Opamp with x10 gain and bootstrapped supply rails. - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

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 28th March 2003, 05:04 AM   #1
diyAudio Member
 
Circlotron's Avatar
 
Join Date: Jun 2002
Location: Melbourne, Australia
Default Opamp with x10 gain and bootstrapped supply rails.

This is a difficult thing to get my head around.
Imagine an opamp with it's zero volt power rail referenced to the speaker output connection of a unity gain power amp it is feeding. If we make the opamp a x1 buffer it works fine and it's output swing is not limited by it's supply rails because they move up and down together with the output signal. What I want to do though is to make this opamp stage have a x10 gain. This is a bit more tricky than it first appears. Can anybody help me here?
__________________
Best-ever T/S parameter spreadsheet.
http://www.diyaudio.com/forums/multi...tml#post353269
  Reply With Quote
Old 28th March 2003, 04:02 PM   #2
jcarr is offline jcarr  United States
diyAudio Member
 
Join Date: Jul 2002
Location: Tokyo, Japan
Graham: Assuming that I understand your question correctly , bootstrapped cascoding is usually accomplished through one of two process, and depending on the particular process, can be considered as a form of either feedforward or feedback.

For feedforward operation, the reference for the bootstrapped cascode is derived from the same signal used to drive the circuit being cascoded. In other words, you take the input signal, level-shift it, and feed it to the cascode. This method works best when the gain is 1 - otherwise you will need an additional gain circuit to make sure that the cascode accurately tracks the circuit being cascoded.

For feedback operation, the reference for the bootstrapped cascode is derived from the output signal of the circuit being cascoded. Since it is merely following the output signal and level-shifting it, the bootstrapped cascode can remain blissfully oblivious of whatever gain factor is used for the circuit being cascoded.

I use both methods regularly in my own circuits, and can confirm that they are great tools in practice - both dependable and invaluable.

Please let me know if this is what you wanted to know, as my answer is admittedly absurdly simple. Recalling some of the circuits that you have cooked up in the past , I fear that you may have had something much more complex and sophisticated in mind when you initiated this thread.

regards, jonathan carr
__________________
http://www.lyraconnoisseur.com/, http://www.lyraaudio.com
  Reply With Quote
Old 28th March 2003, 05:48 PM   #3
diyAudio Member
 
Join Date: Jul 2002
Location: South Africa
Hi,
did You see TNT HDOA on www.tnt-audio.com? Maybe that's what You're looking for...
Keep well.
Jack
  Reply With Quote
Old 28th March 2003, 05:55 PM   #4
Won is offline Won
diyAudio Member
 
Join Date: Nov 2001
Location: Cambridge, Mass
I was thinking that cascoding a JFET buffer (probably use it in a line amp or head amp) would actually approach the "absurdly simple" implementation. Since JFETs are depletion mode, their source is at a higher potential than the base (for N JFETS) so JFET cascodes can self bias.

I was thinking about the feedback/feedforward differences. They are more similar than not, but the feedback method looks like a cascode and the feedforward method looks like a tracking regulated power supply. Just an interesting observation.

-Won
  Reply With Quote
Old 29th March 2003, 07:33 AM   #5
djk is offline djk
diyAudio Member
 
djk's Avatar
 
Join Date: Feb 2001
Location: USA
Do a search at Linear Technology and Analog Devices on 'suspended supply' operation. The gain calcs are complicated and resistors will have to be selected to better than 1%

To me it makes more sense to use the Hafler 'Trans Nova' operation. The opamp supplies are referenced to ground and outputs drive ground. The center tap on the transformer becomes 'hot'.

QSC, Crown, Hafler, etc, all use this circuit.
  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
ESP P3A with higher supply rails Flavio88 Solid State 20 29th September 2007 10:49 AM
Gain / supply rails query Khron Chip Amps 3 10th June 2006 10:47 AM
Single supply opamp - unequal rail voltage and opamp selection Hans L Parts 8 19th February 2006 02:15 PM
Lower supply rails for this amp? mik Solid State 4 11th June 2003 10:22 AM


New To Site? Need Help?

All times are GMT. The time now is 11:16 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