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Old 18th July 2012, 06:09 PM   #1
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Default xm46 passive crossovers

I have been successfully using 2nd order PLLXO's using capacitors and resistors for my bass amp and main amp.
Having played with an active crossover i feel that a 4th order crossover may offer some improvement in SQ, and potentially allow me to drop the crossover frequency of my mid range horn ( my logic is that as the slopes are steeper i can get closer to Fc)

I felt that the active crossovers took something away from the sound, preferring my PLLXO's over active ones of the same configuration.

This brings me onto Marchland xm46 crossovers, 4th order crossovers without the insertion losses as using inductors instead of resistors. Has any one got any experience of these, advise etc.
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Old 19th July 2012, 03:10 AM   #2
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Interesting. I hadn't seen these before. Gets around the size problem of the requirement for huge inductors using cored ones (which makes sense as they won't tend to suffer the same problems as inductors used at speaker level).

One thing I'm not sure of however is how they deal with the input impedance of the amp it is being connected to, I assume you would need to specify this at time of order. A lower input impedance is going to result in smaller coils required I would think.

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Old 19th July 2012, 01:47 PM   #3
Davey is offline Davey  United States
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Phil has had that unit out for a few years now.
The component values are such that most nominal loads will not skew the xover frequencies very much. But, he does specify a minimum 10k load impedance.
The (potentially) large issue with the XM46 is the fairly low load resistance presented to the source. (Approximately 1k.) Maybe some type of headphone amplifier would be a good source for it.

Cheers,

Dave.
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Old 19th July 2012, 04:10 PM   #4
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my source is a WOT preamp with a 600 ohm output, going into the (bass) SS amp @ 22k and 100k into the main amp, so should be okay driving, but preamp may be an issue?
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Old 19th July 2012, 05:27 PM   #5
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Possibly. You'd need to measure to confirm.
The 600 output resistance loaded by 1k ohm will yield about 4 db of attenuation even in a best case scenario.
If you have considerable capacitance in your interconnects you might create a low-pass filter that would dip into the audio region.

Cheers,

Dave.
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Old 20th July 2012, 07:36 AM   #6
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The insetion loss i can live with. The low pass filter element i need to understand better, where in the freq range would it be. Doing a bit of digging on the web i might be working out the load impedance wrong - i have considered each amp seperately, only worrying about the amps impedance for the high pass filter, ignoring it as the main valve amp is 100K, and the effects second order. The suggestion is that as the amps are in parallel then treating them as a reistive load the effective load impedance seem is now 1/(1/22K +1/100K) only 18K which is significant (even worse if tri-amped)

From my ignorant understanding it seems this arrangement will only work with a SS preamp and valve amps with high input impedance
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Old 20th July 2012, 03:31 PM   #7
Davey is offline Davey  United States
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No, your amps are not in parallel.

I don't believe your amplifier input resistances are an issue here since the XM-46 component values are such that the selected crossover frequencies will be maintained.
The effective load of the XM-46 on your preamp/source is what I was referring to. If your interconnects are sufficiently short and not some weird high capacitance design you should not have a filtering issue.

You'll need to increase your preamp output (volume control) by approximately 4db relative to an existing configuration. If your preamp has sufficient gain you should be fine.

The XM-46 should work okay.....assuming there are no other variables or parasitic or unknown factors.

Cheers,

Dave.

Last edited by Davey; 20th July 2012 at 03:33 PM.
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Old 20th July 2012, 06:26 PM   #8
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i would be integrating the crossover into my pre-amp, so those leads should not be an issue. I use 75ohm transmission line for interconnects so should be low capacitance.
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Old 20th July 2012, 06:40 PM   #9
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IIRC r2 is 5k, which means R1 is likely 1k. You need a preamp with a low output impedance and some grunt to drive these.

dave
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Old 14th August 2012, 08:00 PM   #10
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Sorry for not responding but been busy ( slave to the wage)

I have been looking further into these crossovers as my simple RC passives are not doing what i throught they were, but have some strange slewed slopes. The setup is as Click the image to open in full size..

My logic is until i understand this i wont be able to get a RCL crossover to work, correct me if i am wrong. I found this web page which almost has what i will eventually want to do Réalisation, simulation P(Spice) d'une chaine HIFI tri-amplié © Noel Loutre 2004 . However with this i am not the wiser as i don't understand how he is accounting for input and output impedance.
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