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Old 13th April 2011, 02:12 AM   #1
ronpod is offline ronpod  United States
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Default Legato output impedance

Hi Russ,

My B2-Legato feeds an active crossover as the following stage. The high frequency selving filter in the active crossover is sensitive to the output impedance of the Legato and needs to be adjusted as appropriate. Can you provide the output impedance of the Legato 2.0 and the upcoming Legato 3.1 so that I can make the adjustment to the active crossover?

Many thanks, Ron.

Last edited by ronpod; 13th April 2011 at 02:15 AM.
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Old 13th April 2011, 06:21 AM   #2
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Hi,
if you make a research it has been talking many times about this question, here or in the support forum of TPA.

GM
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Old 13th April 2011, 07:58 AM   #3
needsp is offline needsp  United Kingdom
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Hi Ron

~150R. It's equal to the output impedance of the circuitry- which is high- in parallel with the I/V resistor, which is 150R

hope this helps

Paul
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Old 13th April 2011, 12:42 PM   #4
ronpod is offline ronpod  United States
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Thanks for the replies GM and Paul,

The output impedance is useful immediately for the Legato 2.0 but once the L3.1 is released it will replace the L2.0 in my system. So I was hoping for some assistance from Russ to ensure my system planning will anticipate the new Legato. I would likely use the SE out.

Thanks, Ron.
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Old 13th April 2011, 06:41 PM   #5
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Why not use a buffer before the shelving filter? That way it will work with whatever is before it.
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Old 13th April 2011, 06:57 PM   #6
avr300 is offline avr300  Denmark
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Ron, are you here talking balanced or SE output ?

Last edited by avr300; 13th April 2011 at 07:04 PM.
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Old 13th April 2011, 07:26 PM   #7
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Quote:
Originally Posted by avr300 View Post
Ron, are you here talking balanced or SE output ?
Quote:
Originally Posted by ronpod View Post
Thanks for the replies GM and Paul,

The output impedance is useful immediately for the Legato 2.0 but once the L3.1 is released it will replace the L2.0 in my system. So I was hoping for some assistance from Russ to ensure my system planning will anticipate the new Legato. I would likely use the SE out.

Thanks, Ron.
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Old 13th April 2011, 08:18 PM   #8
avr300 is offline avr300  Denmark
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I'm blind. Sorry.

The SE output impedance is much less, it's the output impedance of the OPAMP and in the v.3 the output diamond buffer.
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Old 13th April 2011, 10:25 PM   #9
ronpod is offline ronpod  United States
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Quote:
Originally Posted by 5th element View Post
Why not use a buffer before the shelving filter? That way it will work with whatever is before it.
Yes, a good suggestion. But isn't the version 3 of Legato designed in the spirit of less is more? Fewer components mean less opportunity for noise and distortion to intercede. Certain the law of diminishing returns begins to apply at some point and less is then less.
The ASP that encompasses the active crossover has plenty of circuitry including opamps but I would like to keep the signal feeding it as clean as possible.
Wouldn't a buffer that maintains phase require two stages?

If the output impedance of Legato 3.1 (SE) is less then 200 ohms then I do not have to do anything to my ASP circuit; all will be right in my audio world.

Thanks, Ron.
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Old 13th April 2011, 10:36 PM   #10
ronpod is offline ronpod  United States
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Quote:
Originally Posted by avr300 View Post
The SE output impedance is much less, it's the output impedance of the OPAMP and in the v.3 the output diamond buffer.
Do you think that the opamp and diamond buffer would provide an output impedance less then 200 ohms?

Thanks, Ron.
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