
__________________
"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 1st September 2012, 12:44 AM   #603
bcarso is offline bcarso  United States
diyAudio Member
 
Join Date: May 2005
Location: Canoga Park, California
Quote:
Originally Posted by scott wurcer View Post
My copy walked years ago, Abebooks has it off and on for $70 or so.
I just checked. Yes, OOP for sure. However:

BookFinder.com: Search for New & Used Books, Textbooks, Out-of-Print and Rare Books, which searches most of the sites (sometimes misses recent Amazon offerings though), has some a lot cheaper, probably ex-library even when they don't say that explicitly. That's my go-to for comparables on books, particularly when I find I have duplicate copies.

I love to look at the front free endpaper on books of that age, when I still used to write my name there. You can actually make out the spelling, easily. Not anymore
  Reply With Quote
Old 1st September 2012, 06:32 PM   #604
RNMarsh is offline 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
As good a reason as any.
They also allowed for as few transistors as possible (no need for additional current sources for bjt biasing). It works very well --- if you find the matches as suggested; I got about 15-20% matches (.8v/1K) out of a batch of the jFETs.
  Reply With Quote
Old 1st September 2012, 06:40 PM   #605
RNMarsh is offline RNMarsh  United States
diyAudio Member
 
RNMarsh's Avatar
 
Join Date: May 2012
Location: 2457 Cascade Trail; Cool, CA. 95614
Default close enough?

Quote:
Originally Posted by scott wurcer View Post
Sorry Dick I misread the schematic (I read 51.1 Ohms on the penciled in values), you were aiming at 800uA but does not look too close.
.8v is about it but what I get from the circuit works extreamly well.... maybe could be even better... but was not needed. Maybe the data spec sheet is a little different from the devices I have... who knows. I didnt pursue it further when the prototype was as stable as it is. Thx-RNM

Last edited by RNMarsh; 1st September 2012 at 07:06 PM.
  Reply With Quote
Old 1st September 2012, 07:59 PM   #606
diyAudio Member
 
scott wurcer's Avatar
 
Join Date: Jan 2004
Location: cambridge ma
Quote:
Originally Posted by RNMarsh View Post
.8v is about it but what I get from the circuit works extreamly well.... maybe could be even better... but was not needed. Maybe the data spec sheet is a little different from the devices I have... who knows. I didnt pursue it further when the prototype was as stable as it is. Thx-RNM

Right, nothing gained by belaboring these details.
__________________
"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 1st September 2012, 07:59 PM   #607
RNMarsh is offline RNMarsh  United States
diyAudio Member
 
RNMarsh's Avatar
 
Join Date: May 2012
Location: 2457 Cascade Trail; Cool, CA. 95614
Quote:
Originally Posted by RNMarsh View Post
.8v is about it but what I get from the circuit works extreamly well.... maybe could be even better... but was not needed. Maybe the data spec sheet is a little different from the devices I have... who knows. I didnt pursue it further when the prototype was as stable as it is. Thx-RNM
An added final clarification: Note also that even though the matching uses .8 mA. With the values used in circuit (Re = 650 instead of 1K), the actual Id measures 1.1-1.2mA. Which is right where it needs to be for low TC.
-RNM

Last edited by RNMarsh; 1st September 2012 at 08:14 PM.
  Reply With Quote
Old 1st September 2012, 08:12 PM   #608
diyAudio Member
 
scott wurcer's Avatar
 
Join Date: Jan 2004
Location: cambridge ma
Quote:
Originally Posted by bcarso View Post
I just checked. Yes, OOP for sure. However:

BookFinder.com: Search for New & Used Books, Textbooks, Out-of-Print and Rare Books, which searches most of the sites (sometimes misses recent Amazon offerings though), has some a lot cheaper, probably ex-library even when they don't say that explicitly. That's my go-to for comparables on books, particularly when I find I have duplicate copies.

I love to look at the front free endpaper on books of that age, when I still used to write my name there. You can actually make out the spelling, easily. Not anymore

Ironic that this returned Abebooks as the lowest available ~$11, in any case certainly worth replacement at that price.
__________________
"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 1st September 2012, 08:18 PM   #609
diyAudio Member
 
scott wurcer's Avatar
 
Join Date: Jan 2004
Location: cambridge ma
Quote:
Originally Posted by RNMarsh View Post
An added final clarification: Note also that even though the matching uses .8 mA. With the values used in circuit (Re = 650 instead of 1K), the actual Id measures 1.1-1.2mA. Which is right where it needs to be for low TC.
-RNM
Dick. you could use an avatar and nice pithy signature.
__________________
"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 1st September 2012, 08:29 PM   #610
bcarso is offline bcarso  United States
diyAudio Member
 
Join Date: May 2005
Location: Canoga Park, California
Quote:
Originally Posted by scott wurcer View Post
Ironic that this returned Abebooks as the lowest available ~$11, in any case certainly worth replacement at that price.
Yes, despite the improvements in parts since 1970, it holds up well.
  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 09:42 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