Legato 3 - Look ma! No caps!

[alazira]

I tried F5X( Euvl), but does not work without capacitors

I do not see any use of ground in the schematic. I wonder why it didn't work without caps?

 

[kotani]

I'm running dual mono Legato III's with a pair of Pass Aleph 0, balanced. It may be a similar design with the First Watt's.

The setup sound great, with no problem with DC. That's using the SE outputs though, as they are in dual mono. I remember Brian or Russ stating somewhere that you are only able to dial out common mode DC on S.E. outputs and not the Balanced outputs, but I could be wrong. I'll see if I can find that post somewhere.

Has anyone tried the Legato 3.1's balanced output in to a Nelson Pass First Watt F1 or F1-J current output amplifier? Can they handle the DC or would I still need coupling caps?

I am intrigued by the idea of a class A lightly damped power amp for my Lowther open baffle speakers. I haven't even received my B3 yet and I'm starting to think about the 'next' project....

 

[zkdaz]

Thanks kotani, you are right though, a dual mono setup uses the balsie's to create it's balanced output so you will not have common mode DC going to your Aleph.

I am starting to think of leaving the legato for use with the sympatico amps only and using a circuit based on Nelsons Zen I-V converter straight off the Buffalo to feed the First Watt F1J amp. No feedback and only two gain stages between DAC and speakers.

Russ; What is the output power and impedance per channel of the B3 in current mode? I presume it is the same as the B2 but I can't see it in the manual or specs.

 

[AndriyOL]

Interesting why in Legato's schematic there are 2 IC1 (LM4562), however in BOM and on a picture only one or I haven't seen the second?
What will be the best replacement for that IC from subjective point of view?
What I considered worth to be tried only AD797 or LME49990.

 

[BrianDonegan]

Interesting why in Legato's schematic there are 2 IC1 (LM4562), however in BOM and on a picture only one or I haven't seen the second?
What will be the best replacement for that IC from subjective point of view?
What I considered worth to be tried only AD797 or LME49990.

It's a dual opamp. You are seeing the two subsections in the schematic.

 

[AndriyOL]

It's a dual opamp. You are seeing the two subsections in the schematic.

Thanks Brian! I missed it. What a shame..

 

[vitalica]

I do not see any use of ground in the schematic. I wonder why it didn't work without caps?

I apologize, I was on vacation
I do not know why not work without caps ...
The balanced output we now 33/16vBG (N) and F5X work.
But without them, no.
But I wanted very much not to put capacitors ..

 

[alazira]

I apologize, I was on vacation
I do not know why not work without caps ...
The balanced output we now 33/16vBG (N) and F5X work.
But without them, no.
But I wanted very much not to put capacitors ..

Hi Vitalica,
What is the balanced ground input connected to?

 

[needsp]

Hi Russ

You changed the values of C19-22 and C1-4 when you designed Legato 3, from 1 to 2n2 and 15n to 2n2 respectively in Legatos 1 and 2.

Was the change to C19-22 to optimise the circuit following the adoption of TP0604 mosfets?

I'm still using an earlier Legato, modified to use TP0604, and 1n caps. Would it be worthwhile to change these to 2n2?

For what it's worth, I use 1n SMD Panasonic ECHU caps here, mounted as close to R5-8 as possible (also 3n3 ECHU for C1-4)

Thanks

Paul

 

[Russ White]

The change was mostly driven from listening to the thing for a year or two, but yes the new FETs did influence my decission.

 

[needsp]

Hi Russ

Sounds as if it would be worthwhile me changing to 2n2 then- thanks!

 

[zhai]

Hi all

I'm about to build a Buffalo DAC, and I have some questions.

I would like to use the DAC to feed both a power amp and headphones directly, using the Legato, so what would be the best way to accomplish this? Should I just hook the s/e part up to a headphone out, and if I do this, will the signal pass to both headphones and power amp (connected with balanced signal) at the same time?

Should I, instead, find some way of switching between the activation of these two signals, so that I can turn a knob on the front of the DAC?

I guess my level is about intermediate, as I have built only a few pieces of sound equipment before - DDDAC, TPA preamp and UcD power amp.

 

[avr300]

Should I just hook the s/e part up to a headphone out, and if I do this, will the signal pass to both headphones and power amp (connected with balanced signal) at the same time?

That's the way I do it and it works flawlessly.

 

[LeonvB]

Should I just hook the s/e part up to a headphone out, and if I do this, will the signal pass to both headphones and power amp (connected with balanced signal) at the same time?

Correct. The SE out of the Legato should be powerful enough to drive most headphones.

 

[Erlend Sæterdal]

Anyone know how low impedance its possible to run on the balanced output ?

 

[MWL168]

increase SE buffer output

Hi Russ:

I can not get enough volume with my Audaze LCD 2 headphone which is rather inefficient. What can I do to increase the gain of IC1?

Thanks!

 

[MWL168]

Legato 3.1 SE output gain

Hi Russ:

Based on what was stated in the Ventus headphone amp manual; I assume the gain of IC1 is R21/R17 = R22/R18 = R23/R19 = R24/R20. Is this correct?

I also have the following questions:

1. Is it better to lower the value of the resistors determining the input impedance to IC1 (R17 - R20) or raise the value of the feedback resistors (R21 - R24)?

2. If I choose to lower the value of R17 - R20, is it necessary to make the R33 - R36 the same value?

3. Do you have recommendation what resistance range I should use? Currently, using iTune on my Mac BookPro laptop as source, I have to be in the last 1/4 of adjustable range of the Volumite to get enough volume - this with the iTune's volume maxed out.

Thanks!

 

[Russ White]

For best results simply adjust R21-24. Try doubling them for now.

 

[MWL168]

Thanks Russ!

I don't have 10K resistors handy so instead I put 7.5K Caddock MK132 0.1% in R21 - R24. I still have to turn the Volumite pass 2/3 of the way but I am now getting enough volume for my headphones.

Unless you have concerns I'll just leave the Legato the way it is now.

Thanks again for your help!

 

[Erlend Sæterdal]

Legato 3 with discret opamp

Anybody know if it is possible to change the LME 49720 to a Dexa discret opamp ( the Dexa have Bipolar input cicuit ) ? I am asking because of the common feedback circuit.