amplifier design question - diyAudio
Go Back   Home > Forums > Amplifiers > Chip Amps

Chip Amps Amplifiers based on integrated circuits

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 21st September 2012, 03:31 PM   #1
diyAudio Member
 
Join Date: Feb 2011
Default amplifier design question

Actualy i did never design any amplifier.
Maybe played with some component values for few chipamps, but that's about it.

I seen opamps used o tame DC offset, and this led me to a question i would like to find an answer to. Do notice, I em honestly clueless if what got into my mind can be done, and even if it can be, is it a good idea or not.

Let's assume a power amplifier, something realy generic.
Is it possible to use an opamp to amplify the same input signal as the one the generic poweramp uses, compare the 2 signals, take the difference and feed it back to the generic poweramp to.. sorthof force it to make an ouput verry similar to the opamp ?
Even if it is possible, can it improve a generic poweramp?
  Reply With Quote
Old 21st September 2012, 03:36 PM   #2
diyAudio Member
 
demeterart's Avatar
 
Join Date: Jan 2012
Location: Athens, Greece
Hello Arty

what you describe indirectly thru your question is the negative feedback, the underlying control mechanism for any tamed amplifier. the op-amp would have to control the overall loop gain and thus be an integral part of the power amp design. you can not really take two completely unrelated amps and "marry" them like this without access to their internals.
  Reply With Quote
Old 21st September 2012, 03:43 PM   #3
diyAudio Member
 
Join Date: Feb 2011
okay, make the generic amp be say.. my beloved tda1557q,
and the opamp TL081 for example.
How would this have to be wired up?
And will it make a difference?
To what degree could the opamp correct the poweramp?
  Reply With Quote
Old 21st September 2012, 04:02 PM   #4
diyAudio Member
 
demeterart's Avatar
 
Join Date: Jan 2012
Location: Athens, Greece
from what i gather from web pics the tda1557 is a complete amp with no access to internals.
can not do :-(
  Reply With Quote
Old 21st September 2012, 09:24 PM   #5
johnr66 is offline johnr66  United States
diyAudio Member
 
Join Date: Mar 2009
Quote:
Originally Posted by demeterart View Post
from what i gather from web pics the tda1557 is a complete amp with no access to internals.
can not do :-(
Sounds like the OP wants global negative feedback. Take the output of the power amp and feed it back to the inverting input of the opamp through the resistor divider needed to set the proper gain. This global NF arrangement now dictates the total gain of the amplifier and corrects non linearity. If the power amp IC stage was nonlinear, the opamp would be feeding the corrective signal to its input.

I don't see why this is necessary as the power amp IC has its NF loop. The ones with fixed gain have it internal.
  Reply With Quote
Old 21st September 2012, 09:27 PM   #6
AndrewT is online now AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Maybe he should read Jung, composite opamps.
__________________
regards Andrew T.
  Reply With Quote
Old 21st September 2012, 09:51 PM   #7
diyAudio Member
 
demeterart's Avatar
 
Join Date: Jan 2012
Location: Athens, Greece
The proposed configuration by johnr66 has many potential pitfalls given the lack of access to the internal input terminals of the power amp and needed input DC bias terminals. Arty has asked for a specific forced marriage and that calls for special conditions.
  Reply With Quote
Old 21st September 2012, 11:13 PM   #8
diyAudio Member
 
Join Date: Feb 2011
it does not have to be a tda1557q ic, it was just one that popped up my mind.
say.. lm 1875 can be a target too.

has to admit i have no clue why this idea bugs me for least 30 hours now.
  Reply With Quote
Old 21st September 2012, 11:56 PM   #9
diyAudio Member
 
Join Date: Feb 2011
ah, managed a crude block diagram that more or less describes what i had in mind.


Click the image to open in full size.

surely this sketch is unable to work. but shows the basic idea behind my question.
Attached Images
File Type: jpg block2.JPG (49.8 KB, 176 views)

Last edited by Arty; 21st September 2012 at 11:58 PM.
  Reply With Quote
Old 22nd September 2012, 08:22 AM   #10
AndrewT is online now AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Have you read Jung yet?
__________________
regards Andrew T.
  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
New Amplifier design kzeprf22 Solid State 28 5th April 2009 04:45 PM
Noob amplifier design question preiter Chip Amps 2 4th August 2006 07:51 PM
Amplifier design - need help rmihai Solid State 20 12th January 2006 01:54 PM
My first amplifier design, what do you think? Fritzell Solid State 18 14th October 2005 02:12 PM


New To Site? Need Help?

All times are GMT. The time now is 05:27 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