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Old 15th December 2002, 06:20 PM   #21
dorkus is offline dorkus  United States
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is fanout such a critical issue to jitter performance? i suppose it depends on what is driving the lines, but if we use a high enough performance buffer (e.g. the comparator in the Kwak clock) wouldn't the degradation from driving multiple lines be minimal? i think it would be good to buffer the 4th line going to the digital board, since it will be the most reactive (ribbon cable to remote board, longer traces, etc.) but shouldn't isolation resistors on the three lines be sufficient for the DACs?
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Old 15th December 2002, 06:25 PM   #22
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Quote:
Originally posted by dorkus
is fanout such a critical issue to jitter performance? i suppose it depends on what is driving the lines, but if we use a high enough performance buffer (e.g. the comparator in the Kwak clock) wouldn't the degradation from driving multiple lines be minimal? i think it would be good to buffer the 4th line going to the digital board, since it will be the most reactive (ribbon cable to remote board, longer traces, etc.) but shouldn't isolation resistors on the three lines be sufficient for the DACs?
Hi

Fan out is critical, but yes, it all depends on the driver. However, I want separation from all devices that are driven, so I do not mind more than 1 buffer, and the use of series resisitors.

What buffer does Elso use ?

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Old 15th December 2002, 06:41 PM   #23
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one other question... does it matter if the clock of one DAC or part of the circuit is inverted with respect to the clock of another DAC? or did you mean to use two inverters in series to retain phase? is the performance of an hex inverter superior to a hex buffer?
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Old 15th December 2002, 06:46 PM   #24
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Quote:
Originally posted by dorkus
one other question... does it matter if the clock of one DAC or part of the circuit is inverted with respect to the clock of another DAC? or did you mean to use two inverters in series to retain phase? is the performance of an hex inverter superior to a hex buffer?
Hi

Mutual clock phase: I'd say both channels need same phase, but it will depend on the DAC chip, and the accepted error. BB PCM63 converts at downgoing slope at LE, so there will be small delay between both channels.

Quality of buffers, inverters: The induced jitter depends on the type of logic, and the design of the circuitry, there is no generic answer here.

Less is better, applies here as well........

enjoy
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Old 15th December 2002, 08:18 PM   #25
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Lightbulb Clock

Hi Dorkus,
What's in my clock can be found here:
clock upgrade for cd/dvd players
From the datasheet of the AD8561:
<B>"</B>
<B>OUTPUT LOADING CONSIDERATIONS</B>
The AD8561 output can deliver up to 40 mA of outputcurrent without any significant increase in propagation delay. The output of the device should not be connected to more than twenty (20) TTL input logic gates, or drive a load resistance less than 100 Ohm.
<B>"</B>
Hope this helps.
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Old 16th December 2002, 05:07 PM   #26
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Default Re: Clock

Quote:
Originally posted by Elso Kwak
Hi Dorkus,
What's in my clock can be found here:
clock upgrade for cd/dvd players
From the datasheet of the AD8561:
<B>"</B>
<B>OUTPUT LOADING CONSIDERATIONS</B>
The AD8561 output can deliver up to 40 mA of outputcurrent without any significant increase in propagation delay. The output of the device should not be connected to more than twenty (20) TTL input logic gates, or drive a load resistance less than 100 Ohm.
<B>"</B>
Hope this helps.
Elso,

Nice statement from AD, but does it tell you anything on the jitter the comparator gives ?

The "static" prop delay is about 2 ns/V. Luckilly the device has a high PSRR, but that is not specified as function of frequency.

Since AD does not specify anything on induced jitter, I'd suggest to measure it.

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Old 16th December 2002, 05:32 PM   #27
dorkus is offline dorkus  United States
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i don't know if anyone's measured the jitter of Elso's clock but i suspect it's very low. or at least it sounds extremely good by all reports, so we can only assume the jitter is low.
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Old 17th December 2002, 04:17 PM   #28
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Quote:
Originally posted by dorkus
i don't know if anyone's measured the jitter of Elso's clock but i suspect it's very low. or at least it sounds extremely good by all reports, so we can only assume the jitter is low.
Dorkus,

I have heard thousands of people being enthousiastic about heavilly distorting amplifiers. At the risk of raising a different thread, the only thing that I want to make clear is that measuring at least gives more grip on the subject.

I never listened to, or measured at Elso's clock. I am sure about one thing: The lower the jitter, the better.

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Old 17th December 2002, 04:19 PM   #29
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ok, fair enough. i will try Elso's circuit first, since i can build it out of off-the-shelf parts, and then perhaps compare to your module.
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Old 26th December 2002, 10:04 PM   #30
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dorkus,

If youre not done yet with your mod I strongly suggest you continue.

All the way from the SCD-XB940 up to the SCD-1 flagshipp and its brothers, they benifit greatly from a new clock.

/Peter
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