Legato 3 - Look ma! No caps!

[regiregi22]

Thanks for the inputs, Brian and Russ!

 

[glt]

Filtering...

Hi Russ,

Is L3 filtering designed with 6-bit quantizer in mind (more aggressive) or does it not matter?

 

[Russ White]

Does not really matter. The cutoff frequency is pretty high.

 

[natzev_i]

The buffer and the op-amp are one loop. You cannot really isolate them with removing the buffer from the equation. As I have said multiple times - if you have the buffer, it is only ever a *good* thing. If you don't want to use the buffer order the version with out it. Simple as that.

Russ, I already received but haven't assembled the buffered L3.1 version yet.
Now, if by some reason I decide to not use the buffer I need to order the non-buffered PCB only and populate it instead?
May be it's my misunderstanding but I always thought that the buffer can be used or easily bypassed, if desired.
Could you please post the non-buffered schematics also.
Thanks,
Ivo

 

[leif christensen]

just don´t mount the buffer parts
pretend you never got them in the first place
best
Leif
norway

 

[Russ White]

There is no case where I would suggest the un-buffered version except to save cost. Build it and be happy.

If you don't want the buffer you would need to remove it.

The schematic is the same for the non-buffered version, just without the buffer and add the two jumpers.

 

[BrianDonegan]

I am pre-mounting the buffers, as it can be difficult to properly solder them with an iron (thermal pad to PCB).

 

[leif christensen]

I run unbuffered balanced into a S&B TVC
what am I missing?
best
Leif

 

[BrianDonegan]

There is no buffer for the balanced outputs, only the SE out.

 

[leif christensen]

good then!
thxs
any news on Trident availability?
best
Leif

 

[natzev_i]

Russ, Brian and leifchristensen ,
Thank you for the quick response but I am confused a bit.
Russ, you said:
"The buffer and the op-amp are one loop. You cannot really isolate them with removing the buffer from the equation"
am I missing something, please?

 

[BrianDonegan]

If the Buffer is on the board, you must use it. If it is not there, it is possible to use just the opamp by added jumpers at positions J5 and J6.

 

[leif christensen]

that´s likely meant to be on the single ended output only
best
Leif

 

[Russ White]

With should be without. just a typo.

The short of it is, if you don't want the buffer you have to omit it.

Simple as that.

But if you already have it, it would be silly not to use it. Here is why, it isolates the output stage of the op-amp from the load, letting it do its job better. It does not even really matter what kind of load it is.

 

[natzev_i]

It's perfectly clear to me now - thank you very much!
I wanted to build an unity gain active discrete pre-amp B4 buffer (similar to PAS B1) to put between Buff II and my power amp.
Now with the Legato's buffer I suppose I will not need it?
Cheers

 

[Russ White]

No you will not need it, and even better, because the buffer is in the feedback loop distortion will be reduced.

 

[BrianDonegan]

No, not really, but you do still have a unity gain active buffer, just not discrete as all the transistors are mounted in the same package. You get the advantages of tight thermal coupling and better matching.

 

[natzev_i]

So, it's a win-win situation!
Thank you guys for making my life easier!

 

[Jean-Charles]

I have the Legato 3.1 up and running with the buffer in. No need to worry guys, it is awsome. Just listen to it.

 

[oneday]

The capless balanced output of the Legato 3 is of interest to me as I've recently got a amp with balanced inputs. However, as I haven't long built a kit DAC based on a DSD-1796 chip, I'm wondering whether the Lagato could used with this DAC, albeit with some changes to accommodate a balanced output current (from the datasheet - Output current Full scale (0 dB) 4 mA p-p; Center current At BPZ –3.5 mA) that I'm guessing will be somewhat lower than that of the ESS9018 DAC.

cheers..oneday