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Old 27th August 2004, 07:37 PM   #1
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Question Looking for an active crossover design (low pass only)?

Ok i know this isnt really an amp as the forum intention but it is the front end to one. I'm building a small active sub to go with some speakers I've built, but I was wondering if anybody had a design for a filter that would be low-pass only with vaiable crossover point and subsonic filter around 10Hz, Idealy with a small semi parametric eq as well? any help would be great other wise i'll be starting compleetly from scratch.
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Old 28th August 2004, 05:24 AM   #2
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This is an active low pass filter that has an adjustable Fc and has a 40dB per decade rejection. Simple op-amp circuit found in most electronics text books.
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Old 28th August 2004, 05:30 AM   #3
rkc7 is offline rkc7  United States
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I just designed and built an active crossover with 2 way stereo and subwoofer with subsonic filter and boost. I used the following pages to design all aspects of my crossover, including the power supply:

http://sound.westhost.com/project09.htm

http://www.snippets.org/filters/crossover.htm

I purchased parts from:

www.digikey.com, polypropylene capacitors, box, power switch

www.allelectronics.com, electrolytic caps, RCA input/output units (good deal), 16VAC transformer ($3.50!)

www.futurlec.com, metal film resistors ($0.20 to $0.35 for 10), misc capacitors, PCB board (I used stripboard), heatsinks

I used the power supply design from Snippets, 2-way from Sound.Westhost, and sub crossover boost from Snippets. In the end I combined parts of each website. I used the buffers from the first site for the inputs, used the Snippet's "Shiva" design to produce the active boost and lowpass for the sub. I did the mono summing after the buffers, then the lowpass, then the highpass subsonic boost.

I used the excel sheet on the Snippets website to calculate the component values I needed for the crossover, except for the buffer stage and output resistors which I used the info from the Westhost page.

I'm no expert, but it works for me. So, good luck!

Edit:

By the way, I started out with the same intentions as you, but eventually decided to just make a biamped system with sub for my high-powered PA/DJ style system and then found a Carvin 1000w amp for my sub and a Audio Centron 125w x 2 for the high on Ebay, all together costing me less than $170 for the extra amps and then $60 for the crossover. Overall, it's not that much more expensive to just make a biamped system, and many will argue it's much better. I haven't yet been able to fully experience my efforts (college is interfering), but I'm sure I'll be very happy!
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Old 28th August 2004, 06:08 AM   #4
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You know if you just expand this circuit out, make 11 or more bandpass filters, use a slide pot as a voltage devider for each bandpass to adjust that specific frequency, you would have a pretty good EQ. Just adjust the RC componants for the proper Fc low and Fc high for each bandpass filter. Lots of surface quad op-amp chips, small capacitors, resistors, and soldering skills needed for this though. If you got the skills and the time, you can make an EQ as accurate as you want.
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Old 28th August 2004, 07:38 AM   #5
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Thanks guys. This should get me on my way. Its probably going to take me a few weeks to get anything done due to work restraints however, I'll let you all know how I get on and what mods etc i do.
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Old 28th August 2004, 12:25 PM   #6
lucpes is offline lucpes  Europe
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This might be of some use, too: http://www.analog.com/Analog_Root/st...er/filter.html
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