Legato output impedance

[ronpod]

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.

 

[gianmaria]

Hi,
if you make a research it has been talking many times about this question, here or in the support forum of TPA.

GM

 

[needsp]

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

 

[ronpod]

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.

 

[5th element]

Why not use a buffer before the shelving filter? That way it will work with whatever is before it.

 

[avr300]

Ron, are you here talking balanced or SE output ?

 

[merlin el mago]

Ron, are you here talking balanced or SE output ?

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.

 

[avr300]

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.

 

[ronpod]

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.

 

[ronpod]

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.

 

[needsp]

Hi Ron

The output impedance of the opamp and diamond buffer will, I'm quite sure, be very low- much, much less than 200 ohms.

Paul

 

[natzev_i]

Ron, I am quoting here Russ about Legato 3.1 output impedance and abilities:

Less than half an ohm(actually much less).

You shouldn't need anything after the Legato 3/3.1 when used with Buf II and Volumite. Just a power amp.

Hope this helps.
Ivo

 

[ronpod]

Paul - Thanks!

Ivo - "much less" than half an ohm? Can this be?

 

[avr300]

Do you think that the opamp and diamond buffer would provide an output impedance less then 200 ohms?

Thanks, Ron.

Yes, much less. As written, less than 1 ohm.

 

[Russ White]

Yes SE output impedance of the Legato 3.1 with buffer in the audio band is basically the DCR of the output choke. Which is very tiny.

Less than half an ohm(actually much less).

Interestingly the quote before I was actually talking about balanced input impedance. Which is also incredibly low. That is a key feature, and really important to getting the most out of the DAC.

The same low impedance is certainly true of the SE output impedance as well.

Cheers!
Russ1

 

[natzev_i]

Russ, please accept my apologies if I quoted you incorrectly - my mistake!
Ivo

 

[Russ White]

Russ, please accept my apologies if I quoted you incorrectly - my mistake!
Ivo

No worries.

 

[ronpod]

Thanks for helping me understand the L3.1 specs better! So with extremely low input impedance and very low output impedance then the audiophile juice should freely leak out! The L3 will be a very nice addition to the DAC "box."