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EAW KF300 Tri-amping filters

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ModdFX View Drop Down
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    Posted: 06 September 2022 at 9:11am
Part of the passive crossover network burnt out in one of my KF300 3ways and I decided to try tri-amping it, bypassed the whole network and went straight amps to drivers.

Butttt...the hiss on the HF horn is now out of control, is there some sort of filter roll off I should be putting inline with it, or a passive limiter to protect the driver? Or both. Newb question.

I think I opened up more high end on it, but the manufacturer probably care more about volume and durability than anything, hence why their crossover seems to roll off some highs.

Edited by ModdFX - 06 September 2022 at 9:14am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote madboffin Quote  Post ReplyReply Direct Link To This Post Posted: 06 September 2022 at 12:18pm
Have you worked out the correct balance in levels between the hi, mid and low signals, or have you just applied filters?

You need to set the levels to account for the relative efficiency of the units.

For a typical 3-way box with horn loaded mids and tops, the HF horn will need less drive than the mid, and the LF cone will need more. If you run all at the same level the HF will be far too loud (and easy to blow up).

You should also have a suitable capacitor in series with the HF driver to protect it from inadvertent application of the wrong band, or from amplifier hum resulting from a dodgy connection.

HTH.


Edited by madboffin - 06 September 2022 at 12:19pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Conanski Quote  Post ReplyReply Direct Link To This Post Posted: 06 September 2022 at 2:04pm
The spec sheet suggests there is a 9dB difference in sensitivity between the LF and HF drivers so the output driving the HF needs to be turned down that much, and I bet that will take care of most of the hiss. The other thing you can do is use something other than a class D amp to drive the HF section as that type of amp typically produces the most self noise, a small(200w) class AB amp would do the trick.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote fatfreddiescat Quote  Post ReplyReply Direct Link To This Post Posted: 06 September 2022 at 2:37pm
Another solution is to add a power resistor in series to pad down the CD level and an inductor after the resistor in parallel with the CD, that will also damp the diaphragm and act as a protective high pass filter. It would also be driven current drive which may reduce harmonic distortion.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ModdFX Quote  Post ReplyReply Direct Link To This Post Posted: 07 September 2022 at 2:17am
The trouble is hiss from the amp >cable >driver, there is no passive network between them now to intercede since I hardwire bypassed it inside the cabinet. My BSS omnidrive is muted I am using an EV q44 (200w at 8ohms) for the 1" RCF n482 CD rated at 90w program.

I have another q44 (200w at 8 ohm) on the 6" RCF 380 midrange woofer rated at 150w program and a MC2 T1500 (625w @ 8ohm) on the 12" ATC woofer rated at 300w program. 

It seems like I need to re-introduce some sort of protection and roll-off via a vastly simpler network than EAW built into the box, at least for the CD and probably also the 6".

Anyone have a good source for schematics and resources on designing such a circuit? 


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Post Options Post Options   Thanks (0) Thanks(0)   Quote Earplug Quote  Post ReplyReply Direct Link To This Post Posted: 07 September 2022 at 9:52am
If you're getting hiss from the amp with everything else muted, the amp might be the problem! Have you tried a different amp? Or does it still hiss if the amp volume is turned to 0, or only when it's at 0dB?

And you should be able to do all the correction you need from the BSS. Don't bother with any passive circuit. At most, stick in a blocking capacitor, but that needs to be set with a roll-off at least an octave below your xover frequency. Nothing to do with rolling off the HF. My bet is on the amp.  Smile


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