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thoriated 11th September 2006 03:15 PM

Interesting results from dust cover upgrade
I recently made my own dust cover to replace the one that came with my Linn Sondek, with the view of isolating it from air borne vibrations as much as possible.

I used .200" thick smoked acrylic for the front and back panels and two .100" thick pieces of smoked acrylic separated by an air gap of ~0.125" for the top. For the side panels, I sandwiched acrylic, lead and red oak (from inside to outside) to make sound reflecting and damping panels.

I had already replaced the bottom board of the Linn with two 3/8" thick sheets of baltic birch plywood laminated with a 0.125" thick sheet of lead in the middle. (I had drilled out part of the lead sheet on the platter side to balance out the overall weight on the four Air Pod AP1 isolation feet which I've been using with the Linn for years.) This, I think, has been quite effective in isolating from structure borne vibrations, short of mounting the whole turntable on a half ton concrete platform located in the basement. I should mention that none of the lead I used is exposed to the environment - it's all encapsulated by solid sheets of wood or acrylic. I estimate that the whole turntable & these enhancements weighs around 35 lb now.

The effect of adding a dust cover that really isolates the turntable from air borne vibrations (as well as the base damping/isolation that isolates from structure borne vibration) is very worth while. In particular, I noted a naturalness of tone and low level detail throughout the mids and highs that I'd never heard to nearly this extent before from the Linn. Cymbals and upper harmonics of instruments on many recordings stand out more clearly than before and lost coloration with the result that there is a significant enhancement of their true to life representation. Image stability was consistently rock solid. Of course, detail (already excellent with the custom base and Air Pods) also improved with the dust cover change, but I haven't yet listened to enough recordings to exactly quantify that.

The only real downside to the new dust cover is that it is quite heavy (several pounds) and it is hard to lower all the way (considering that the whole assembly tends to rock on the four Air Pods when I do) without causing the stylus to skip. I have a fix in the works for this, however.

thoriated 25th August 2009 09:50 PM

New way to correct tracking angle?
I thought I 'd add this to an old post that I never got any response on to 'refresh' it.

I believe it would be possible to create a tonearm that would maintain a perpendicular tracking angle by implementing its bearing to adjust the overhang depending on the arm angle. I wonder if anybody has ever tried this? It would seem that, if friction is kept low, it would provide most of the benefits of the linear tracking tonearms. A version could even be made that didn't require antiskating, but it would require excessive horizontal bearing repositioning, IMO.

Btw, this is not the Garrard articulated headshell idea. The only bearing(s) would still be at the base or pivot point of the tonearm.

Also, thinking about this, it might be possible to create a type of tonearm (perhaps facing in the 'wrong' direction) coupled with this bearing approach that possibly could actually compensate for the speed variation of off center records.

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