Chips for active cross overs - 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 1st April 2010, 05:17 PM   #1
ChrisA is offline ChrisA  United States
diyAudio Member
 
Join Date: Jan 2008
Default Chips for active cross overs

I want to build some bi-amped studio monitor type speakers.

I'm thinking of a conventional design. There will be a balanced XLR input that goes to a buffer then to a 24db/octave low and high pass filters. Each filter drives a conventional LM3386 chip amp that connects to either a woofer or tweeter.

Question about the filters: Before I wire up a cascade of TL074 op amps and many precision passive parts is there some "filter chip" available that would make the design simpler? I figure there are so many bi-amped monitors on the market that someone might be offering an integrated active crossover chip. Although the TL074 does come in a quad package so it is not to bad.

Are any better op amps than TL074? It was the preferred part last time I looked, years ago.

Last edited by ChrisA; 1st April 2010 at 05:24 PM.
  Reply With Quote
Old 2nd April 2010, 04:06 AM   #2
diyAudio Member
 
Join Date: Jun 2009
I looked for such chips a couple months ago. There are a few around, but none worth pursuing for crossover use. Unless you count things like Analog Devices' SigmaDSP family.

For audio op amps National's LME49990 is damned tough to beat. The more affordable LME49710/49720/49740/49860/49870 series is a close second.
  Reply With Quote
Old 2nd April 2010, 06:21 AM   #3
Calvin is offline Calvin  Germany
diyAudio Member
 
Calvin's Avatar
 
Join Date: Nov 2004
Location: close to Basel
Hi,

it all depends on the intended usage and Im pretty sure that there are quite a few OP amps that are cheaper and better suited for filter applications than the National-Brand, i.e JFET-Input-OPs.
What makes You think that the LME49990 is so exceptional?
Any reason why should it sound good??

jauu
Calvin
  Reply With Quote
Old 2nd April 2010, 04:11 PM   #4
diyAudio Member
 
Join Date: Jun 2009
Taking a look at the THD/IMD, CMRR, PSRR, and GBP specs on the 49990 (follow the link above and click on datasheet) should answer your question. For DC servos JFET devices like the TL071 family are attractive for their combination of low input bias, decent linearity, and sufficient gain bandwidth for the application. But for main signal path use I'm not aware of any JFET parts with linearity, bandwidth, or rejection abilities comparable to the 49710 family or 49990.

Granted, the 49740 is 10 times the price of a TL074. For a stereo LR4 crossover that's an extra USD 16, USD 20 if you include the 49710/TL071 to provide a fifth op amp for diff to single ended conversion in this case. Not a big deal, IMO, when building in DIY quantities.
  Reply With Quote
Old 2nd April 2010, 04:40 PM   #5
diyAudio Member
 
Join Date: Mar 2007
Location: California
Default Filter Chips

Yes, there are lots filter chips that could be used. Many are switched capacitor types that I would avoid... but there is one standout:

I have used and I can highly recommend the Burr-Brown UAF42. Each IC contains a second order HP+LP stage plus one uncommitted op-amp. The IC has on-chip 0.5% (IIRC) tolerance capacitors. They can be cascaded for higher order or for multi-way crossovers. External resistors set crossover frequency and Q across any values that you would need for audio work. I recommend using the inverted configuration. Specs are good. This is much better IMHO than building your own using op amps because of the on-chip capacitors and the ability to re-use the IC (it is a DIP14, so just put it in a socket) in various ways/projects.

-Charlie
  Reply With Quote
Old 2nd April 2010, 04:54 PM   #6
diyAudio Member
 
analog_sa's Avatar
 
Join Date: Aug 2002
Location: Sofia
Quote:
Originally Posted by CharlieLaub View Post
This is much better IMHO than building your own using op amps because of the on-chip capacitors
The on-chip capacitors make me think it's much worse soundwise. Not to mention the on-chip opamps
  Reply With Quote
Old 2nd April 2010, 04:55 PM   #7
diyAudio Member
 
Join Date: Jun 2009
Or, if you want an alternate opinion, I rejected the UAF42 because of its limited GBP and a distortion spec that didn't meet my end to end budget.
  Reply With Quote
Old 2nd April 2010, 05:19 PM   #8
ChrisA is offline ChrisA  United States
diyAudio Member
 
Join Date: Jan 2008
Quote:
Originally Posted by twest820 View Post
Taking a look at the THD/IMD, CMRR, PSRR, and GBP specs on the 49990 (follow the link above and click on datasheet) should answer your question. For DC servos JFET devices like the TL071 family are attractive for their combination of low input bias, decent linearity, and sufficient gain bandwidth for the application. But for main signal path use I'm not aware of any JFET parts with linearity, bandwidth, or rejection abilities comparable to the 49710 family or 49990.

Granted, the 49740 is 10 times the price of a TL074. For a stereo LR4 crossover that's an extra USD 16, USD 20 if you include the 49710/TL071 to provide a fifth op amp for diff to single ended conversion in this case. Not a big deal, IMO, when building in DIY quantities.
Thanks. I was the one to ask this question. I can buy TL074 in surface Mount SOIC packages for $0.21 each. That is five cents per op amp. I see a 49740 for $6.50 in SOIC-14 package or $13 per channel, not bad (but $0.42 is better.)

But I'm still surprised that there are no x-over chips. I wonder what is inside all the M-audio, Mackie, Focal, and so on bi-amped monitor speakers. I can't imagine they use 8 or 10 op amps and two chip amps per speaker and still sell and their price. I'd bet there is a highly integrated part in there.

As an example this is bi-amped with 18db x-over and retails for $150
Buy KRK Rokit Powered 5 Generation 2 Powered Studio Monitor (Each) | Powered Monitors | Musician's Friend

Last edited by ChrisA; 2nd April 2010 at 05:38 PM.
  Reply With Quote
Old 2nd April 2010, 06:43 PM   #9
diyAudio Member
 
Join Date: Jun 2009
I think your expectations may be a bit high. Even fairly high end pro audio stuff I've taken apart relies on large numbers of op amps like the NJM4565. Haven't ever looked inside a Rockit but my experience is 18dB slopes are usually line level passive crossovers that are marketed as active solely on the basis the crossover is located in front of the power stage. Most likely just a two channel 8 SOIC input buffer with strings of 0402 resistors and caps between it and the power stages. So far the stuff I've taken apart that was marketed as LR4 has actually had Sallen-Keys in it, but it wouldn't suprise me if some of it's just RCRCRCRC.
  Reply With Quote
Old 2nd April 2010, 06:55 PM   #10
diyAudio Member
 
Join Date: Jun 2009
Forgot to mention, Charlie, if you want exact matching between channels consider state variable filters. At some point it becomes less hassle to switch to a digital crossover, though.
  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
Disabling cross overs and bass boost on ppi pc450 geom_tol Car Audio 5 26th July 2007 01:05 AM
Building Subwoofer Cross Overs? Dominick22 Subwoofers 15 22nd September 2006 08:15 PM
Capacitors for Cross-Overs 2x6spds Parts 1 14th November 2005 01:13 PM
Active vs. Passive X-overs Pete H Multi-Way 60 7th June 2005 04:08 PM


New To Site? Need Help?

All times are GMT. The time now is 06:20 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