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Old 25th June 2008, 02:21 AM   #1
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Default Active filter design software

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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Old 25th June 2008, 03:41 AM   #2
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Default Re: Active filter design software

Quote:
Originally posted by lochness
I've never dealt with active crossovers so I don't know what sane values are.
Not these.

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.
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Old 25th June 2008, 09:27 PM   #3
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I figured that. I didn't know though.
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Old 25th June 2008, 10:39 PM   #4
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This any better?
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Old 25th June 2008, 11:14 PM   #5
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Considerably!
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Old 26th June 2008, 11:38 AM   #6
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Is it the same thing for the Low Pass filter?
I also need to mix the Low signals together. Is it just as easy as crossing the wires or do I need some sort of active mixer?
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Old 26th June 2008, 11:50 AM   #7
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Two resistors will do it. Look up "summing amplifier."

Yes, the lowpass will be just the inverse of the highpass. My advice, since your lowpass is only handling bass, is to just use a couple of opamps.
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Old 26th June 2008, 01:10 PM   #8
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Quote:
My advice, since your lowpass is only handling bass, is to just use a couple of opamps.
Oh but that takes the fun out of it.

So this is right for the lowpass?
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Old 26th June 2008, 01:13 PM   #9
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Where's the opamps????

Serious question: why a Bessel?
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Old 26th June 2008, 02:19 PM   #10
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Bessel is the default. I wanted a linkwitz-riley...must have hit the scroll thingy on the mouse before I took the screen shot.

no opamps as I have none on hand that aren't part of gainclones or some such. Tubes I have on hand.
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