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Old 18th July 2014, 06:01 PM   #1
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Default Bi-AMP with OB - no need for LLXO

Hi, I am using a line level active cross over (XM1) to biamp between:
2A3 amp -> Fostex 208ez open baffle
AND
SS amp -> Eminence woofers (<150hz).

Could I get rid of the cross over in the line to improve the sound? The open baffle doesn't need a high pass so I am thinking I could tap into the speaker output with a low pass filter to the ss amp (as in the attached pdf). That way everything <150hz doesn't have to go through the XO opamps. The resistor values are approximate. Does anyone have experience with this approach?
Henry
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File Type: pdf speaker level biamping.pdf (22.8 KB, 24 views)
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Old 18th July 2014, 07:18 PM   #2
chrisb is offline chrisb  Canada
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I'd be inclined to disagree with you on "no need" for HP for the Fostex - I think you find it is much more comfortable operating with the reduced excursion - particularly in an OB

you could get away with a very simple passive line level XO - if there's room for an extra pair of RCAs on the 2A3 amp you could literally build it into the amp, and tap the isolated outputs to the woofer amp in the same chassis
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Last edited by chrisb; 18th July 2014 at 07:24 PM.
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Old 18th July 2014, 10:05 PM   #3
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Hi Chris, thanks, I didn't think about the benefits of XO for the Fostex. The 2A3 has plenty of room so I will try your idea. How simple a XO can I use? Could I get away with one cap?
Henry
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Old 18th July 2014, 11:32 PM   #4
sreten is offline sreten  United Kingdom
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Hi,

You can add a simple high pass cap to the 2A3 input
and then add a cap||R in series with the 100R resistor
to create an inverse filter to drive the subwoofer,
which still needs some form of low pass filter.

rgds, sreten.
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Old 19th July 2014, 01:30 AM   #5
chrisb is offline chrisb  Canada
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Read this primer on PLLXO, it includes an excel worksheet for calculating component values

TLS.org | Passive Line-Level Crossover

Yes, if you factor in amp's input impedance in the calculus, you can get away with a single cap, which allows you to get spendy if you like


If you already have a conventional SS power / integrated amp for woofers, you'll likely need the LP XO as shown, and volume controls on each for balancing relative levels never hurts
If not, I rather prefer something like this guy to plate amps:

Dayton Audio APA150 150W Power Amplifier
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Last edited by chrisb; 19th July 2014 at 01:33 AM.
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