Non-Inverting GC BETTER than Invertin GC+Buffer?! - 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 22nd October 2003, 05:21 PM   #1
GregGC is offline GregGC  Canada
diyAudio Member
 
Join Date: Oct 2003
Location: Toronto
Exclamation Non-Inverting GC BETTER than Invertin GC+Buffer?!

Just registered as a member of the forum.
You guys are great. I got the bug too and I'm going to build monoblocks based on LM3875. I was deciding on the topology (Inverted vs. Non-Inverted). I did quite a bit of reading and found that people prefer the inverted topology but than (for obvious reasons) they put a buffer at the input. Some claim that that way GC sounds even better. Well the buffer is an OPAMP in a non-inverting mode with a gain of 1. If the Inverting topology has an advantage, why implement it together with the non-inverted (buffer). You might as well stick to the non-inverting GC on the first place. You'll end up with less components on the signal path, which is the reason on the first place to build the GC. Please comment. I'd appreciated.

Great forum. A lot of inspiration. Thanks!

Greg
  Reply With Quote
Old 22nd October 2003, 05:36 PM   #2
diyAudio Member
 
Join Date: Mar 2002
Fully agreed. A resistor in series with, and a cap to ground of the + input, gets rid of the funnies that can happen with the non-inverting configuration. ~ 2.2kOhm and 0.001uF
  Reply With Quote
Old 22nd October 2003, 05:58 PM   #3
GregGC is offline GregGC  Canada
diyAudio Member
 
Join Date: Oct 2003
Location: Toronto
Hi hitsware,
You are referring to a LP filter at the front of the NIGC (non-inverting GC), right?

I think KIS would be my preference. Non-inverting GC with a 100k pot at the front and an optional RC LP filter as you mentioned would be the best topology IMHO. And if i want to get rid of the NF cap have to make shure I balance the input curents of LM3857 so that it minimizes the output ofset as much as possible. Also I was thinking that one of the reason for difernt sound coud be the difference in value of the NF resistor (220k vs 20k) used in the IGC. So I'll try building NIGC with NF of 220k and 22k to gnd and 22k to gnd from the + of the 3875. It should eliminate the output ouset. At the same time with input impedance of 22k in paralel to 100k pot will turn the linear 100k pot into semi Log. I tried it and it works quite well. This way, only one input cap in the whole circuit. Hope it'll work as I think.

Greg
  Reply With Quote
Old 22nd October 2003, 06:23 PM   #4
Account Disabled
 
Join Date: Apr 2003
Location: US
Default Re: Non-Inverting GC BETTER than Invertin GC+Buffer?!

Quote:
Originally posted by GregGC
If the Inverting topology has an advantage, why implement it together with the non-inverted (buffer).
Greg

Greg: the same topic has been extensively discussed and debated in this forum. As you will find, there is no conclusive and / or emperical evidence that inventing topology sounds better.

The rumored "gains" in THD figures due to common mode rejection are in the sub-micro percentages, at best.

To give you any comfort, most SS amps use non-inverting topology. If inverting topology had that much of an advantage, you would have expected just the opposite.

Just because people believe in things doesn't mean those believes are right and fact-based.

And I am sure you will find a lot of similar things in audio in general and on this forum in particular.
  Reply With Quote
Old 22nd October 2003, 07:07 PM   #5
diyAudio Member
 
purplepeople's Avatar
 
Join Date: Mar 2003
Location: London, Ontario, Canada
I'm guessing that the buffer is used to drive the lower than normal input impedance of the IGC. Many people are using input impedance of about 10K for their IGC. The buffer could just equalize the system with the 47K impedance of many sources. What I don't understand is if they use an IGC, why not also use an inverting buffer?

:)ensen.
__________________
Those who claim to be making history are often the same ones repeating it.
  Reply With Quote
Old 22nd October 2003, 07:12 PM   #6
GregGC is offline GregGC  Canada
diyAudio Member
 
Join Date: Oct 2003
Location: Toronto
If you use opamp as a buffer it'll have the same disadvantage of relatively low input impedance as the IGC, but at least the gain of the amp will not depend on the vol control. Still more transistors on the way of the signal thogh.

Greg
  Reply With Quote
Old 22nd October 2003, 07:20 PM   #7
diyAudio Member
 
jan.didden's Avatar
 
Join Date: May 2002
Location: Great City of Turnhout, Belgium
Blog Entries: 7
Default Re: Non-Inverting GC BETTER than Invertin GC+Buffer?!

Quote:
Originally posted by GregGC
Just registered as a member of the forum.
You guys are great. I got the bug too and I'm going to build monoblocks based on LM3875. I was deciding on the topology (Inverted vs. Non-Inverted). I did quite a bit of reading and found that people prefer the inverted topology but than (for obvious reasons) they put a buffer at the input. Some claim that that way GC sounds even better. Well the buffer is an OPAMP in a non-inverting mode with a gain of 1. If the Inverting topology has an advantage, why implement it together with the non-inverted (buffer). You might as well stick to the non-inverting GC on the first place. You'll end up with less components on the signal path, which is the reason on the first place to build the GC. Please comment. I'd appreciated.

Great forum. A lot of inspiration. Thanks!

Greg
Hi Greg, welcome!

What you say is logical and puts the finger on the right spot. However, you will find out that this is not necessarily an advantage or appreciated at this forum. Still, it's a great place to learn and teach. Have fun!

Jan Didden
  Reply With Quote
Old 22nd October 2003, 07:45 PM   #8
GregGC is offline GregGC  Canada
diyAudio Member
 
Join Date: Oct 2003
Location: Toronto
Dear Jan Didden,

Thanks for the welcome.
I think that part of the learning process is questioning what we/people take for granted. I may be wrong. I'm new at this forum and I don't mind being advised on what an appropriate behavior for this forum is (mind you I red the rules when I signed-up). I thought, though that we are all open minded individuals that exchange thoughts on how to improve on a great idea. I don't get offended if I find I'm wrong in something. Also I'm not sure I'm right at assuming (read the headline). Otherwise I wouldn't have open the topic for discussion.

Life is a learning process.


Greg
  Reply With Quote
Old 22nd October 2003, 08:38 PM   #9
GregGC is offline GregGC  Canada
diyAudio Member
 
Join Date: Oct 2003
Location: Toronto
Default Re: Re: Non-Inverting GC BETTER than Invertin GC+Buffer?!

Quote:
Originally posted by millwood



Greg: the same topic has been extensively discussed and debated in this forum. As you will find, there is no conclusive and / or emperical evidence that inventing topology sounds better.

The rumored "gains" in THD figures due to common mode rejection are in the sub-micro percentages, at best.

To give you any comfort, most SS amps use non-inverting topology. If inverting topology had that much of an advantage, you would have expected just the opposite.

Just because people believe in things doesn't mean those believes are right and fact-based.

And I am sure you will find a lot of similar things in audio in general and on this forum in particular.

Thanks for your input. What do you think about my prvious message descibing the circuit I'd like to use (No NFB Cap)? I still don't know how to post pictures/diagrams.

Greg
  Reply With Quote
Old 22nd October 2003, 08:50 PM   #10
moamps is offline moamps  Croatia
diyAudio Member
 
Join Date: Oct 2002
Location: Croatia
From NS LM4780 datasheet;
Attached Images
File Type: jpg 4780.jpg (22.6 KB, 943 views)
  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
sonic differences between inverting/non-inverting LM4780 VS both non-inverting LM4780 jarthel Chip Amps 5 19th July 2007 01:37 PM
whats the difference between inverting and no inverting mikee55 Parts 1 7th January 2007 11:36 PM
Aleph Phase Inverting / non inverting macka Pass Labs 9 22nd February 2006 08:01 PM
Could a tube buffer be useful for a Non-Inverting Gainclone? Bas Horneman Chip Amps 42 3rd June 2004 09:40 PM
Bridged/Stereo, w or w/o servo, inverting 3886, inverting buffer PCB Alexander Rice Chip Amps 9 27th March 2004 07:53 PM


New To Site? Need Help?

All times are GMT. The time now is 05:07 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