Mods to the SPDIF output of a CD transport - diyAudio
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Old 13th July 2004, 11:15 AM   #1
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Default Mods to the SPDIF output of a CD transport

All,

A couple of questions on SPDIF mods:

1. Is it possible to reclock the SPDIF output just before it leaves the transport or after it enters the DAC using a simple 74HC74 with an asynchronous clock? What impact/benefit does this bring?

2. Sometime ago, ELSO published his SPDIF interface which uses an OPA603 driver. Excuse the ignorance, but can BUF634 be used instead? Also, does the input of the DAC need to be modded as per ELSO's original post, or does that not matter?

Thanks
Ryan
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Old 13th July 2004, 11:20 AM   #2
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Lightbulb Re: Mods to the SPDIF output of a CD transport

Quote:
Originally posted by Dr.H
All,

A couple of questions on SPDIF mods:

1. Is it possible to reclock the SPDIF output just before it leaves the transport or after it enters the DAC using a simple 74HC74 with an asynchronous clock? What impact/benefit does this bring?

2. Sometime ago, ELSO published his SPDIF interface which uses an OPA603 driver. Excuse the ignorance, but can BUF634 be used instead? Also, does the input of the DAC need to be modded as per ELSO's original post, or does that not matter?

Thanks
Ryan
Hi Ryan,
I think it can be done but as said earlier I would reclock after the DIR or after the digital filter in the DAC. I am not going to explain this again.
The AD810 seems to be a nice replacement for the obsolete OPA603. The latest scheme also works with a standard DAC input with digital transformer as it has standard SPDIF output level.

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Old 13th July 2004, 02:01 PM   #3
borges is offline borges  Norway
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Ryan,

The cleanest possible clock in a CD drive, wouldn't that be the oscilator that clocks the drive itself?

Does your drive only have an SPDIF output available? If that is the case, I would decode it and pair it up with the oscilator clock.

If you have other options than SPDIF (I2S etc) available, see if your filter/DAC supports that format.

For my latest DAC board I actually have the option of choosing between CS8414 output and internal CD player signals (among them the crystal freqyency divided down by 2).


Greetings,

Børge
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Old 13th July 2004, 02:36 PM   #4
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My PS audio transport reclocks the output with a ALS74 at the outputs. The signal is feed from Q and QNot right into the transformer, there is an impedance match their. Of course if you don't have a really good clock like Jocko or Elso it still will jitter even after it's reclocked. Ground noise in the transport can really impair the performance of the SPDIF.

I have modified the clock in my transport several time now, so the better clock the better the sound. I believe it better to remove the jitter at the cource of course you can use a sample rate converter to reclock the data in the dac. In fact I do both.
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Old 13th July 2004, 03:08 PM   #5
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Thanks for the responses.

Why would sonething like a BUF634 be useful to drive the coaxial cable? Why the need for a OPA633 or AD810? Cretainly OPA633 is just a buffer, like BUF634.

Jewlson: I was think more along the lines of using a simple 74HC74 fed from a separate clean clock. How do you do your reclocking? Is the ALS74 being fed from the master clock in the transport or a seperate clock (with its own power supply...)

FYI, I have a Proceed PDT3, which drives a Theta DAC. The Theta has extensive post CS8412 reclocking.

Thanks
Ryan
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Old 13th July 2004, 04:24 PM   #6
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Using an high speed opamp would not be my first choice. I used the ALS part because of it's low ground bounce noise.

All HC parts can under shoot the ground do to the output design which can lead to noise.

The ALS is feed from a modifed master clock, I stongly recomend you purchasing a after market one from Jocko Homo. The are some other good one too.

The 8412 is only marginal good at removing jitter from the incoming signal. The power for the receiver has to be very low noise for it to work well. The PLL in side the chip is not so great.
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Old 14th July 2004, 07:30 AM   #7
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Quote:
Originally posted by jewilson
Using an high speed opamp would not be my first choice. I used the ALS part because of it's low ground bounce noise.

All HC parts can under shoot the ground do to the output design which can lead to noise.

The ALS is feed from a modifed master clock, I stongly recomend you purchasing a after market one from Jocko Homo. The are some other good one too.

The 8412 is only marginal good at removing jitter from the incoming signal. The power for the receiver has to be very low noise for it to work well. The PLL in side the chip is not so great.

Hi

Are you suggesting that ALS logic does not sugffer from cross current ?

On the contrary, these gates are that fast that the excitation of the drain source capacitor induces "cross current like" currents again.....

cheers
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Old 14th July 2004, 08:39 AM   #8
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Question Smoke Curtains

Quote:
Originally posted by Guido Tent

Hi
Are you suggesting that ALS logic does not sugffer from cross current ?
On the contrary, these gates are that fast that the excitation of the drain source capacitor induces "cross current like" currents again.....
cheers
Guido,
So, which logic family do you recommend?
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Old 14th July 2004, 02:28 PM   #9
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Default recomendation please..........

OK Guido, what are your recomendation.

Also, the only place I know of cross-currents is in the ocean, you must fill me in this idea. Maybe you’re talking about circulating ground currents?

Anyway the facts are that the push-pull outputs of the CMOS device "can" under 0 volts or ground. Of course some CMOS logic families are worst than others.
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Old 14th July 2004, 03:16 PM   #10
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Default Re: Smoke Curtains

Quote:
Originally posted by Elso Kwak

Guido,
So, which logic family do you recommend?

I prefer the tradeoff between required speed (slope), drive capability and cross current.

Sometimes that is HC, sometimes HCU, sometimes ACT, sometimes even HEF, it depends on the application.

I was triggered because Jewilson stated that ALS would produce lees switching current......

cheers,
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