Passive line-level crossovers

Discussion in 'Preamps' started by auri, Mar 20, 2017.

  1. auri

    auri Facebook Friend

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    I'm building a 2-way setup in my living room with 12" woofers and B&C DE250 in SEOS horns. I'd like to avoid passive crossovers. Just wondering if someone can make sure I'm on the right track?

    I understand why people go DSP, flexibility and ease of setup. In the quest for ultimate resolution though the idea of AD-DA conversion downstream of (or instead of) a nice DAC is horrifying, unless it was a $5k DEQX, in which case I still think I'd prefer an Yggdrasil...

    So I'm stuck with analog active or passive (PLLXO). I figure I'll start by getting a decent analog active like an Ashly XR-1001 to dial in my points, but to avoid op-amp hell I'll end up full passive.

    I've read the PLLXO guide and played around with the calculator but the basic set up seems fairly limited (12db slope, dependent on input impedance). What I'd really like to do is replicate a Marchand XM46 using inductors to manage the impedances with a 24db slope, except without paying $400 for fixed points without understanding enough to know how to adjust the values.

    But I'm not smart enough to figure out how to do it and I can't seem to find how anywhere. Any ideas?

    Thanks in advance.
     
  2. Armaegis

    Armaegis Friend

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    I'm pretty sure you can get a purely digital minidsp crossover and use your own dacs downstream of it. It'll be significantly cheaper than the DEQX.
     
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  3. auri

    auri Facebook Friend

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    Yeah the nanoDIGI. That's an option but then I'd have to run multiple DACs. Are two Bimbys worth one Gungnir Multibit? :eek:
     
  4. Armaegis

    Armaegis Friend

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    Well in this case... yes? You can do things in the digital crossover that you can't in the passive and will have far more flexibility. Is that worth a Bifrost Multibit to you?
     
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  5. auri

    auri Facebook Friend

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    The other option if I was going that way is to get a RME HDSP or similar (not Digigram, needs multi-channel, dunno about Lynx) and do everything with Equalizer APO, but I don't know if Windows would recognize multiple output devices. Should be easy to find out though if I wanted to go that route.

    I'm still stuck on multiple DACs though. What I meant was is hypothetically spending $1200 on two Bimbys worth one Gungnir Multibit when everything is done digital?
     
  6. purr1n

    purr1n Super Friend

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    That's the limitation of PLLXOs. You need a sky high input impedance on your amp for a high pass 12db / octave PLLXO, so this pretty much eliminates most solid-state power amps. One possibility is a hybrid passive line level and speaker level approach. One cap on the compression driver and a 6db / octave PLLXO, which might be feasible.

    Passive speaker level into horns isn't a bad as you think. Just two parts, a cap and a coil (and L-pad) will work. The crossover point is low enough that you don't need a Zobel.

    The real challenge is knowing what the frequency response of the horn / compression driver will look like and designing around that. There are a lot of tricks in playing with the values of the parts to get the desired response with minimal parts.
     
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  7. auri

    auri Facebook Friend

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    Yeah, I have the board sets to build a couple First Watt F5s, which happened to be one of the only ones I've found to have the input impedance I need (100k) so maybe I'll be revisiting full passive high pass in the future. The dumb little Lepai I have now is only 48k and everything else I have is even lower.

    I like the hybrid idea, but you're right, I shouldn't be that opposed to passive speaker level on the horns considering that the whole neighborhood would probably hear one watt. Hmmm.

    As for FR this is the exact combo I'll be running, and I have a bit of flexibility with my room so I might be able to do some good work killing reflections.

    [​IMG]
     
  8. purr1n

    purr1n Super Friend

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    Yeah, don't be afraid of simple crossovers. I'd add a circuit to shelve down 2-5kHz (typical with horns / waveguides). You might need a Zobel to right the rising impedance of a woofer crossed over at 800-900Hz to fight the woofer's rising impedance. With decent caps, I don't really notice a significant difference between no crossover and 5-6 part crossover. It's those 48 piece crossovers / networks that you need to be afraid of.
     
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  9. Cspirou

    Cspirou They call me Sparky

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