baardbaard;517162 Wrote: > Lets look into some measurements with audible effect from John > Atkinson: > > The Squeezebox's frequency response (fig.1) showed a slight > shelving-down at low frequencies that might just be audible given the > wide range covered. (this has nothing to do with SMPS). > > Now to something that may be effected by the minuscule wall-wart.: > > Fig.2 shows the spectrum of the Squeezebox's analog output analyzed > with a swept 1/3-octave bandpass filter while it decoded dithered data > representing a 1kHz tone at 90dBFS. The traces are free from both > power-supply and harmonic-distortion spuriae and peak at 90dBFS, > suggesting good DAC linearity. The right-channel trace has some energy > peaks centered on 9kHz and 18kHz, but these are low in level. Both > channels also have a small energy peak evident at 30Hz, and the overall > noise floor is 1020dB higher in the midrange and bass than with the > best 16-bit playback devices. > > Summarize: > the Squeezebox measures very well. Its noise floor is higher than that > of good CD players. Great. The noise on the right-channel is likely to be related to the VFD, which is known to affect one channel more than the other. Some people can actually hear the VFD noise breaking through (with their amps at full blast).
If I am interpreting JA's graphs correctly, the average noise floor seems to be sitting between -105 to -110dB. I'm not sure how that equates to "1020dB higher in the midrange and bass than with the best 16-bit playback devices". However, -100dB is quiet. You would have to have lots of gain and very sensitive speakers or very powerful amplifiers to be able to hear anything at that level. If JA was to repeat his tests with a different PSU... My tests show that the noise floor of the Touch is substantially below that of the SB3. In part this is explained by the absence of the VFD, but also by other circuit changes. Direct null testing of the stock PSU vs a quiet linear and even with batteries on the SB3 show no differences above -90dB. So it seems that the noise floor performance is being set by the SB3 itself not its supply. I have been unable to measure any performance improvement simply by changing the PSU. I can't hear one either. I should point out that I did swap my SMPS for a linear some years ago but have since swapped it back as the SMPS uses a lot less electricity and I can't hear or measure any benefit. With the Touch we are talking about a much lower internal noise floor (-20dB from memory) to begin with - and I still can't hear or measure any change in audio quality with different PSU's. -- Phil Leigh You want to see the signal path BEFORE it gets onto a CD/vinyl...it ain't what you'd call minimal... SB Touch Beta (wired) - TACT 2.2X (Linear PSU) + Good Vibrations S/W - MF Triplethreat(Audiocom full mods) - Linn 5103 - Aktiv 5.1 system (6x LK140's, ESPEK/TRIKAN/KATAN/SEIZMIK 10.5), Townsend Supertweeters, Blue Jeans Digital,Kimber Speaker & Chord Interconnect cables Kitchen Boom, Outdoors: SB Radio ------------------------------------------------------------------------ Phil Leigh's Profile: http://forums.slimdevices.com/member.php?userid=85 View this thread: http://forums.slimdevices.com/showthread.php?t=75092
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