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Old 19th December 2003, 05:25 PM   #81
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It may be appropriate to post this schematic here, which is an older version of Mr. Pass crossover (PCX). Additional info, with module pics can be found here: http://www.diyaudio.com/forums/showt...7444#post37444

I've been thinking about an active crossover for years, somehow never build a good one though. Probably because of Fred's thread, I'll be able to do it now
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Old 19th December 2003, 10:19 PM   #82
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You should have a unity gain buffer between the first order and second order section to prevent tuning one network from
changing the response of the other. Some
of the cookbook component values take in to account the interaction between the first and second order networks in the formulas but I think the intereaction could be a problem when trying to tune the first and second order sections to have different corner frequencies from each other.
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Old 19th December 2003, 10:54 PM   #83
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> You should have a unity gain buffer between the first order and second order section to prevent tuning one network from
changing the response of the other. ...I think the intereaction could be a problem...


For hand-tweaking a filter today, I agree. A buffer sure makes things easier.

But back in 1988, op-amps cost money and good audio op-amps were expensive (see inset in Peter's post; these were discrete hand-built hand-trimmed units). More design pencil was a good trade-off for fewer amplifiers.

BTW: Thanks for the thread.
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Old 22nd December 2003, 11:11 AM   #84
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Old 6th January 2004, 11:47 PM   #85
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Fred,

Thanks for the resistor matrix. Good job.

There have been Active Crossovers started in the past but none that I know of have gained enough momentum to finish. I've ordered some 2sk389 and 2sk170 to experiment with and gain some more knowledge. I dont know what Nelson has in store for his active crossover, but a PCB offering is something I would be interested in, or at least a layout to use for etching my own.

Most of all I wanted to bring this thread back to the top so it won't lose all its momentum.

BDP
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Old 6th January 2004, 11:56 PM   #86
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What seems interesting, reading technical description of Rushmore on PassLabs site, is that only first and second order filters were used in a passive way
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Old 8th January 2004, 06:16 AM   #87
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The bottom end is 2 pole, with 1 pole active, the mids are
single pole (6 dB/oct) passive, and the top is 2 pole
passive.
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Old 8th January 2004, 06:52 AM   #88
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It also says that "the cone drivers are direct coupled to the amplifiers with no intervening passive circuitry". Does that mean that Raven tweater is capacitively coupled to the amp for protection?

I found Rushmore literature very enlightening and will modify my main speakers into a similar setup
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Old 9th January 2004, 12:48 AM   #89
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It also says with no feedback, Followers? Does passive mean between buffers? With the drive capability of the BOSOZ could you drive a passive filter for the midrange and buffer the other high and lowpass filters. So many possibilities and the circuit hasnt even been built yet.



I have to agree with what an earlier post said. That we try to keep the signal path as short as possible then we add all this circuitry for an active x-over. A simple passive for the right midrange seems like a good compromise.

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Old 9th January 2004, 12:52 AM   #90
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Hi,

Quote:
A simple passive for the right midrange seems like a good compromise.
I'd second that....

Have you considered multi-amping the mids/highs passively?

Cheers,
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