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Old 3rd April 2005, 04:42 PM   #1
ThomasS is offline ThomasS  Denmark
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Unhappy PLLXO driven by Sonic impact - HOW?

The main speakers in my system are full range open baffles assisted by an open baffle subwoofer (20-50Hz). The subwoofer is connected via a passive line level x'over (pllxo) to the output of the amp driving the main speakers.

I have just replaced my chip-amp with the Sonic impact T-amp (WITHOUt connecting the pllxo/sub-amp/sub). The output of the T-amp is "floating" (not connected to ground), which means that I can't just connect the pllxo/sub-amp as this will connect one of the outputs of the T-amp directly to ground.. :-(
Is there a simple solution to this "problem"? I was thinking of creating an arteficial ground by connecting this "arteficial ground" to both output terminal via 2 resistors (e.g. 1-200ohm) - the pllxo would the be connected to positive and "arteficial ground" - will this work? Alternatives?
(I'm working on a buffer which will allow pllxo's to be placed before both the T-amp and sub-amp).

Thank,
Thomas
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Old 4th April 2005, 09:52 AM   #2
joensd is offline joensd  Germany
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Quote:
which will allow pllxo's to be placed before both the T-amp and sub-amp).
That is exactly where the PLLXO (by definition) belongs.

If you include all output/input impedances in your calculations you could try it without any buffer.

http://www.t-linespeakers.org/tech/f...ssiveHLxo.html
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Old 4th April 2005, 02:09 PM   #3
ThomasS is offline ThomasS  Denmark
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Pllxo's work's quite well driven from power amps too.. :-)

I need a buffer/pre-amp - otherwise the xo freq will change with the volumen setting (?).

Any suggestions for a solution for the "T-amp problem"?
Thomas
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Old 4th April 2005, 04:25 PM   #4
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Quote:
Originally posted by ThomasS
Pllxo's work's quite well driven from power amps too.. :-)
No, you are still getting it wrong, the output of a power amp is not line level, so the "LL" in "PLLXO" is not there.

So I am even more intrigued, does this mean you have a speaker crossover made up entirely of resistors and capacitors?
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Old 5th April 2005, 10:08 AM   #5
ThomasS is offline ThomasS  Denmark
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"l" is just a less know abbrevaition for "power":
pllxo = passive power level x-over......

It works quite well as the output impedance of the poweramp is low: low imp - > pllxo -> high imp sub amp (like between pre- and power amp). The pllxo is connected to the power amp via a 200ohm resistor.

And yes - a 3rd order consisting of 3 resistors and 3 capacitors - very easy to tailor the response to subwoofer/room - resulting in a flat 20-45Hz response and then a roll-off matching the main speakers.

Draw-backs: high insertion loss (not a real problem) and the need of an extra poweramp (which you would need anyway if you use open baffle subs with chip or T-amps) - so in this particular case there is no real draw-backs
Thomas
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