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Active filter design software

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Been playing with TJC Filter software. I don't really know what sane values are for the different components. Wanted to use some 12av7s for this.
As far as I can tell you can't adjust the voltage provided to the tubes only what tubes you are using and the other various components.

This is what I've got so far. I've never dealt with active crossovers so I don't know what sane values are.
 

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lochness said:
I've never dealt with active crossovers so I don't know what sane values are.

Not these. :D

The cathode followers are horribly loaded down, trying to drive 225 ohm resistors. And the 900 ohm resistors will throw off an impressive amount of heat right up until your power transformer melts.

Try making the coupling caps more like one or two nF. That will cause the resistors being driven to be more like a few hundred k-ohm, a more reasonable load and large enough to swamp out the tubes' source impedance. The divider resistors can be anything from 100k on up, just so long as they're matched.
 
A couple of TL072s will set you back about $2 at Radio Shack. And (dirty secret time) they'll work fine for bass.

The other thing I'd give you a heads-up about (and my apologies if you already have thought this through) is the difference between electrical and acoustic response. Your lower driver ought to be flat to at least 800Hz (for your 200Hz crossover) and the upper driver should be flat down to 50Hz or so in order for the crossover to work as planned.
 
OK, then I'll get more pedagogical. The overall acoustic response is the product of the crossover response and the response of the speaker/box/room. That can be pretty useful. For example, let's say you have a satellite, sealed box, that has an fo of 70Hz with a Butterworth (Q=0.707) response. That will be a second order rolloff, because it's a sealed box.

Now, you want to interface it with a subwoofer. One thing you can do is use a second order high-pass filter on the satellite that has electrically the same 70Hz fo and the same Q=0.707. Then the overall acoustic response will be fourth order at 70Hz. And not-so-magically, the response will be Linkwitz-Riley. Now with a 4th order Linkwitz-Riley low-pass for the woofer, what looks like an asymmetrical electronic crossover (2nd order Butterworth on top, 4th order LR on bottom) becomes a symmetrical acoustic crossover, and all is well in the world.

If the drivers have acoustic rolloffs within a couple octaves of a relatively shallow electrical crossover, the response will be affected; with some experimentation (e.g., time delay, moving the LP frequency down slightly...) it might be able to be overcome, but I think it's easier to pick a more appropriate crossover point and use the speakers' response to make like easier.
 
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