Originally Posted by rsbeck
I think everyone agrees that an outboard DAC can improve the sound of a Sonos ZP-80 or ZP-90. Mods are a little more controversial.
I am also wondering about modifications like Cullen or Empirical Audio's Pace Car.
There seems to be a few main issues addressed by either or both;
2) Power Supply
There have been many unsubstantiated claims that the Sonos units introduce high emounts of jitter. To my understanding, Stereophile sent the unit out to be tested and the results showed that the Sonos units actually exhibit very low jitter.
Personally, I am not clear on whether the jitter reduction claimed by the modders is really lower than an unmodified Sonos unit.
I believe both modifications address the Power Supply, but a study of the advertising reveals very little before and after info that isn't purely anecdotal.
I am also not sure how upsampling would improve the signal. My understanding is that it is generally believed by audiophiles -- I include myself here -- want to keep the original signal as pure and unprocessed as possible, so I am not sure what upsampling would add and -- again -- a study of the advertising reveals very little in the way of facts; no white papers, nothing.
A search of the web reveals very few actual testimonials from owners using these mods, so they do not seem to be in widespread use.
A good DAC can make all the difference.
The problem with the CD standard is that sampling is at 44.1kHz which
means sampling artifacts appear at 22.05kHz. CD players must implement
a very sharp cutoff filter such that the output is about 100dB below full scale
@22.05 kHz . The worst case is the audio is fullscale at 20kHz and
the filter must ensure the aliasing noise is 100dB below this @22.05kHz.
The task is split between the digital filter before the DAC and the analog
filter after. In the digital domain the audio data is a stream of numbers
and the filter is a long mathematical equation with lots of coefficients.
These are grouped into filter taps and each tap is a processing stage.
The steeper the filter the more taps are required and it can get
One way to reduce the steepness of the filter is to move the sampling
artifacts out to a higher frequency significantly above 20kHz. The
cheapest way is to resample the data stream. In the case of 96kHz
this moves the aliasing artifacts to 48kHz and allows a very significant
reduction of the slope (100db over 2.2kHz vs 100db over 28kHz, about
1 order of magnitude)
If we were to resample, the steepness and hence complexity of the
digital filter downstream is reduced as there is less processing to do.
However this has to be traded off against the complexity of implementing the
So upsampling is another method to dealing with the problem of the
low sampling frequency specified by the CD standard.
As to whether upsampling will bring additional sonic benefits, that
depends on the downstream DAC's ability to perform the filtering
at 44.1kHz with a minimal of artifacts. If it does a good
job upsampling is not needed.
The newer DACs that can operate at higher sampling rates typically
optimize their digital filters for the higher sample rates. In addition
the Delta-Sigma conversion method is quite commonly used
It works better (lowerinband noise) if the converter is clocked at
a higher frequency, and this frequency is proportional to
the sampling rate.
My ZP90 is connected to an Onkyo 875. It uses the TI/BB PCM1796,
a great DAC if a high sample rate is used.
This gives barely passable 44.1kHz performance. I use a variant
of the Monarchy DIP which resamples to 96kHz, the performance
changes with it.
I can get equivalent performance with a Goldmund DA96 without
resampling. This DAC has custom digital and analog filters