Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Chip Amps Amplifiers based on integrated circuits

LM3886 gainclone DC servo
LM3886 gainclone DC servo
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 27th October 2017, 12:05 PM   #1
belyakove is offline belyakove
diyAudio Member
 
Join Date: Jan 2017
Default LM3886 gainclone DC servo

Hi. I recently ordered 6xLM3886 BPA300 pcbs from Jim's Audio. Schematic says that there are OPA2604 used for DC servo and also as a balanced line driver that converts input signal. Unfortunately I can't find exactly these opamps in my area. So the question is, can be some other opamp (like OPA2134) used instead? Should any values of surrounding elements be changed in this case?

I can post schematic if that helps in this case.
Thank you.

Last edited by belyakove; 27th October 2017 at 02:59 PM.
  Reply With Quote
Old 27th October 2017, 02:02 PM   #2
belyakove is offline belyakove
diyAudio Member
 
Join Date: Jan 2017
Sorry, accidentally posted this in solid-state. Can it be moved to chipamp theme
  Reply With Quote
Old 27th October 2017, 02:08 PM   #3
Pano is offline Pano  United States
diyAudio Moderator
 
Pano's Avatar
 
Join Date: Oct 2004
Location: SW Florida
LM3886 gainclone DC servo
Moved
  Reply With Quote
Old 27th October 2017, 08:01 PM   #4
ICG is offline ICG  Germany
diyAudio Member
 
Join Date: Jul 2007
Location: Too many amps, too many speakers, too little time
For the functionality, yes, you can swap them. That works mit most FET OPamps. The OPA2604 are especally designed for audio though and other OPs will most likely sound differently. An example how different it can be is this YT-video. It does not compensate for the different gain which causes the AD712 to distort (more) but it's IMO still audible (or at least partly) that the OPA2604 got much better details. That is ofcourse depending on the circuit and not 1:1 transferable to other applications. However, it does show there actually are differences between the OPamps.

To substitute the OPA2604, you have to look at other FET OPamps, bipolar ones will not work correctly here since they will introduce DC offset, the servo will definitively not work as intended. I don't have much experience regarding FET OPs replacement in audio, the TL072 and TL082 will work though. As an alternative for OPA2604 it would be better to use special designed OPs for audio like the OPA1679, which is cheap and 'able' FET OP but I don't know about the availability or price in your area (where are you from?).

If you can't get these I would socket the OPs an try with standard (available) FET OPs like the TL082 and swap it later if you aren't satisfied.
__________________
After all is said and done, usually more is said than done.
  Reply With Quote
Old 27th October 2017, 08:07 PM   #5
asuslover is online now asuslover  Romania
diyAudio Member
 
Join Date: Aug 2016
Location: USA
Can u post schematic (from jim's) for that amp plz?
Thanks
  Reply With Quote
Old 27th October 2017, 08:11 PM   #6
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
LM3886 gainclone DC servo
The OPA2604 is no longer produced due to problems in production, apparently the later devices degraded and dropped out of spec when used at high supply voltage.

The TL072 is ideal for a servo, and in any case no audio appears at the servo output.

For audio it is actually still a good choice... try it.
  Reply With Quote
Old 28th October 2017, 01:07 AM   #7
belyakove is offline belyakove
diyAudio Member
 
Join Date: Jan 2017
Here are the schematics of one amp block and balanced line driver based on OPA2604.

Thank you for replies. Are any changes to surrounding elements of dc servo needed? I am confused because in TI's AN-1192 application which describes BPA200 circuit different values of those elements and different opamps are used and I thought they might need to be different if I'm going to swap OPA2604 for something else.

By the way, I live in Netherlands
Attached Images
File Type: png Screen Shot 2017-10-28 at 02.00.36.png (44.2 KB, 285 views)
File Type: png Screen Shot 2017-10-28 at 02.00.48.png (46.0 KB, 285 views)
File Type: png Screen Shot 2017-10-28 at 02.15.32.png (40.1 KB, 279 views)

Last edited by belyakove; 28th October 2017 at 01:18 AM.
  Reply With Quote
Old 28th October 2017, 01:59 AM   #8
ICG is offline ICG  Germany
diyAudio Member
 
Join Date: Jul 2007
Location: Too many amps, too many speakers, too little time
A DC servo is self-regulating per definition. That means, this function will stay the same as long as the used OPs are within the intended operation value ranges. The OPs differ in gain, noise, slew rate, maximum voltage etc, so there will be a difference but i.e. gain is not an issue in your case, neither is maximum voltage and DC offset is not an issue originating from the FET OPamps either anyway. That does not mean you can ignore a DC offset check before use though, that should always be done.

The BPA200 works a lot different than the LM3886 gainclone, it is designed as a bridged/parallel bridged amplifier. Following that, ofcourse it looks different and the values have to be different too if you are going to feed multiple ICs (BPA200: four ICs) because the design goals are different in priority. And there are more than just strictly one way (and one set of values) to achieve a desired result.
__________________
After all is said and done, usually more is said than done.
  Reply With Quote
Old 28th October 2017, 09:32 AM   #9
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
LM3886 gainclone DC servo
The TL072 will drop straight into both circuits, no changes needed. The LM3886 is missing a feedback return, it would not be stable at unity gain as shown.
  Reply With Quote
Old 28th October 2017, 12:23 PM   #10
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Quote:
Originally Posted by belyakove View Post
Here are the schematics of one amp block and balanced line driver based on OPA2604.

Thank you for replies. Are any changes to surrounding elements of dc servo needed? I am confused because in TI's AN-1192 application which describes BPA200 circuit different values of those elements and different opamps are used and I thought they might need to be different if I'm going to swap OPA2604 for something else.

By the way, I live in Netherlands
I don't think those chipamp schematics are correct.
take away the DC servo loop.
What is left is a 22k feeding back into the -IN node.
The feedback lower leg impedance/resistor is missing?
As shown you have a gain of 1 Follower that will be unstable.
__________________
regards Andrew T.

Last edited by AndrewT; 28th October 2017 at 12:32 PM.
  Reply With Quote

Reply


LM3886 gainclone DC servoHide 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

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
LM3886 Servo Design Redshift187 Chip Amps 67 3rd September 2017 12:13 PM
LM3886, XO, Buffer and Servo jackinnj Chip Amps 3 30th October 2008 01:14 AM
Gainclone LM3886 DC servo peranders Chip Amps 10 24th March 2004 05:59 PM


New To Site? Need Help?

All times are GMT. The time now is 05:12 PM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.00%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright ©1999-2017 diyAudio
Wiki