My_Ref Fremen Edition - Collaborative DC-Servo design - Page 13 - 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 17th June 2014, 10:36 PM   #121
diyAudio Member
 
Join Date: Feb 2013
Location: Netherlands
LM3886 My_refservo14.png

Simulation of the above schematic. Close to zero audio signal at the servo input. It takes 90 seconds to reach zero offset. Could this be correct?
__________________
Regards Mark.
  Reply With Quote
Old 17th June 2014, 10:55 PM   #122
Reality first!
diyAudio Member
 
ClaveFremen's Avatar
 
Join Date: May 2005
Location: Milan, Italy
Wow, Mark.. it seem to work too good to be true...
__________________
Dario
ClaveFremen "Bailando Salsa en el Sietch"
  Reply With Quote
Old 20th June 2014, 05:15 AM   #123
diyAudio Member
 
Join Date: Feb 2008
Location: Jackson,michigan
I just found a circuit that you may find of interest on page 10 of this document,

http://www.ti.com/lit/ds/symlink/lme49610.pdf

It is basically the same concept only it is using a LME49610 as an output buffer for only +/-250ma.

FWIW

jer
  Reply With Quote
Old 9th August 2014, 08:20 PM   #124
UnixMan is offline UnixMan  Europe
diyAudio Member
 
UnixMan's Avatar
 
Join Date: Apr 2005
Location: Perugia + L'Aquila, Italy
Send a message via ICQ to UnixMan
Quote:
Originally Posted by spinwell View Post
Hello,

one crazy idea: is there any experience of using of a capacitance multiplier in the audio signal path? It could be used instead of the branch C9-R10.
it is equivalent to the cap, thus not as much effective as a servo could be, but it's definitely a quite interesting idea!

Of course it's impossible to say in advance whether it would be better or worse than just a plain cap, especially sound wise.

A similar approach could be to remove C9 and use a gyrator (a virtual inductor, of large value) in parallel with the global feedback resistor (same effect: bringing down to unity the gain at DC).

Could be worth trying both.
__________________
Quote:
"We should no more let numbers define audio quality than we would let chemical analysis be the arbiter of fine wines." N.P.

Last edited by UnixMan; 9th August 2014 at 08:22 PM.
  Reply With Quote
Old 9th August 2014, 08:37 PM   #125
UnixMan is offline UnixMan  Europe
diyAudio Member
 
UnixMan's Avatar
 
Join Date: Apr 2005
Location: Perugia + L'Aquila, Italy
Send a message via ICQ to UnixMan
Back to the servo, the more I think about it the more I believe that the best place to inject the integrator output is between the 318 and the 3886, on one of the two inputs of the Howland Current Pump.

That would require much more (DC) gain by the integrator, but OTOH it would avoid interfering with the input differential.

Moreover, being in the middle of the overall NFB loop, any spurious signal (noise, etc) added by the servo will be drastically reduced by the NFB.

Though I wonder why Mauro have chosen a more conventional approach, acting on the input, for his own "Evolution" design...
__________________
Quote:
"We should no more let numbers define audio quality than we would let chemical analysis be the arbiter of fine wines." N.P.

Last edited by UnixMan; 9th August 2014 at 08:39 PM.
  Reply With Quote
Old 10th August 2014, 07:52 AM   #126
diyAudio Member
 
Join Date: Feb 2013
Location: Netherlands
Wouldn't a signal (also DC) injected between the 318 and LM3886 be removed by NFB?
__________________
Regards Mark.
  Reply With Quote
Old 10th August 2014, 10:41 AM   #127
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Is the DC servo positive feedback?
The inverting input sees the injected error. this is inverted to become negative at the amp output.
Then inverted again in the servo and injected into -IN.
equals +ve feedback ??

Have I got too many invertings?
__________________
regards Andrew T.
  Reply With Quote
Old 10th August 2014, 12:53 PM   #128
UnixMan is offline UnixMan  Europe
diyAudio Member
 
UnixMan's Avatar
 
Join Date: Apr 2005
Location: Perugia + L'Aquila, Italy
Send a message via ICQ to UnixMan
Quote:
Originally Posted by Mark Whitney View Post
Wouldn't a signal (also DC) injected between the 318 and LM3886 be removed by NFB?
Yes. If the global NFB loop is active till DC (as it is here), the main NFB loop will try to restore any DC offset voltage present at input (times gain) at the output.

But the servo may be set up to have more gain (at DC) than the main loop, so that (at DC) it will "win".

In fact, by subtracting input village from the 3886, the servo will kill the "open loop" amp gain at DC (and subsonic frequencies).

Quote:
Originally Posted by AndrewT View Post
Is the DC servo positive feedback?
No, of course it must be NFB.

The servo integrator must be inverting or non-inverting depending on the injection point (in this case, which "side" of the HCP).

(After all the servo is nothing else than another loop of negative feedback, acting only at near-zero frequencies, and having 0V instead of the input signal as its reference or "input" so to speak).
__________________
Quote:
"We should no more let numbers define audio quality than we would let chemical analysis be the arbiter of fine wines." N.P.
  Reply With Quote
Old 10th August 2014, 01:27 PM   #129
diyAudio Member
 
lehmanhill's Avatar
 
Join Date: Jan 2008
Location: Chelsea, Michigan
Quote:
Originally Posted by UnixMan View Post
A similar approach could be to remove C9 and use a gyrator (a virtual inductor, of large value) in parallel with the global feedback resistor (same effect: bringing down to unity the gain at DC).
Interesting. I'm not familiar with a gyrator. Could you provide an example of point us to information on the gyrator?

Thanks in advance.
  Reply With Quote
Old 10th August 2014, 03:08 PM   #130
bcmbob is offline bcmbob  United States
diyAudio Member
 
Join Date: Dec 2009
Location: Bay City, Michigan
Mr. Elliot's take and the Wikipedia - Wow!!
__________________
Bob M.
"Arrange Whatever Pieces Come Your Way."
  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
My_Ref Fremen Edition - Build thread and tutorial ClaveFremen Chip Amps 2011 Yesterday 07:40 PM
My_Ref Fremen Edition RC - Build thread ClaveFremen Chip Amps 1250 19th September 2014 11:56 AM
My_Ref Fremen Edition GB (Second run) ClaveFremen Group Buys 52 22nd January 2014 09:13 PM
My_Ref Fremen Edition GB (interest for a third run) ClaveFremen Group Buys 107 13th January 2014 12:12 AM
My_Ref Fremen Edition - need help on PCB evaluation ClaveFremen Chip Amps 450 23rd October 2013 04:38 PM


New To Site? Need Help?

All times are GMT. The time now is 11:01 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