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|6th May 2012, 07:17 PM||#1|
Join Date: Sep 2004
CD Transport Damping
After reading much of Peter Daniels old thread on the CDpro2 transport I thought I would make a separate thread rather than hijack his old post, to discuss some Damping ideas I have been thinking about.
For a while know I have been thinking about what to do with the Cdpro2 transport I have. I want to build my own Transport chassis for this drive. I have repaired a few of these transports and noticed that much of the top cover really serves little purpose. I have been considering making a solid top plate to rigidly mount the transport to. Peter's post CD PRO 2 - The making of a high end CD Transport shows exactly what I have been considering doing. But, thinking about the various types of vibrations I have been trying to figure out the best way to damp those vibrations.
So In thinking about this. we have several sources of vibrations. small vibrations from the sled motor. vibrations from the CD table motor and big vibrations from the rotating disc! Now the motor vibrations are in a single plane typically. but the disc vibrations are torsional and well as horizontal and vertical. (Plus air currents and possible static and magnetic interactions. but we will save those for later).
So we have a source of multi planar vibrations. and unfortunately what we really want isolated from those vibrations is bolted directly to the source of those vibrations! the laser sled!
Sony in the SCD-1 mounted the laser block to a massive chunk of aluminum and then moved the cd/table motor over the top of the laser block! which i think further illustrates what we really need to be looking at and focusing on. But going to that extreme I think is a bit out of DIY reach.
So 2 approaches I have been thinking about. 1- Mounting the CDpro2 assembly to a thick piece of aluminum, maybe 1" thick or so, with recesses cut out for the disc and finger access. with milled "X" patterns on the bottom side filled in with a heavy damping compound of some type. mounted on neoprene rubber bushings. two questions arise from this approach. would we want the top block that the transport is mounted to, to be as heavy as possible and then isolated from a standard chassis. or should the top block be mounted on isolators to an even heavier mass on the bottom?
The second approach really is the first approach but with the cd table motor removed from the CDpro2 chassis and mounted to its own separate mounting system/mass block. which then creates a whole bunch of interesting scenarios with the laser assembly mounted to a massive block and then should it that block be bolted directly to a large thick bottom plate or isolated from the bottom plate? should the motor be rigidly bolted to a mass or mounted with neoprene mounting system to a large mass or??
With the basic premise being, do we want a large mass at the source of vibration or do we want the source of vibration isolated from a heavy mass??
Zc <--Is thinking too much
It's not about what you can BUY...It's about what you can BUILD!
Last edited by Zero Cool; 6th May 2012 at 07:25 PM.
|7th May 2012, 07:46 PM||#2|
Join Date: Mar 2012
I'm new to CDs and this is all very fascinating.
One aspect you might keep in mind is that all the subsystems you are considering are in feedback control loops. Once you include these in your calculations, you have some pretty scary maths. In practice, for example, you might find that a remotely mounted drive to a heavy, softly-sprung spindle assembly provokes oscillation of the spindle or, in the case of an old philips, the radial motor.
You omit the option of adding balancing elements, which could be quite exciting. In-line twin counter-rotating drive motors, for example. Or square four or, for funky residuals, a 120 degree triplet. Balancing shafts too. Active weight is much more effective than dead weight.
How about complete slave mechs in push-pull, one for each axis? All rigidly connected, with the ensemble softly sprung?
On a practical note, I see that philips altered their suspension significantly in the CDM2/4 era. Originally they had the loader grounded and the laser/spindle assembly floating. This had been OK with the CDM1 but the lighter plastic versions ended up underdamped and oversprung, it seems to me. Also, the platter is left ambiguously floating between. Later, they rigidly attached the laser mech to the loader, and floated the whole caboodle. Hence the need for the flip-up cover attached to the fascia rather than the loader's nose. I guess that was mostly for the sake of increased sprung weight, but it also solved the orphan platter problem.
These days, those loaders are sick and tired of bashing up that cover, incidentally, and their belts are slipping. Such is the price of budget high fidelity. Please stop greasing them and then throwing them away, everybody, they are such good mechs...just clean them and wash and dry the belt please...
If only they had managed to make the radial and spindle motors out of plastic, sigh.
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