CDM-1 servos (Marantz CD-12 aka Philips LLH1000) - diyAudio
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Old 10th February 2004, 07:55 PM   #1
tvdw is offline tvdw  Belgium
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Default CDM-1 servos (Marantz CD-12 aka Philips LLH1000)

I have recently acquired a Marantz CD12-DA12 combo. It features a die cast CDM-1 mechanism from Philips. Does anyone know if it is possible to replace the analog servos by digital servos? I would also like to know which changes to the clocking system yould be advisable and which op-amps I could change.

Other suggestions for improvement are also welcome...
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Old 11th February 2004, 07:14 AM   #2
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Default Re: CDM-1 servos (Marantz CD-12 aka Philips LLH1000)

[QUOTE]Originally posted by tvdw
I have recently acquired a Marantz CD12-DA12 combo. It features a die cast CDM-1 mechanism from Philips. Does anyone know if it is possible to replace the analog servos by digital servos? I would also like to know which changes to the clocking system yould be advisable and which op-amps I could change.

Other suggestions for improvement are also welcome...

------------------------------------------------------------------------

First thing you should do is to look at the dac power supply rails. The digital and analog stages in the output section are not separated and very noisy.

The transport is rather copmples electronically and 'touching' it may be a BIG job.

Despite the hype, not a particularly good sounding combo by modern standards.
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Old 11th February 2004, 08:51 AM   #3
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Quote:
Despite the hype, not a particularly good sounding combo by modern standards.
yes.......if you feel like gettin' rid of this old cd combo - shoot me a mail......
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Old 11th February 2004, 08:59 AM   #4
EDUM is offline EDUM  Netherlands
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Of course you can replace the analog servo with a digital one.

But why would you do that? The CDM1 servo is still one of the best. And indeed developping a digital servo is a hugh task. Do not forget that a CDM servo is a compromise. Different disc errors require a different approach. Approches often conflicting whith each other. Knowing what to look for takes a lot of experience. Finding that servo optimum is very interesting but it is very very time consuming.

Ward
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Old 16th February 2004, 06:45 PM   #5
phi is offline phi  Sweden
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Default Servo Problems ?

Hi,

As I see that we have EDUM on this thread and he seems to know quite a lot about the Philips transports, I thought I would give it a try. But anyone with a good advice is welcome

I have a Marantz CD-80 thats works perfectly except for not accepting the records now and then. If the record is not accepted you just have to open and then close the transport and it works fine. Any simple solution to this ? Is it just is too fast for it's self sometimes ?

I also have a CD-75DX (CDM-4/11 transport). And this one is having a lot more trouble. It can always read and play the records but if you start to jump between tracks then the trouble starts, and the higher the index, the further out the laser is on the disc the more troble it has. It works hard for quite a while making a lot of noise and sometimes it will find the next track sometimes it won't. At some point it will always just crach i.e. it will kick the laser unit traight out banging it to the outer limit of the laser unit. Is there a servo problem, of course there is, but is it due to the laser starting to get old or is it due to some other fault ? I have upgraded all the electrolytic capacitors.

/phi

Everything matters
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Old 17th February 2004, 08:00 AM   #6
EDUM is offline EDUM  Netherlands
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As in most cases regarding playability there are often more effects that can cause certain behaviour.

What happens if you open and close the transport/tray? In most cases the disc position with respect to the spindle/ motor axis is different from the situation previously. In other words the disc eccentricty and the eccentricity of the "turntable /motor axis" is differently. So sometimes when the eccentricties are adding up it just becomes to much.

Now why is it to much can be the result of fingerprints in the start up area, a wobble in the disc, an inclusion in the disc, a dent in a disc etc, etc. But also a problem with cdm mechanics,the turntable or servo electronics.

So what is happening is often quite easy to explain, what causing it is mostly not straight forward.

For the CD-75DX you can hear it strugling! Something is causing radial trouble. At a certain moment control is lost. Besides the above mentioned possible causes for radial problems I do not trust old cdm4's entirely. (no scientific reason, just seen to many "strange" behaviour). I would check how easy the arm can move (power-off). Although officialy not recommended you can use a bit of oil to make the arm hinge move a bit more easy.

what capacitors did you change on the cdm?

Success!

Ward
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Old 17th February 2004, 05:54 PM   #7
phi is offline phi  Sweden
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Quote:
What happens if you open and close the transport/tray? In most cases the disc position with respect to the spindle/ motor axis is different from the situation previously. In other words the disc eccentricty and the eccentricity of the "turntable /motor axis" is differently. So sometimes when the eccentricties are adding up it just becomes to much.
Yes, can only agree with you. I have only had experience with CD players with a digital servo control before and there I have never experienced any kind of disc-rejection. It is perhaps/probably easier to ajust/adopt the servo behavior in a digital servo design for the different types of behavior needed.

Are you by the above saying that it is common behavior that these old analogly servo controlled players behave in the way you decribed ?

As for the CD-75DX: The arm is moving perfecley, no problem. I did however put some new grease on the centertap of the squeezing mechanism and that decreased the audible noise quite a lot.

I have changed the PS caps (caps = electrolytic ones, except the cerafines), the PS caps around the motor drive amp etc. A small green one I have still not changed (Nichicon, Muse, 1.5uF). It placed somewhere around the motor drive amp.

There are some caps on the PCB's on the CDM4, but I have not touched those.

/ Phi

P.S. By the way, do you know anything about philips CD 618 ? Transport ? (It's a bitstream machine, that much I know, and it looks a bit like the CD88X machines) Have not found it among all the listings here at DIY.

Here is a picture of the CD-75DX playing music
and below the CD-80.
Attached Images
File Type: jpg cd75dx.jpg (58.3 KB, 669 views)
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Old 18th February 2004, 08:32 AM   #8
EDUM is offline EDUM  Netherlands
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I guess it possible to make a digital servo with a better behaviour as an analog system. For any CDP however manufacturer cost is a driving factor. Meaning that they will adopt a digital servo as it becomes small and cheap in large quantities. But if you would spent a lot of effort on it you could make a digital servo with near ideal behaviour. However the real value of such a system is in playing stained, scratched and damaged CD's. Taking care of your CD's is easier.

Most older players simply suffer from aging. Readjustment, cleaning and replacing weared ou parts mostly do the job.

I checked a CD player sometime ago which was quite noisy. It turned out that the clamp was slightly touching a plastic part of the loading. After putting a piece of carton under one of the legs(?) it disappeared. Such a thing (or a wire touching the flexprint) influences the available headroom for tracking.

CD618 has a CDM4/19


Ward
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Old 18th February 2004, 08:09 PM   #9
phi is offline phi  Sweden
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Hi and thanks for answering patiently !

I won't torment you with any more questions for now.

Now it's time to digg into the electronics...

/Phi

P.S. I did try to put a home made magnetic clamp on and the transport and it got even more quiet !!! (Don't know if I by this detune the dampingsystem of the transportunit, but it seems to work fine anyhow
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Old 14th April 2006, 02:43 PM   #10
dp01 is offline dp01  Portugal
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Quote:
I also have a CD-75DX (CDM-4/11 transport). And this one is having a lot more trouble. It can always read and play the records but if you start to jump between tracks then the trouble starts, and the higher the index, the further out the laser is on the disc the more troble it has. It works hard for quite a while making a lot of noise and sometimes it will find the next track sometimes it won't. At some point it will always just crach i.e. it will kick the laser unit traight out banging it to the outer limit of the laser unit.
I have also a CD-75DX, haven't modifeyed it yet, and it's the best player i have ever saw, it has almost 20 years, and it still reads cd-r's perfectly! (off course that if i put a damaged disc, it skips a little).... my sony DVP-S535D stopped reding dvd's after 1 year of use (~310h DVD and 80h CD)...
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