Tuesday, September 20, 2016

Clocks, clocks

We can tell the Pioneer PD-75 and PD-95 clocks are about the same by reading the modification instructions by Octave who makes clock upgrades.  The replacement instructions regarding the parts changes are identical.

So the PD-75 has the same clock circuit as the PD-95.  And BTW it's not the cheapest circuit, it's the step-up circuit.  In the cheapest circuit a crystal is simply connected to the relevant chip with suitable passive parts.  In the step-up circuit, the crystal and passive parts are buffered, in the PD-75/95 by two layers of opamp buffers.  An initial layer which then drives 3 separate buffers to send clocks to different things.

Not to say, there are a bunch of more sophisticated designs than the first step up.

But I think it's clear that these were intended to be in the elite upper category of CD clock performance (there were two categories established by the Red Book).  So we could expect perhaps jitter at least to be less than 300pS, allegedly 1/30 or less of what would be audible, or less.

The PD-95 might benefit even in jitter performance simply by having better power supply.  That has huge effect on simple oscillator clocks.  Good clocks are designed to be immune, though nothing is ever entirely immune from influence, within the same electronics.

Meanwhile it's bugging me that nobody talks about simply replacing the Sonos Connect (formerly known as Zoneplayer ZP80 and ZP90) clock the way one might do for a CD player.  (BTW, in some accounts replacing the clock is essentially the only thing that ultimately determines player-added jitter at the output terminals.  The clock ultimately controls the clocking out of bits, and it doesn't have to vary that rate one iota because servos earlier in the system keep buffers filled with enough data.  If not, there's a skip, which rarely happens anymore with good players and discs.  In other circles, everything counts.)  Instead, it seems the major recommended replacement now adds a whole circuit board which does reclocking on the output.  I would rather avoid reclocking because it only just smoothing the underlying jitter.  It's not really eliminating variation because it can't, it's shifting it somewhat to a lower frequency, so jitter becomes very low frequency wow.  And not only reclocking, but ASRC to 96kHz, or your frequency of choice.  That might actually be good for me, but I think I'd rather do analog resampling than ASRC.  And I've had a longstanding bias against ASRC as simply "buring the jitter in the data, where it cannot be removed".  So why not just replace the clock.  The blurbs all say "multiple lousy clocks."  I'd like to see that for myself, I still think fixing the actual clock is better than any band-aid ASRC.  If it's true there are multiple clocks, why not replace the one that counts most, or all of them, or something?

I suspect that the difference between the existing PD-75 clock and something better would not be by anyone audible in ABX DBT.  But of course, I gotta have the best clock anyway, just to be absolutely sure.

I've asked Kingwa if he still makes his Audio G_D jclock.

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