PCM1794-->Resistor I/V-->LL1571...

[Ryssen]

I ordered a PCM1794 chip and a 28pin adapter to use in this DAC http://www.diyaudio.com/forums/digital-line-level/137976-experience-diy-dac.html
and I will use a resistor as I/V converter,and after that LL1571.
I have googled the net for examples of the resistor I/V,and I found 2 different topologies.First this one that uses resistors from the output to ground.

And this one that uses a resistor between the balanced output.

Passive output

Wich one to use?

 

[Ryssen]

And how do I calculate a LP filter and wich cutoff frekvency should it be?

 

[analog_sa]

The two topologies are the same.

 

[grael]

The two topologies are about the same because on the passive output from the Rakk dac, they use "center tap" to ground, so the resistor across the secondary is reflected on the primary as "resistors to ground".

You want to use LL1571 as 1:3.5 to lower the resistor presented to the chip output?
Because you can't wire it like that with a center tap... Only when used as 1:1.75

In your position, i'd use resistor to ground on the primary, then LL1571 as 1:3.5

 

[Ryssen]

Yes,they both put a load on the DAC´s output..
But as the LL1571 doesn´t have a center tap connected as 1:3,5 I´ll have to use the 4 resistors from the DAC´s output to ground.
http://www.lundahl.se/pdfs/datash/1571.pdf

But how about the filter at output,or should it be on the secondary?
I don´t wanna set my F5 amp into oschillation...

Edit:grael posted before me.

 

[grael]

I don't know anything about LPF on the output...

The rakk dac works without it, so does my pcm1798 with LL1636.
( http://www.diyaudio.com/forums/digi...new-small-diy-gigawork-dac-5.html#post2201697 )

You could try without first.

edit : we are writing at the same time!
I'd say :

DAC + ----- R--------R----- DAC -
                 |                   
                 |
               Ground

Then Dac+ and Dac- on the primary

With four resistors R = 135 Ohms, you get the same behaviour as the Rakk Dac (load on the dac chip is a bit higher than Rakk dac because your step up is a bit lower)

 

[grael]

R=120 Ohm would do the trick, to keep with standard resistor values

 

[Ryssen]

Yes,I will try without it,but if anyone has any suggestions,they are welcome..

 

[Ryssen]

Yes,at the same time!The above I wrote is about the filter.

I will try with 120 ohms load on the DAC.

 

[hollowman]

That's the ezdac schema you posted. Not a fan of that "design": why include upsampling (a mixed-result, controversial approach at best, IMO) but compromise on much more important I/V with a freakin' R-only I/V "topology"?

 

[Ryssen]

but compromise on much more important I/V with a freakin' R-only I/V "topology"?

I´m thinking "KIS"keep it simple,I don´t wan´t an opamp or a transistor between the DAC and trafo..

 

[Ciu]

Ryssen !

Are you sure PCM1794 is "pin compatible" with CS4398 (even with an adapter)?

R.C.

 

[Ryssen]

I ordered from mr snow468@gmail.com on ebay who sells the DAC boards.
I ordered 1 module with PCM1798 that guys in the "experience" thread have used on that board(slightly modded)as he didnt have a ready made module with PCM1794,I ordered an empty module and got a PCM1794 else where on ebay to solder on the module.I asume that the empty module is the same as the one with PCM1798 (that is pincompitable with PCM1794),but I will check the modules when I get them.