Increasing CD platter inertia

[poynton]

Andy ,
have you SM for that player ?

Hi.

Yes, I do.


Andy

 

[Zen Mod]

Hi.

Yes, I do.


Andy

any posibility to share it - at least schematic ?

I have just recently resurected DP-1100 (without SG) ;
you'll not believe - I bought it on flea market for ~ 3Euro , and found that is broken ( surprise for that price ) ; culprit was shorted elko in 5V reg circ part .......

TIA

 

[poynton]

I will be back in the UK in about 6 weeks.

I will scan the diagrams then.


Andy

 

[lcsaszar]

It is interesting to see that this thread resurfaced. I read it through once again. It seems there is a concensus that increasing inertia of the DC platter just burdens the motor and has no benefit, apart from reducing the mechanical vibration and thus reducing bit errors. Even bit errors may not be audibly detectable. C1 errors are perfectly corrected. C2 errors are interpolated if there is an error frame between two good frames. If there are more than one error frames between two good frames then the error frames are muted.
Actually I installed a LED that indicates C1 and C2 errors. It blinks on some out-of-the-box audiophile CDs, and does not blink on some scratched old CDs. Maybe pressing errors dominate over read errors, I don't know.
What I was thinking about is the analogy between inferior sounding servo-controlled direct-drive turntables, and superior sounding high-inertia belt-driven turntables, and their counterparts in the world of CD mechanisms. Could we eliminate the servo in CD? Probably not. But what if we add a high mass when the speed has stabilized, and use a slow servo for slowly adjusting the angular speed from the beginning of the CD to the end? Then the variance of the angular speed (I call this mechanical jitter - phn, are you still with us?) will be minimal. But of course the servo will regulate the speed (only at slow pace) so that the RAM gets filled around 50% at any instant. Practically, the frequency of the data stream at the input of the RAM will be equal to the frequency of the output data stream. It is so with the current fast servo, as well, but there is high variance of frequency (you can call it jitter) around an average value.
Theoretically it should not make any difference, but we learned hard that there IS a difference in many cases where there should not be.

 

[Zen Mod]

I will be back in the UK in about 6 weeks.

I will scan the diagrams then.


Andy

TIA

 

[mr-mac]

I belive most of the diffrence between external transports is either in the clock induced jitter or earthing... Below is a quote from John Westlake and I would tend to trust his information.

Maybe damping the transport allows for less vibration to be transferred into the case and other components (as I think cheap cd players are improved by damping the case (esspecially if you look at the stats in point 1 of John Westlakes information).... Maybe if you could place an anti vibration support below the CD player and actually mount the transport to it with spikes and the usual soft mountings on the drive so there is no mechanical connection between transport and rest of player you would see a lot more improvement. Kind of like TT's where motor is actually set seperatly to rest of TT.

I would agree that a better damped transport may allow less motor citcuit noise etc. to get into the digital data. So maybe a combined approach of damping drive and mounting it seperatly might be a very intresting idea.

1. Data Accuracy

This is the most basic function of the transport – with a correctly functioning CD player and reasonable condition Disc the audio Data will be 100% Bit accurate, this means that the Data that was originally recorded on the Disc during Mastering is fully recovered Bit for Bit – in the worst case (this assumes reasonable condition Discs) I’ve never seen more then 50 “interpolated samples” of error across the whole disc – now consider that a 60 Minute CD has 158.76 Million samples, there’s no way that anybody could reasonably argue that 50 “interpolated errors” can effect the GENRAL OVERALL audio quality – by this I don’t mean when the disc skips etc.

2. SPDIF Output Phase Noise (Jitter)

This is where Digital meets the realms of the real world – same Bit for Bit accurate Data but very different sound between Transports and even Interlink cables etc etc????

Lowest Jitter will not always guarantee best audio performance (It very much depends on what happens down steam at the DAC) – it’s the distribution (signal content) of the Phase Noise that is critical, types of Phase Noise that is ALLWAYS detrimental :-

A. DATA correlated artifacts. These are signals or spurie within the Phase Noise plots that are directly correlated to the “Data processing” of the CD transport such as spurie from the CD servo sections, Data recovery and error correction, control MCU etc.

B. Fixed frequency Non Data correlated discrete artifacts, such as mains hum, non synchronies Front panel displays & MCU’s etc.


3. RF & Earth Leakage Current introduced Phase Noise spurie & noise products.

The effects of RF & Earth Leakage Current should not be underestimated, they can effect the DAC (and audio system) via any electrical inputs (SPDIF), audio outputs (via the Feedback path of the output Opamps), and the mains supply input.

Re the quote about meridian drives (I guess using CD rom drives). Well they have one advantage. The read ahead and can actually attempt re-reading the data 3 times if it gets a read error. I think this will likely minimize any disadvantage it has being a cheaper plastic drive. A normal CD transport only gets one chance at reading the data.

John

 

[lcsaszar]

Maybe a bit off topic. How do computer CD transports work when playing audio? Are they spinning 1x speed, or spinning at max speed and re-reading the same data? In the last case the same error correction could be realized in hardware as EAC does in software.

 

[mr-mac]

I belive in the case of meridian they are neither running a 1x or maximum speed.

they run at speed somewhere above 1 (maybe in the 4x ish area). This allows them to pre-read the data into the buffer and to be able to re-read areas if it gets a read error. But also means the drive is spinning slow enough that it doesn't create lots of audible noise or vibration

John

 

[Scorpio(DDMF)!]

Just a thought:

Wouldn't using cd-rom mechanisms set to "extraction mode" and tuned to 4x CAV speed (for example) greatly reduce the need for & complexity of vibration management in a CD transport?

Since the rotation speed is constant (4x) throughout the whole disc, wouldn't the number of resonating frequencies be greatly reduced compared to a conventional (rotation speed-changing) system?

Also, a possible implementation of pre-read would be a very nice "side effect" of the process

Cheers!

 

[mr-mac]

Maybe thats how they do it.. but I guess it runs a little faster to get data into the buffer and needs to change speed as the laser moves accross the disk anyway.

Some computer CD roms are self balancing (ie very quiet even at 40+ speed (very usefull as most CD's are not perfectly in balance to start with).

Self balancing combined with low speed would be quite good from a vibration point of view.Would still take the top plate off the drive case (as it's quite resonent and want to bolt drive to somthing with mass).

John

 

[geneticaurora]

How about a better grip as opposed to more weight?

 

[martin clark]

thread necrophlia!

You do not need more clamp grip if the mechanism reads the TOC correctly (i.e. loads & initialises the disc at all).
That point is the maximum rotational acceleration applied!