Gainclone...No gain, YES pain. - 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 13th January 2003, 10:49 PM   #1
diyAudio Member
 
JAZZ2250's Avatar
 
Join Date: Mar 2002
Location: Seoul. Korea
Default Gainclone...No gain, YES pain.

I tried gainclone with gain=1, and it got pretty hot in a very short time. I think, according to the others' comment in this thread, it is due to an oscillation. I tried both T and TF package, and both of them got hot. Actually, I was thinking to use a gainclone as a power amp without any gain, but it doesn't seem to be possible because of the nasty oscillation.
What I'm thinking right now is that if I set the gain of gainclone to, say, 20 and put a voltage divider at the input before the coupling cap, and hook it up to a tube preamp with a maximum gain of 20 dB, would it be worth trying? As I heard, the main benifit of using tube amps is at the voltage amplification. In the configuration stated above, voltage amplification is done first at the tube stage, and signal gets lower by the voltage divider, and then voltage is amplified again by gainclone. In such a case, there wouldn't be any benifit of using a tube line stage, IMO.
I would like to know what others think about this configuration. Is it gonna be worth trying or a waste of time and money?
Thanks in advance.
  Reply With Quote
Old 13th January 2003, 11:14 PM   #2
diyAudio Member
 
Peter Daniel's Avatar
 
Join Date: Jul 2002
Location: Toronto, Canada
Send a message via AIM to Peter Daniel
Doesn't make much sense, such configuration. First you amplify, than attenuate and then amplify again.
__________________
www.audiosector.com
“Do something really well. See how much time it takes. It might be a product, a work of art, who knows? Then give it away cheaply, just because you feel that it should not cost so much, even if it took a lot of time and expensive materials to make it.” - JC
  Reply With Quote
Old 13th January 2003, 11:21 PM   #3
diyAudio Member
 
analog_sa's Avatar
 
Join Date: Aug 2002
Location: Sofia
The only way to get gain around unity from these chips is to use inverting topology.


cheers

peter
  Reply With Quote
Old 13th January 2003, 11:25 PM   #4
diyAudio Member
 
JAZZ2250's Avatar
 
Join Date: Mar 2002
Location: Seoul. Korea
Default inverting topology?

Could you explain more about it? Thanks.
  Reply With Quote
Old 14th January 2003, 01:18 AM   #5
diyAudio Member
 
JordanG's Avatar
 
Join Date: Dec 2002
Location: Atlanta, GA
Default Re: inverting topology?

Quote:
Originally posted by JAZZ2250
Could you explain more about it? Thanks.
I'd recommend reading this. It provides a nice introduction to the inverted gainclone. Also, here is a forum where people like to talk about and tweak IC based amplifiers.

hope that helps

--Jordan
  Reply With Quote
Old 14th January 2003, 01:30 AM   #6
tiroth is offline tiroth  United States
diyAudio Member
 
Join Date: Dec 2001
Location: Pittsburgh, PA, USA
Amplify, attenuate, amplify is just going to raise your noise floor.

You realize that the LM chip is not spec'd stable with gain < 10?
  Reply With Quote
Old 14th January 2003, 01:46 AM   #7
diyAudio Member
 
JAZZ2250's Avatar
 
Join Date: Mar 2002
Location: Seoul. Korea
Yes, I realized why the gain less than 10 is not recommended by NS. Definitely it doesn't seem to be a good idea to run the amp with such a low gain though I cannot hear the oscillation. It should also be applied to non-inverting configuration, right? I gotta try it.
Mmmm, then I'll have to think about which power amplifier, which is simple to build, will go well with tube preamp. Another tedious search is about to begin now. Any recommendation, please?
  Reply With Quote
Old 14th January 2003, 01:52 AM   #8
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Default Re: Gainclone...No gain, YES pain.

Hi,

Quote:

I tried gainclone with gain=1, and it got pretty hot in a very short time.
Then you did badly wrong. Big booboo. You CANNOT get unity gain in non-inverting topology, you can extremely easily get unity gain in inverting mode. Simply use a pair of 220k Resistors, one from the Amp input to the inverting input, the other from the inverting input to the Output.

NOW observe the magic. Place a 22k resistor between the inverting input and ground. Then place an 18k resistor between the positive input and ground. Unity gain and stable. Easy as pie.

Sayonara

PS, this same sort trick lets you use the OPA637 as I/V converter without osccillation. It sounds notably better than OPA627 in this position but is not unity gain stable....
  Reply With Quote
Old 14th January 2003, 02:26 AM   #9
diyAudio Member
 
JAZZ2250's Avatar
 
Join Date: Mar 2002
Location: Seoul. Korea
I used all 47k resistors. Let me see what I did wrong... I think I didn't use one resistor which is 22k in your recommendation. I directly connected the signal to a resistor which is connected to the inverting input. I thought the one (22k in yours) was not necessary because inverting input could be thought as a virtual ground. Wrong? Sorry for my poor knowledge, but I thought I had read it somewhere. Do you think putting that resistor will make a difference? Please let me know, Sayonara Sang.
  Reply With Quote
Old 14th January 2003, 07:15 AM   #10
diyAudio Member
 
analog_sa's Avatar
 
Join Date: Aug 2002
Location: Sofia
If i may volunteer a reply the 22k resistor is there to provide stable dc reference. A problem of 'textbook' inverted amps is that the offset voltage varies according to the dc resistance the inputs see relative to ground.


cheers

peter
  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
Help with GainClone gain setting johan851 Chip Amps 35 15th February 2008 06:33 PM
Inverted GainClone's gain question? 5150ed Chip Amps 15 10th July 2006 09:12 AM
The Gain in a GainClone? Mmne Chip Amps 11 26th April 2006 12:40 PM
New Gainclone with no gain: help requested SRMcGee Chip Amps 29 8th October 2004 07:31 AM


New To Site? Need Help?

All times are GMT. The time now is 05:35 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