MDAC First Listen (Part 00101010)
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Purité Audio
Trade: Purite Audio
I thought the PM was the first dac with HDCD , the process was developed by Keith Johnson was it not?
@ Adam what was the hires thing?
Keith
@ Adam what was the hires thing?
Keith
JohnW
pfm member
No we beat Keith at his own game (Keith was just one member of a great team at PM) - the first Pink Triangle HDCD filters used Ceramic "first spin" Silicon at US$100 each (or maybe it was US$500 each). The IC's only worked at 256FS clock as PM had underestimated the power requirements of the PM100's internal ROM section. Luckily a simple metal mask was able to correct the issue - the second spin plastic versions where the officially released parts.
JohnW
pfm member
JohnW, I am trying to PM you...but your account is full
Two spaces freed - I have an new OLED panel sitting besides me, was it for your MDAC?
JohnW
pfm member
Thank you, every payment helps to fund the development
Its takes some effort to engineer even a "simple" design such as the Detox correctly Working on the clock for the Detox and I found a way to improve the FDAC's clock so I'm happy to have this "second pass"....
moosemeat
pfm Member
Very interesting, thanks John.
Interesting...
Wonder how a glass Toslink would perform? Particularly since I have found that an (copper) SPDIF cable is sonically better than a glass TOSLINK between my universal transport and DAC.
JohnW
pfm member
Adam,
Here's an interesting test result showing the Crosstalk / Phase noise modulation between 2 logic gates on the same silicon substrate.
The IC under test is a 74HC04 HEX logic inverters in a single package (only x2 logic gates are used in this test).
12MHz clock inputted into 1 Gate, with its output feed to the spectrum analyzer.
11.9985MHz is feed to a second logic Gate (this signal can be toggled on and off to demonstrate the phase noise modulation between between 2 gates within a single device package). There is no load on the output of this logic gate.
The 74HC04 HEX inverter is the simplest logic gate you can find - in this test only 2 logic gates are operational - imagine the phase noise effect of millions of logic gates in a typical "complex device" such as a USB input device or a integrated DAC IC.
https://dl.dropboxusercontent.com/u/86116171/12MHz Logic gate Isolation.jpg
In the above Spectrograph you can see the the phase noise caused by the second logic gate operating at a slightly different frequency - the expanse of spurie products. The Phase noise induced spurie between the two logic Gates is about -50dBc, it will be worst as the operational Frequency is increased.
At a couple of locations on the Spectrograph I turned off the second input frequency so that the second gate is silent - and you can see the clean portions on the Spectrograph with only the main 12MHz Gate toggling.
The Single Gate operating only...
https://dl.dropboxusercontent.com/u/86116171/Clean 12MHz Logic.jpg
The purpose of this test was to demonstrate how external phase noise can cross domains at the digital level - this is why Memory buffers etc. offer jitter poor isolation unless VERY VERY carefully designed - and not as an integrated solution.
Its also why its important even with an ASync DAC to insure that the USB input is as free of unwanted Phase Noise as possible - hence why I believe that the Detox is a good idea (especially when its clock-locked to the DAC's USB port's clock).
Here's an interesting test result showing the Crosstalk / Phase noise modulation between 2 logic gates on the same silicon substrate.
The IC under test is a 74HC04 HEX logic inverters in a single package (only x2 logic gates are used in this test).
12MHz clock inputted into 1 Gate, with its output feed to the spectrum analyzer.
11.9985MHz is feed to a second logic Gate (this signal can be toggled on and off to demonstrate the phase noise modulation between between 2 gates within a single device package). There is no load on the output of this logic gate.
The 74HC04 HEX inverter is the simplest logic gate you can find - in this test only 2 logic gates are operational - imagine the phase noise effect of millions of logic gates in a typical "complex device" such as a USB input device or a integrated DAC IC.
https://dl.dropboxusercontent.com/u/86116171/12MHz Logic gate Isolation.jpg
In the above Spectrograph you can see the the phase noise caused by the second logic gate operating at a slightly different frequency - the expanse of spurie products. The Phase noise induced spurie between the two logic Gates is about -50dBc, it will be worst as the operational Frequency is increased.
At a couple of locations on the Spectrograph I turned off the second input frequency so that the second gate is silent - and you can see the clean portions on the Spectrograph with only the main 12MHz Gate toggling.
The Single Gate operating only...
https://dl.dropboxusercontent.com/u/86116171/Clean 12MHz Logic.jpg
The purpose of this test was to demonstrate how external phase noise can cross domains at the digital level - this is why Memory buffers etc. offer jitter poor isolation unless VERY VERY carefully designed - and not as an integrated solution.
Its also why its important even with an ASync DAC to insure that the USB input is as free of unwanted Phase Noise as possible - hence why I believe that the Detox is a good idea (especially when its clock-locked to the DAC's USB port's clock).
Would that make a difference when using it for clock-locking?
This is getting more and more interesting, John!
fred sonnen
pfm Member
John
I do not understand how a GF cable can ad Jitter.
Do you have?
regards
F.S.
I do not understand how a GF cable can ad Jitter.
Do you have?
regards
F.S.
travelfotografe
pfm Member
JohnW
pfm member
The hard part of designing the clock-lock interface was to insure that the inherent Jitter of the Clock-Lock "Clock" signal does not degrade the clock in the Detox.
https://dl.dropboxusercontent.com/u/86116171/Detox Clock Proto.JPG
If you look at my Rats nested prototype circuit of the Detox Clocklock circuit in the above link you can see the x3 Crystals (Silver metal cans) - these are arrange to "filter" the incoming clock signal removing the Phase noise. The crystal filter only passes a very narrow signal bandwidth, any signal that falls outside of this bandwidth (Jitter Phase noise) is heavily attenuated.
https://dl.dropboxusercontent.com/u/86116171/Detox Band Pass.jpg
This rather phallic shaped filter characteristic (The final filter has a stopband attenuation of around -90dB) is the first stage of rejecting external Jitter on the Clocklock link, this is then followed by a PLL circuit with a very low frequency cutoff point to further attenuate any remaining jitter.
I'll verify the final performance levels on the "production PCBs" but after such lengths I don't expect (I'd like to believe) that the Detox is immune to external jitter.
JohnW
pfm member
Arh, yes - the OLED panels for you
, I collected it last month while in Asia. If you send an Email to Renata with your Address etc. we will post it to you
JohnW
pfm member
Fred,
It the very nature of the plastic fiber (Mutlimode) whose diameter is wider then then wavelength of light to transmit the light by bouncing the light energy back and forth off the walls of the fiber rather then a "direct" clean path though the fiber.
The leading edge of the incident wave front is made up of many photos of light, each having there own path length and hence arriving at varying at times and as a result the "broadening" of the received incident edge - its not a nice single clean pulse of light... Think of the effect of Multipath propagation in RF transmissions. As a result the cable is also HIGHLY vibration sensitive as the vibrations act upon the walls of the plastic fiber changing the reflected path lengths.
Also related is Modal dispersion:-
"Modal dispersion is a distortion mechanism occurring in multimode fibers and other waveguides, in which the signal is spread in time because the propagation velocity of the optical signal is not the same for all modes."
https://en.wikipedia.org/wiki/Modal_dispersion
JohnW
pfm member
In answer to your PM, your salvaged MDAC will be swapped directly for the FWC at no extra cost to you
Later I'll try and repair the salvaged units to turn them back into cash - but TBH I don't see me having the time...
JohnW
pfm member
I've no direct experience of Glass Fiber TOSLINK cables, but if they have the same diameter of "Glass" as I suspect they must to interface with the TX & RX detector windows then they will still suffer from the same Multi-path incident wave pulse distortion = edge jitter as Plastic fiber. They might have less "light loss, but this is not the primary cause of jitter.
Its not hard to perform these jitter measurement at such a crude level, so why dont the manufacturers of such wonder cables publish any supporting result to backup their claims?
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