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My build blog for my active 3 ways.
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The B1 active XO's

Posted 23rd November 2009 at 07:26 PM by relder

Tony asked about the B1 active XO's. There's really not much to say. Any active filter that uses an opamp as a buffer (I.e. where output is directly tied to the '-' input) AND a cap blocks DC from the output to the feedback loop should be able to use a B1 like buffer. The circuits in sections 1, 2, 3 and 7 of SL's filter page all qualify, but the rest may be sketchy in my mind since the B1 can have some DC offset.

Attached is a rough drawing I scribbled last night for my own benefit, so it ain't pretty. An input buffer is something I'm still debating needing or not, but I'm leaving some room for it.

I'm going to let Soundeasy help me define the values, but the drivers are pretty well behaved in their desired bandwidth such that nearly textbook filters can be used.

I don't have enough JFETs of any one type for everything, so I'm going to have to mix types, probably LSK170s for the woofer and Toshi 2SK170s for the mid/tweet.

Rob
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  1. Old Comment
    wintermute's Avatar
    Now that is what I was interested in! I see from your schematic that you have put in feedback.... also cascading two filters, I will be very interested to hear what you think of this. I'd been thinking I'd either have to have a purely passive filter before the B1 (ie not have the B1 be part of the filter) or use opamp based filters between B1's. (designing my own circuits is a bit beyond me unless it is something as simple as a transistor set up as a switch )

    The other issue I have been grappling with was whether I needed to have all the B1's on the same board using the same star ground to avoid any earth loops.

    Tony.
    permalink
    Posted 24th November 2009 at 08:11 PM by wintermute wintermute is offline
  2. Old Comment
    relder's Avatar
    Quote:
    Originally Posted by wintermute View Comment
    I see from your schematic that you have put in feedback....
    That's what makes an active filter 'active', feeding back some of the signal to boost/attenuate desired frequencies.
    Quote:
    Originally Posted by wintermute View Comment
    also cascading two filters, I will be very interested to hear what you think of this.
    Apparently I think highly of it ,but we'll see when I get finished with this monster of a project
    Quote:
    Originally Posted by wintermute View Comment
    I'd been thinking I'd either have to have a purely passive filter before the B1 (ie not have the B1 be part of the filter) or use opamp based filters between B1's. (designing my own circuits is a bit beyond me unless it is something as simple as a transistor set up as a switch )
    It remains to be seen if I'll put in a pre-buffer - it all depends on what preamp I'll be driving it with and if it has enough oomph, I'll be going without initially.
    Quote:
    Originally Posted by wintermute View Comment
    The other issue I have been grappling with was whether I needed to have all the B1's on the same board using the same star ground to avoid any earth loops.
    Tony.
    If I were to do this again, I'd put the amps/XO in a single chassis. All these separate custom plate amps @ each speaker cab wasn't my brightest idea.
    permalink
    Posted 25th November 2009 at 03:36 AM by relder relder is offline
 
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