PCM63 stepping up

[taotao]

Hello,

can somebody tell me, if the following is right?

I like to connect pcm63 with LL1636 (stepup-ratio 1:20)
By viewing this: http://www.dddac.de/pcm63/DAC_I-V_Resistor.htm
and reading the diyaudio-thread: http://www.diyaudio.com/forums/showthread.php?postid=1567227#post1567227, it becomes clear, that the Resistance seen by the dac should not exceed 100 ohms, to avoid distortion. It seems a good value is arround 10 ohms.

If I put a resistance of 20k in parallel to the secondaries, the dac "sees" 100 ohms (20k/200), right?

But my volume pot has also 10k, so the dac is loaded by 42 ohms (8k3/200).

This value seems OK.
But now, my dac has an output impedance of 20k. How critical is the cable to my preamp? Can it be standard coax-type?

Or better put the transfomer in the preamp?

Thanks for input/ideas

Olaf

 

[Zoran]

It is also depends of primary dc resistance of the tr.
if it is low you will close to put in short I outs...
and if You put transformer directly at the I output
You will have some cd current flow through the primary winding
causing probably distorsion in core by cd saturation?
*
the value of 10 ohms fro passive R IV, could be really low
and damage the chip, so take care
stick about 100ohms for the first start...
*

 

[bequerel]

Olaf,
Have a look here:
http://www.audiodesignguide.com/cdplayer/dac3.html

 

[taotao]

Yes, thank you both.

I decided to take a different approach with tubes.

Have fun