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Legato Tweakers Thread...

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If you are only using the SE output it is already buffered so you can very safely omit the balanced output buffer, and I would recommend that.

Cheers!
Russ

Is there an advantage to omitting the balanced output buffer?
I will be using mostly SE, but I also have an amp with balanced in w/input impedance of 2K only, so for that amp I would want the buffer.
It would be easier to install the buffer in the primary build than add it later, but if it adversely effects the SE performance, I won't install it until I want to try it.
It seems to me that it shouldn't be an issue, but advice is welcome. Thanks!
 
Thanks Russ,

There are adaptors like this:
Dual to Mono Op amp OPA627BP OPA627 replace NE5532 - eBay (item 350409857543 end time Dec-01-10 23:54:36 PST)

Since I use the SE output in dual mono 2 Legato, my question is if there will be any improvment by changing the opamp by a better one.

Thanks again

Theo: The OE opamp is very good. The use of the word "better" above is not really relevant. Certainly you will get different sound by trying different opamps, but not necessarily "better". The only way to know would be to try it. You can research which opamps might be pin compatible on the various opamp threads here at DIYaudio.
Of course, IMO, avoiding the opamp alltogether will result in "better" sound.
 
Theo: The OE opamp is very good. The use of the word "better" above is not really relevant. Certainly you will get different sound by trying different opamps, but not necessarily "better". The only way to know would be to try it. You can research which opamps might be pin compatible on the various opamp threads here at DIYaudio.
Of course, IMO, avoiding the opamp alltogether will result in "better" sound.

Thanks Barrows,

But how we can avoid opamps in dual mono configuration ?
 
I would like to know how to mod the Legato to use with single ended pcm1704 DAC?

Merlin, as its a current output DAC can you take the left and right outputs from the DAC chip and connect them to the Legato's normal inputs. Only use the positive and negative connectors on the Legato, don't bother with the GND connection. If the gain is low you will have to tweak some resistor values.

Would this work or am I missing something?
 
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Merlin, as its a current output DAC can you take the left and right outputs from the DAC chip and connect them to the Legato's normal inputs. Only use the positive and negative connectors on the Legato, don't bother with the GND connection. If the gain is low you will have to tweak some resistor values.

Would this work or am I missing something?

No that would not work.

You could use Just +in and GND, or Just -IN and GND on each side, and then connect the unused input to GND. But this would not yield great results.

You should definitely connect GND.

Simply put the Legato is designed for balanced output DACs. You might be better off with a single ended I/V stage.
 
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Thanks for help, I searched a SE discrete I/V but don't finded nothing, what about the filter, don't need to be modified?

You bet, you will need to do a lot of modification. You will want to change the I/V resistor and the CCS to better match the chip. You will need to look at the datasheet to make some choices there. The filter cap will depend on the I/V resistor.
 
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The datasheet don't tell nothing of the I/V resistor because said:

"The I/V converter, and the DAC post filter. Selection of an appropriate op amp for the I/V converter is critical for obtaining optimum dynamic performance from the PCM1704. The OPA627 is recommended for this application. Op amps with similar characteristics and faster settling times may also be used. The suggested DAC post filter is a second-order lowpass active filter, using the multiple feedback (MFB) circuit technique. The OPA2134 is an excellent choice for the op amp in this circuit, since it is designed for high performance audio applications. The post filter is used to reconstruct and band limit the DAC output signal"

If I remember well I read that PCM1704 I/V pasive resistor is 100 ohms, please could you help me how can be do?
 
You need to change both R1-4 and R20,21,23,24 to change the gain. I believe Russ notes the ideal ratio between the upper resistors and lower is 2.2.
I got 1.9 volt output with the following combination:
R1-4: 180R
R20,21,23,24: 390R

Barrows,

do you have an idea of the proper values for the Legato 2.0 ??. The resistors in the new version have different values and I am not able to figure out the right values in order to get 2.0 volts aprox.

Any help would be very much appreciated.

Cheers,
Pepe
 
I believe...

that the Legato v 2 is the same, except that the lower resitors have been doubled up (in parallel).
My understanding would lead me to say 180 for R1-4, and then 390*2 for the eight others (as they are 2 resistors acting in parallel).
So 180 and 780 would result in around 1.9 V out.
Hopefully if I have this wrong someone will correct me!
 
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