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Old 22nd November 2009, 08:20 PM   #1
wicked1 is offline wicked1  United States
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Default passive xover w/ SET?

I've seen a lot of very mixed info about using passive speaker xovers and tube amps.
Im thinking about jumping on the open baffle bandwaggon, as I have a spare pair of ff85k full range drivers. I want to add a big high efficiency woofer w/ 1st order xover, so just one big inductor.
I read a post in the multi-way forum where a person could not get his speakers/xover to work on his tube amp, but his inductor had a high-ish DCR.(and totally different xover, and was also xover the full ranger which i wont do)
So anyway... is it possible to use a passive xover w/ tube amp w/ the right choke? I dont mind using a solid core inductor w/ low dcr, if that makes the difference.

Thanks!
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Old 22nd November 2009, 08:59 PM   #2
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IMO, your thinking about keeping the crossover simple is correct. However, I wonder about woofer to "full range" blending. Correct blending that allows the "FR" to roll off naturally, at the bottom, will require a mechanically LARGE inductance in series with the woofer's voice coil. I think you should consider 1 pole filters on both drivers, which have F3 set to a value that's well figured out.

Parts Express shows some cored chokes intended for "deep" bass service here. The largest value listed is 18 mH., which "turns over" at approx. 70 Hz. in series with an 8 Ω resistance.
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Old 23rd November 2009, 12:26 AM   #3
wicked1 is offline wicked1  United States
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I'll take your advice and look into the speaker and xover design more before I start.
I just wanted to make sure it wasn't a futile effort since I'm using a tube amp. The posts about it are truly quite mixed.
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Old 23rd November 2009, 04:01 AM   #4
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I have that "big" 18mH inductor from PE & it worked great on my 12" DVC sub. The RE of that sub speced at 3.2 Ohms & I was hoping the resonance would drive up the impedence so the amp wasn't seeing that heavy load..........worked fine. If the information that low is there, it will get thru.

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Old 23rd November 2009, 04:17 AM   #5
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I use series passive crossovers and have always used a tube amp.

We use a variety of oddball crossovers and tube amps at diyAudio Fest and not had problems.

Methinks you hear from people using incompetent tube amps or crossovers or both

Cheers!
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Old 23rd November 2009, 05:10 PM   #6
kevinkr is offline kevinkr  United States
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I think the issue is less with the X-O and more with whether or not the amplifier can deal with complex loads which is generally the case with multi-way speaker systems.

I drive my 3 way Onkens with passive X-O using a 300B SE with about 8Wrms output per channel and get very good sound.

The efficiency of the speaker system is such that you would think my 3Wrms 2A3 amp would have done as good a job within the constraints of the reduced output power, but it didn't. The really major differences between these two amplifiers were in the quality of the OPT, fixed bias operation in the 300B amp vs cathode bias in the 2A3, and the sophistication of the PSU. The 300B amplifier won on all counts. (And it will drive just about anything IME)
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Old 23rd November 2009, 05:50 PM   #7
wicked1 is offline wicked1  United States
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My favorite amp right now is the tubelab 300b, which I think is a solid design. I've got various other tube and SS amps that will certainly be used w/ them as well.

I set up a test baffle last night, and it has helped to see for myself how inefficient OB speakers are. It will be pushing my 7watt amp, but I think it's do-able.
I also don't believe the data on the little ff85k's.. The graphs that are posted in the speaker forums shows them going relatively deep, and people xover at 200hz or below, but I don't hear ANY bass out of them.. Not even relatively high pitched kick drums.. In my micro-fonken PC speakers, I have to xover my 'sub' at about 350hz. but I digress.. I'll talk about that in the appropriate place after Ive done more research and testing.

Last edited by wicked1; 23rd November 2009 at 05:53 PM.
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Old 23rd November 2009, 08:57 PM   #8
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ff85k is a 3/4" tweeter with a big surround - fuggetabbout any bass.

Planet10's "Tysen" is a crazy good implementation of that speaker.


Quote:
My favorite amp right now is the tubelab 300b, which I think is a solid design.
You bet! George doesn't even know how to design junk

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Old 25th November 2009, 02:19 PM   #9
wicked1 is offline wicked1  United States
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Ive got one more question on this topic..
It looks like I was mostly concerned for no reason about using a passive xover w/ tube amp.
I think you've already answered this, but I'm a little dense sometimes, so just want to spell it out before I order $100 in copper coils...

Is a low DCR for the inductor anything I really need to worry about at all? Nothing I'm looking at is too hight.. A laminated core will give me about .2ohms. I ran some models, and having a higher resistance inductor actually flattens my response a bit. So, I could use air core w/ a DCR of about 3ohms if the tube amp should be able to handle it.

And Eli, I ran some models last night w/ the ff85k run wide open, and various chokes on the woofer. You were right on track. My modeling shows about 12-15mh to be perfect (depending on dcr). It was a few decibel slope with about 40hz being the loudest, barely sloping down a few db to 20k. But, I don't think the ff8fk model matches it's real world performance... Ive got a feeling in real life the high end would be the slightly louder end.
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Old 25th November 2009, 09:56 PM   #10
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wicked1, sorry to go off tangent but if you are going through all this trouble, why not go with active crossover. Clarity, dynamic range and damping factor can all benefit from going active. It doesn't have to be a premade active crossover unit. Diy line level circuits are available (Elliott Sound Production) as well. Either that or you can design one like you are doing now. Just a thought.
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