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Old 20th February 2006, 09:01 PM   #1
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Default Active filter board GB

Looking for interest in a group buy of active filter boards.

WIKI

Each board will be suitable for a one channel two way will contain provisions for:

input buffer that can include BSC
4th order HP and LP
2 Notch/Peak filters
one output buffer with variable gain

I'd like to see added

2 All pass sections

If we add jumpers to allow re-ordering the sections, the notch filters could act as the output buffer on one stage.

Preliminary board layout HERE
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Old 20th February 2006, 09:15 PM   #2
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Interested! (And added to the Wiki)

Great work.
Harry
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Old 20th February 2006, 09:29 PM   #3
Nisbeth is offline Nisbeth  Denmark
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Added my interest to the wiki.

FWIW, an on-board PSU would be a plus for me but the all-pass filter option isn't something I think I have much use for


/U.
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Old 20th February 2006, 09:49 PM   #4
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See www.linkwitzlab.com/filters.htm (also the crossover page) for a dissertation on the utility of all pass sections. The nutshell version is that they allow you to correct for phase differences due to driver acoustic center offset and crossover induced phase shifts without resorting to staggered frequencies in the high and low pass sections.

I read SL's "Active crossover circuits that do not include phase correction circuitry are only marginally useable." as a bit of pomposity until I tried it. The difference was instantly recognizable on transients. (the drivers were old Focal coated paper woofers and kevlar tweeters) My disinterested then 13 year old son noticed right away when I added the all pass section and stopped playing his video game to listen. Transient attacks became sharper and clearer.

If you build properly sloped baffles you can get away without the all pass.

Maybe the board can grow a little and keep the regs while adding the all pass sections. Jens does the software you are using at home support this?
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Old 21st February 2006, 12:08 AM   #5
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For those wondering, this board is intended to be a final board. I suggested jumpers in the MOX thread as a way of making it flexible for a variety of projects, rather than adjustable. Some may need two EQs on a high pass section, some may use it as a bandpass, etc.

I envision that jumpers would be wires soldered in place rather than the adjustable set in the MOX
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Old 21st February 2006, 12:49 AM   #6
troystg is offline troystg  United States
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I'm in but my 500Mhz P2 PC is having a hard time with the Wiki...

I guess it's finally time to get that dual core 2.8 GHz I was looking at...

At least I upgraded OS from Windows 3.1 last yr.... LOL
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Old 21st February 2006, 12:52 AM   #7
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The Wiki is having "issues" at the moment...

500? That's 150 faster than my iMac!
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Old 21st February 2006, 12:56 AM   #8
troystg is offline troystg  United States
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Off topic but....

Pink mice and iMACs... Your a strange fella...

Can you feel the love Al?
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Old 21st February 2006, 01:00 AM   #9
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All the time, mate, all the time!

I'll have to check my finances, this looks like a good project.
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Old 21st February 2006, 02:59 AM   #10
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Just to save bouncing between threads, I have attached a spreadsheet for caclulating component values for HP, LP, shelving LP and notch/peak EQ sections
Attached Files
File Type: zip xo calcs based on jens rasmussen manuals rev1.zip (43.5 KB, 793 views)
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