"R" wrote in message

Stewart Pinkerton wrote in
:

On Wed, 15 Dec 2004 22:45:20 GMT, "Rich.Andrews"
wrote:

What I mean by parallel is that the data stream for one channel
feeds 2 dacs at once and the resultant output of the dacs are tied
together. Many of the high end CD players and D-A units use that
circuit topology as it lowers the distortion levels.

Thinking back for a while, I remember the days when doubling up DAC chips
was sorta popular.

There was even a tweak that stacked two DAC chips on top of each other. This
kinda worked because many DAC chhips of the era had high impedance outputs,
so that their outputs were summed at the input to the following stage.

The net effect was that the output voltage was doubled (6 dB), while any
internally generated uncorrelated noise increased by only 3 dB.

However, the effects of running the sucessive stages at twice the signal
voltage were, err *unspecified*.

I never saw any technical tests that quantified the actual results. Of
course we had the usual "sounds better" garbage from the peanut gallery.

You don't mean parallel, you mean a differential pair. Given that
distortion levels with conventional DACs can be 0.001% or less, do
you think this is important?

Of course, the whole approach is rediculous and futile and turned out to
pretty much be yet another passing fancy of tweakdumb.

I don't think i mean a differential pair. Wuld not a differential
pair be 2 dacs fed with the same source but one dac has it's invert
pin asserted?

This would be the better idea (in a land of futile non-thinking) because it
would eliminate such vanishing amounts of even order distortion as there
might be in the analog side of a quality DAC. Internally uncorrelated noise
would also be reduced, such as it might be.

Right now the better DAC chips are among the most precise of all audio
circuits. In production quantities I understand they run about $30. The real
challenge is finding op amps that will accurately deliver their performance
to the output terminals. Furthermore, if you look at the performance of
commodity DAC chips running about $1 or less, they are often as good or
better than the media being played.