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Old 11th January 2017, 02:26 PM   #91
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74HC74 outputs 25ma..not ideal
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Old 11th January 2017, 02:45 PM   #92
peufeu is offline peufeu  France
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What is the problem with 25mA ?

Other option is RS485 transmitter (the 25 Mbps ones).
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Old 11th January 2017, 02:54 PM   #93
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Quote:
Originally Posted by peufeu View Post
...or use optical and WM8805, which just works...
peufeu, I've been wondering about TOSLINK jitter suppression via the WM8805. Have you seen much of an increased pass through of jitter from TOSLINK versus coaxial S/PDIF?
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Old 11th January 2017, 03:20 PM   #94
peufeu is offline peufeu  France
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Copper or optical are indistinguishable when measured with my soundcard...

It's a digital Frac-N PLL, every few seconds it'll update its frequency a little bit to follow the input, but between updates frequency stays constant, so it doesn't really care about incoming jitter.
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Old 11th January 2017, 03:24 PM   #95
TNT is offline TNT  Sweden
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Toslink is lower bandwidth therefore higher jitter (if both are implemented ideal).

If real re-clocking is performed in the sink, toslink solution is preferred as it will inject less disturbances from the source. In this case, the level of jitter is not crucial as clocks are re-generated. This is however not always true for a PLL as its HP filter is often to high. This frequency don't seem to be specified in the WM8805 data spec sheet? It only specifies the jitter it adds (intrinsic).

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Old 11th January 2017, 03:39 PM   #96
peufeu is offline peufeu  France
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If you use two scope channels to look at SPDIF input and BCK output on the scope, you'll see them smoothly and very slowly slide one relative to the other... then after about a second, it updates its frequency and the signals slide the other way... then it repeats.

No idea about the corner frequency though... also, it might update its frequency more often if the source clock is less stable, which would make the corner frequency dependent on the source...
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Old 11th January 2017, 04:05 PM   #97
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Originally Posted by TNT View Post
Toslink is lower bandwidth therefore higher jitter (if both are implemented ideal)...
Also, Toslink features air gaped butt connectors, which is a recipe for optical impedance mismatching. As we know, impedance mismatching, whether galvanic or optical, induces interface jitter. I seem to recall seeing optical index matching gel being marketed somewhere for the purpose of bridging Toslink connector air gap, giving an refractive index better matching that of the fiber. In optical's favor, of course, is that it doesn't couple common-mode noise across the interface, which could otherwise induce jitter at the receiver circuitry.
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Last edited by Ken Newton; 11th January 2017 at 04:12 PM.
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Old 11th January 2017, 04:52 PM   #98
Shinja is offline Shinja  Japan
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wolfson states it is 1Hz! in the document "A_high_performance_SPDIF_receiver_Oct_2006".
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Old 11th January 2017, 07:25 PM   #99
Gusser is offline Gusser  United States
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Quote:
Originally Posted by peufeu View Post
What is the problem with 25mA ?

Other option is RS485 transmitter (the 25 Mbps ones).
An ideal way to drive 75ohm SPDIF is to use a video OPAMP or line driver. Maxim makes a plethora of options.

Now this is hardly cost sensitive for mass market consumer products but is a very good 75ohm line driver.

SPDIF and AES-3 can be treated as NTSC/PAL analog video up to 96khz. You can use stock video switchers and distribution amplifiers. The only thing to watch out for using pro video amps and switches is sync tip clamping options that are no good for AES/SPDIF.

For balanced AES, yes commodity RS422/485 drivers and receivers are a good choice. I do it all the time - but they should be capacitor and transformer coupled.

Last edited by Gusser; 11th January 2017 at 07:28 PM.
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Old 12th January 2017, 02:00 PM   #100
TNT is offline TNT  Sweden
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Originally Posted by Shinja View Post
wolfson states it is 1Hz! in the document "A_high_performance_SPDIF_receiver_Oct_2006".
OK! So below 1khz, all jitter from the s/pdif link is passed to the DAC

Ma - where did the bass go?

Or was this with digital PLL updated every 2 seconds? Then it doesn't matter I suppose.

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Last edited by TNT; 12th January 2017 at 02:03 PM.
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