Active Filter

ChevS-10 · 24th June 2005, 05:21 PM

I've already posted a thread on the car audio, but I couldn't get my questions answered. I plan on making an active filter to filter a signal below 250 hz. for my front speakers. Someone suggested I use a passive filter, but I can't find the capcitance of the high pass on the two-way speaker. First question, will the opamp serve as a buffer between the RC circuits, meaning the highpass in the speaker and the Rc circuit before the opamp? Second question, I want a gain of one on the filter, so will I need to place a positive/negative DC signal on VCC & VEE of the opamp? I appreciate your assistance.

BobEllis · 24th June 2005, 05:48 PM

Not sure what you are asking. Are you trying to make a high pass to send everything above 250 Hz to your two way speaker or a two way active crossover?

Unity gain does not depend on rail configuration. Suitable op amps and circuitry can have unity gain from a single rail.

patience is a virtue - You'll get better results if you don't get insulting when your question isn't immediately answered, as you did in the car audio forum.

ChevS-10 · 24th June 2005, 06:20 PM

Bob, I'm sorry if you take me saying I hope I didn't stump anyone as insulting, but if you noticed I added a second question to the thread. This was the goal of the second post.

Quote:

Hope I didn't stump anyone, the thing I have a hard time believing is that with all the semi-conductors in an opamp that the one cap could possibly overcome that. One other question, that hopefully will get answered. If I want a gain of one on the Opamp do I need to apply the positive/negative DC to VCC & VEE.

You jogged my memory, correct me if I'm wrong, I need to use the correct resistances to make the correct unity gain.

Also, all I'm looking for is a filter. Not an active crossover. I know the basic configuration I want, but I just would appreciate any knowledge on the subject.

Thanks guys.

BobEllis · 24th June 2005, 06:31 PM

take a look at Rod Elliot's site www.sound.westhost.com for some filter info - this is an active crossover, of sorts, just that you only have the high pass section. Now you need to decide what order you need, and build on Rod's building blocks.

Unity gain opamp filters are easy - output ties directly to to the inverting input. an RC to the buffer non-nverting input gives you a second order filter. Rod has a handy dandy LR filter calulator on his site to help you choose the component values.

Just remember that for single rail operation you'll need capacitor coupling and a virtual earth.

ChevS-10 · 24th June 2005, 06:35 PM

Thanks.

24th June 2005, 05:21 PM	#1
ChevS-10 diyAudio Member Join Date: May 2005 Location: Appleton	Active Filter I've already posted a thread on the car audio, but I couldn't get my questions answered. I plan on making an active filter to filter a signal below 250 hz. for my front speakers. Someone suggested I use a passive filter, but I can't find the capcitance of the high pass on the two-way speaker. First question, will the opamp serve as a buffer between the RC circuits, meaning the highpass in the speaker and the Rc circuit before the opamp? Second question, I want a gain of one on the filter, so will I need to place a positive/negative DC signal on VCC & VEE of the opamp? I appreciate your assistance.

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Active Filter Four help	Cobra2	Solid State	9	21st April 2009 11:00 AM
I need an active sub filter!	hernanstafe	Subwoofers	18	4th December 2007 10:32 PM
active filter from rod elliot and sub filter questions	wuffer	Parts	0	2nd October 2005 02:12 PM
active filter	k1jroth	Chip Amps	50	1st December 2004 05:15 PM
looking for active filter sim	P.Lacombe	Everything Else	0	2nd January 2003 10:33 PM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read


	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

24th June 2005, 05:48 PM	#2
BobEllis diyAudio Member Join Date: Sep 2003 Location: Upstate NY	Not sure what you are asking. Are you trying to make a high pass to send everything above 250 Hz to your two way speaker or a two way active crossover? Unity gain does not depend on rail configuration. Suitable op amps and circuitry can have unity gain from a single rail. patience is a virtue - You'll get better results if you don't get insulting when your question isn't immediately answered, as you did in the car audio forum.

24th June 2005, 06:31 PM	#4
BobEllis diyAudio Member Join Date: Sep 2003 Location: Upstate NY	take a look at Rod Elliot's site www.sound.westhost.com for some filter info - this is an active crossover, of sorts, just that you only have the high pass section. Now you need to decide what order you need, and build on Rod's building blocks. Unity gain opamp filters are easy - output ties directly to to the inverting input. an RC to the buffer non-nverting input gives you a second order filter. Rod has a handy dandy LR filter calulator on his site to help you choose the component values. Just remember that for single rail operation you'll need capacitor coupling and a virtual earth.

24th June 2005, 06:35 PM	#5
ChevS-10 diyAudio Member Join Date: May 2005 Location: Appleton	Thanks.

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)