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Old 28th April 2009, 09:56 PM   #1
taotao is offline taotao  Germany
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Join Date: Oct 2004
Location: Cologne
Default PCM63 stepping up

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/showt...7#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
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Old 29th April 2009, 07:49 AM   #2
Zoran is offline Zoran  Serbia
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Join Date: Jan 2004
Location: Belgrade
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...
*
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Old 29th April 2009, 08:02 AM   #3
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Olaf,
Have a look here:
http://www.audiodesignguide.com/cdplayer/dac3.html

Click the image to open in full size.
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Thanx!
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Old 29th April 2009, 11:32 AM   #4
taotao is offline taotao  Germany
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Join Date: Oct 2004
Location: Cologne
Yes, thank you both.

I decided to take a different approach with tubes.

Have fun
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