Active XO with LM3886 as opamp - 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 5th August 2007, 04:59 AM   #1
diyAudio Member
 
xplod1236's Avatar
 
Join Date: Dec 2003
Location: On the couch
Send a message via AIM to xplod1236
Default Active XO with LM3886 as opamp

I'm building some 2 way speakers using Dayton drivers from Parts Express, which will be bi-amped. The idea here is to design a high/low pass filters with a gain of about 20, and use the LM3886 as the opamp and power amp in the filter. The drivers would be connected to the output of the filter (with built-in power amp). What are the pros/cons of doing it this way? One pro I can think of is less parts. Any comments and suggestions are welcome.
  Reply With Quote
Old 5th August 2007, 05:11 AM   #2
Account disabled at member's request
 
MJL21193's Avatar
 
Join Date: Mar 2007
Hi,
I'm working with a similar concept here:
Active filter plus LM3886 - one board

Good idea for a two-way, as you can really simplify things by using the amp as the filter.
Good luck.
  Reply With Quote
Old 5th August 2007, 06:02 AM   #3
diyAudio Member
 
Join Date: Dec 2001
Location: SIUE, Illinois, USA
The LM3886 is not unity gain stable. you will need to chose a topology with high closed loop gain that tolerates component errors with the higher gain. This does add some design difficulty that isn't present for unity gain stable opamps.
__________________
if only it could be used for good, not evil...
  Reply With Quote
Old 5th August 2007, 11:19 AM   #4
diyAudio Member
 
Join Date: May 2004
Location: Hertfordshire
The TDA2030A datasheet describes how to do active crossovers. You could substitute the LM3886 for the TDA devices on page 10 here:
http://www.st.com/stonline/books/pdf/docs/1459.pdf
Clearly the actual filter values would have to be tweaked to suit your particular drivers, but this satisfies Chris's criteria
  Reply With Quote
Old 5th August 2007, 02:31 PM   #5
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Hi Thechris,
the 3886 is configured for normal power opamp gain.
The preceeding but integrated filters use the unity gain concept. I wish he hadn't chosen unity gain, due the limited flexibility and complex maths involved in changing Q values.
He is effectively emulating a plate sub-amp that takes wideband source material and filtering it to actively drive individual narrowbanded speakers.
__________________
regards Andrew T.
  Reply With Quote
Old 5th August 2007, 02:56 PM   #6
diyAudio Member
 
Join Date: Oct 2003
Location: Europe-Asia
I've made "tri-phonic" system to my son some years ago, it use 1 LF channel and 2 MF+HF channels, but of course - it can be used with 2 LF speakers as "Bi-Amping".

Schematics: http://one.fsphost.com/altor/DIY_Hob...amplifier.html

text in russian, but schematics I hope are clear to understand.

I put 2 2nd order filters in serial, and the final stage - LM3886 based.

1st picture: volume control, LF-mixer, HighPass filters to sattelites.
2nd picture: phase invertor+phase shifter
3rd picture: Linkvitz transform and LowPass filter.
4th picture: 3886 output stage as the HighPass filter and High output impedance ("current source")
5th picture: 3886 output stage as the LowPass filter with negative output impedance.

Of course - you can use this 3886 filter schematics with the minor changes, if You don't want negative or high output impedance.
__________________
Regards, Alex
www.altor.co
  Reply With Quote
Old 6th August 2007, 01:18 AM   #7
Account disabled at member's request
 
MJL21193's Avatar
 
Join Date: Mar 2007
Quote:
Originally posted by AndrewT
Hi Thechris,
the 3886 is configured for normal power opamp gain.
The preceeding but integrated filters use the unity gain concept. I wish he hadn't chosen unity gain, due the limited flexibility and complex maths involved in changing Q values.
He is effectively emulating a plate sub-amp that takes wideband source material and filtering it to actively drive individual narrowbanded speakers.

Andrew,
I think you are referring to my project, when you made the above remarks. TheChris was actually (I think) referring to xplod1236's plans to use the LM3886 as the filter.
My unity gain filter sections are 4th order Linkwitz-Riley, which have (almost) perfect phase-coherency, with no peaks or dips at the crossover frequency.
I have no reason to change the Q or the crossover frequencies, as I am well within the capabilities of my selected drivers.
The best part of my design is it's low cost - about $12.00 for each completed stand-alone filter/amp unit. With the cost this low, it becomes disposable, if a change is needed.
  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
Opamp for active filter and preamp tpsorin Chip Amps 9 7th April 2008 07:23 AM
Opamp for active crossover Keruskerfuerst Parts 2 7th June 2007 06:57 PM
Active XOVER....OPAMP or discrete....??? Lyra Multi-Way 8 23rd March 2007 12:19 AM
Best Opamp for an active crossover? ShinOBIWAN Digital Source 1 21st March 2005 03:08 AM
Help choosing opamp for active filter Alcaid Parts 5 25th February 2004 09:50 PM


New To Site? Need Help?

All times are GMT. The time now is 09:48 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