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Old 9th August 2008, 02:19 PM   #1
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Default Level control on op amp crossover

I am in need of an active crossover for my PA amplifier. I use it for keyboard and vocals. The amp is a Peavey XR600 powered mixer with two separate power amps. In normal operation you can select the main mix through both power amps or one for monitor and one for main.

It does have a main mix out and individual power amp inputs. Given the application it seems that opamps should be fine so I was going to build something like the attached 3rd order crossover (but using AC power supply).

However I realized that there is no provision for individual gain controls on the power amps. should I just add a 10K pot to each output (after the coupling cap) or do I need to add buffered gain controls at the input or output of the filters?
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Old 9th August 2008, 08:07 PM   #2
mikee55 is offline mikee55  United Kingdom
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Default hello mashaffer

http://sound.westhost.com/projects-3.htm

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Old 9th August 2008, 09:45 PM   #3
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Thanks, that two way looks very much like what I was doing with somewhat different values and buffers on both ends. I may just build that one as is adjusted for my crossover point.

I would end up using one quad and one side of a twin. Is it best to just ground the unused inputs and outputs?
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Old 9th August 2008, 09:49 PM   #4
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I use opamps that can easily drive something less than a 2k load, then use 2k pots on each output. Seems to work nicely and doesn't have any trouble with any reasonable cable length.
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Old 9th August 2008, 11:31 PM   #5
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I couldn't build one as nice as this for the price:

http://www.aiconsol.com/sx21-rolls.html

http://www.rolls.com/data/sx21man.pdf
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Old 10th August 2008, 12:19 AM   #6
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For what I need I can build it for about $5 for any caps that I don't have on hand so I will go that way. I have the PT, jacks, power cords, op amps, case, perfboard and case sitting in the junk box along with a bunch of carbon film resistors and some salvaged caps but not enough to be sure that I have all the cap values I need.
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