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Old 25th February 2003, 08:38 AM   #1
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Question CD Transportmechanics quality

Hi guys!
i got into a discussion today about what difference it would make between two discmechanisms, say a Sony and a Philips IF you use all the same electronics (same DAC, PSU and analogparts) ???

and another Q:
how important is the cabinet, ordinary sheetmetal case or 1 inch steel, in which way does the chassis affect the soundquality??

-help me out here please and i will be greatful for all times to come 8-)

/L
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Old 25th February 2003, 12:04 PM   #2
fezz is offline fezz  United Kingdom
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i belive both questons can be answered with: 'quite alot'

the case and disk transport are designed to mimimise interferance from the outside world (movement ect.) and different designers chose differenct ways of doing this.

dampening the case (adding weight and cutting down noise) is one of the best mods that can be done to a player - i have doen that to a relitivly cheap CD play and it sounds completly different
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Old 25th February 2003, 12:15 PM   #3
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Lightbulb CD-Transport Quality

Hi Mr. Triatec,
I changed from Sony to Philips recently.
Sound with my KWAK-DAC was distinctively better with the Philips.
I had a Sony CDPX33ES. I tried Philips CD-380 and CD-650. The CD-650 was slightly better than the CD-380.
I also tried the CDP-XA30 ES of my friend. It sounded about the same as my 12 year old Sony, provided I installed my clock.
I am not sure the difference in sound is due to the laserunit, the chipset or both. Mechanically the Philips is inferior to the Sony. The guys at Philips are thinking if we can make that part also of plastic we can save another 2 cent....
The Philips CD-650 weighs 3.5 kg. The Sony CDP-XA30ES 9 kg!

Also interesting: The sound of my old Sony is very digital unmodified; the Philips sounds OK in original condition.
I did not perform any mechanical mod so far, but I can make the Philips more heavy with "lead bitumen" dampening etc.
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Old 25th February 2003, 12:21 PM   #4
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Based on the experience of both myself and some friends of
mine, we have all experienced that there is a correlation
between good mechanical build and sound quality. This
would suggest that read errors are less frequent with a
good mechanics and a sturdy case. However, it is unclear if
this is the case. It has been discussed in a number of
threads previously, and some people argue that non-correctable
read errors are extremely rare. An alternative explanation
could be that no manufacturer would take the cost of a good
mechanical build unless the electronics is already very good
so the price can be justified. Still, if the players sounded as
good with a weaker build, it is hard to see why they would
bother about the mechanics at all, since this is a very expensive
improvement in manufacturing. Yet a possibility is that it is all
about vibrations interfering with the electronics and that it has
nothing to do with actually reading the disc. Still, for whatever
reason, I would say that yes, generally players with good
mechanical build will sound better than otherwise comparable
players.
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Old 25th February 2003, 01:10 PM   #5
fedde is offline fedde  Netherlands
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This is one of the issues I have been interested in for a long time, but I didn't find time to research it well. I wonder if read errors are common or if the differences are only because of jitter. I would like to make a test cd with some good wave files and then analyse the sp/dif datastream with some sort of a digital recorder. Then I could compare the original with the generated data stream to check for errors. I could try if things like "De Mat" on top of the cd will increase/decrease the amount of errors.

I think that the differences in sound quality from damping etc. are in the amount of jitter. If the laser assembly is unstable, more corrections of the servo are necessary to follow the holes of the cd. These servo corrections very likely influence the digital supply (give spikes on the supply) which will increase the amount of jitter. Regrettably, I do not have the equipment to check these thingies

Fedde

ps. in the case of cd-players instead of transports, sound changes will also occur due to IC vibrations and microphony of caps.
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Old 27th November 2003, 12:28 PM   #6
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In the past I have followed the path of mechanical tweaks.
Nowadays I consider a mechanism that needs all kinds of isolation
ready for the scrapyard.
Good shielding and some distance between pcb and casing is all I'm willing to provide myself.

Martijn
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Old 27th November 2003, 06:47 PM   #7
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Quote:
Nowadays I consider a mechanism that needs all kinds of isolation ready for the scrapyard.
They *all* benefit from it, just because of cost reducing measures manufacturers leave it out. What's wrong with adding damping material ? The mechanism benefits from it and it is not expensive so what is the problem ?

I have to admit that I prefer electronic modifications first, later followed by mechanical mods.
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Old 27th November 2003, 08:24 PM   #8
r0cket- is offline r0cket-  United States
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Quote:
Originally posted by fedde
This is one of the issues I have been interested in for a long time, but I didn't find time to research it well. I wonder if read errors are common or if the differences are only because of jitter. I would like to make a test cd with some good wave files and then analyse the sp/dif datastream with some sort of a digital recorder. Then I could compare the original with the generated data stream to check for errors. I could try if things like "De Mat" on top of the cd will increase/decrease the amount of errors.
I've thought the same thing many a time myself, mainly in regard to claims made here about the supeiority of one particular CD transport over another, or the boost in sound quality than an unintuitive modification made, etc. I mean, the truth is, digital is digital, and it's not all that complex. It's 1s and 0s and a timing component, and unlike analog audio where you can always invoke that tired claim that there's some mysterious, unmeasurable quality to your sound, every aspect of digital audio is, by definition, measurable. And it doesn't seem like it would be particularly difficult to actually go about measuring it--indeed, it seems like such a simple thing that you'd think some manufacturer would have done so already and would be trumpeting their results, but I've not heard of one doing so.
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Old 27th November 2003, 08:56 PM   #9
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Quote:
Originally posted by fedde
This is one of the issues I have been interested in for a long time, but I didn't find time to research it well. I wonder if read errors are common or if the differences are only because of jitter. I would like to make a test cd with some good wave files and then analyse the sp/dif datastream with some sort of a digital recorder. Then I could compare the original with the generated data stream to check for errors. I could try if things like "De Mat" on top of the cd will increase/decrease the amount of errors.
No need to go through all that trouble. Most every decoder chipset out there has error detect pins on it (usually flagging for both C1 and C2 errors) that can be monitored to see how many errors there are.

As Christer has already stated, this has been done and it's been found that uncorrectable errors are extremely rare.

Quote:
I think that the differences in sound quality from damping etc. are in the amount of jitter. If the laser assembly is unstable, more corrections of the servo are necessary to follow the holes of the cd. These servo corrections very likely influence the digital supply (give spikes on the supply) which will increase the amount of jitter. Regrettably, I do not have the equipment to check these thingies
Yes. John Atkinson at Stereophile uses the Miller jitter analyzer for testing digital components but I don't recall his ever using it to check for differences in jitter due to various CD tweaks.

se
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Old 27th November 2003, 08:59 PM   #10
fedde is offline fedde  Netherlands
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I agree that digital data can be transferred without errors theoretically. I don't know how many data errors are made by standard transports. The clocking of data is certainly measurable. Though it is not a matter of absolute jitter, but also of the jitter spectrum. Also, the jitter experienced at the DAC is relevant. So for example the shape of the waveforms also matters. Finally, what is important is the correlation of jitter properties with the experienced sound.

I really wonder why you would need a Pitracer (EUR 29000,-) to have a really good transport. I'd guess that a DAC with an extremely good clock and digital supply (fed back to the transport) should give similar results. If not better. I don't understand why you make an extremely expensive transport and then transfer the data in S/P-DIF format and use 50 ohm tulip connectors...

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