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In Reply to: RE: Try this calculator, maybe. posted by pictureguy on June 24, 2015 at 16:15:14
I think the calculator will still give the correct values, you'll just be putting in your amp input impedances instead of the speaker impedances. Again, someone please correct if I'm wrong. The values seem to come out as they should.
Mark in NC
"The thought that life could be better is woven indelibly into our hearts and our brains" -Paul Simon
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The PLLXO schematic I've see has NO inductors, let alone the 3.5mh monster used in the low-pass element of the 1.6
Buried in the link is the line-level schematic from DAVEY, to whom i credit with letting me think I could pull this off.
The circuit shown is for 39k input impedance. Cap values are VERY small and setup / layout are important.
Too much is never enough
The cap values should simply be adjustable in proportion to the input impedance of the tweeter power amp - Cnew= Cold * 39k / Ri
I would drop the resistor L pad in favor of a good quality 10K cermet or wirewound pot used as a variable resistor so you can tune the XO to the subjective balance that suits your system room and taste.
The low pass section should stand on its own unless the output impedance of your preamp is unusually high.
Thanks: Good answer.
I was thinking just that, at least in part. A speaker with 8 ohms needs (say) 22uf while the listing for Davey's schematic shows NF for a 39k impedance. So, for my 33k, the caps should be a little larger. I'll sit down later and 'do the math'. If I think the answer makes sense, I'll run it by here.
As for a variable resistor? I'm not in love with 'em. They all end up noisy and unless all the way CW or CCW, difficult to repeat settings. I'm inclined to try a 3 or 4 way SWITCH and resistor net, if that's feasible.
Still Noodling.
Too much is never enough
You are right and a switched resistor will give a better result, you need at least a 5-6 position switch to give you + / - 3 to 6 db range at good intervals, but you can also get a rotary scale that can allow repeated settings on a pot.
And I can't get it straight?
Use a 'make before break' or 'break before make' switch?
Too much is never enough
If you get a discrete resistor vol control you will have a quiet switch having been chosen for the role. There are decent dact knockoffs on Ebay though I don't remember which vendors are any good, you need to look it up.
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