If you look at the datasheet for the dac chip in the squeezebox
(pcm1748), you'll see that it is spec'd to drive a 5k load.  With my
modified squeezebox where I take the output directly from the pcm1748,
bypassing the output stage, I find that the sound is much better IF you
are driving a high enough impedance.  For example driving a tube preamp
with 100K input impedance, it sounds great and is equal to or better
than using an outboard DAC.  If you take the preamp out of the chain
and drive the amp directly, the sound actually is worse.  The reason
for this is that the amp has ~10K input impedance.  
If you drive a lower impedance such as 10K then you are getting close
to the drive capability of the pcm1748 and it sounds less good -
meaning that it still sounds good but maybe no longer better than the
external dac which has a very good output buffer.  As always, matching
of components is the key to getting the best sound.

---Gary


-- 
GaryB
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