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[OM] OT: audiophile's news

Subject: [OM] OT: audiophile's news
From: "Lama-Jim L'Hommedieu" <lamadoo@xxxxxxxx>
Date: Fri, 23 May 2003 01:51:00 -0400
I apologize for this off-topic post.  I hope that I've proven to a be a 
helpful, if sometimes quick-tempered member and will allowed
to be off-topic this once.

I put my LP turntable on the wall.  This might not sound like a big deal but it 
is.  Ten years ago, I bought "shelf brackets" and
put up a particle board shelf.  How hard could it be, right?

Shelf brackets are not competent to hold up a turntable.  For one thing, the 
center of mass (of my relatively modest Rega Planar 3)
is about 7" from the back of the table.  But I had to position the back of the 
table away from the wall to use the hinged cover.
That pushed the center of mass out to about 9" away from the wall.

There were other problems: store bought brackets are triangulated jobs, meant 
to support the weight from underneath.

I took phyics in college and we covered "statics".  Supporting the weight of an 
object from the bottom is all wrong.  With the
center of mass 9" out from the wall, even if the bottom of the triangle is 9" 
below the shelf, the weight will pull the top bolt out
of the wall.  The weight of the table is pivoting (through the moment arm), on 
the bottom of the angle bracket.  That means that the
weight of the table is now a TORQUE on that top bolt.  Over months, it will 
slowly pull the bolt out of the wall.  That's not a load
that a in-wall anchor is meant to take!  It's meant to be loaded straight down.

So, I bought 5' long vertical rails and shimmed them so they're plumb to a load 
bearing wall.  It's a brick wall.  I put lead lag
shields into the brick wall.  I put the table near the bottom of the 5' tall 
brackets, so the weight of the table sits nearly
straight down on those lead lag shields.

In Stereophile, I read that a great way to isolate a turntable is to use a sand 
bed.  A physics major at work confirmed that a sand
bed is one method of isolating a platform from seismic vibrations for making a 
hologram.

I didn't buy a sand bed though.  I bought the biggest stamped-steel, one piece 
tray I could find.  (A roasting pan!)  I loaded that
puppy with 22 pounds of aquarium gravel (still in the bags).  I put it on the 
floor next to the refrigerator for 3 weeks to let the
vibrations make it settle out.  I'm not worried that the pan will split out.  
It's thick and has a rolled edge.  (I'm still
wondering though, why a roasting pan, ANY roasting pan cost $20 USD.  I could 
almost buy a 50mm 1.8 mij for that.)

In Stereophile, I read that mass-loading a sand bed is a good thing.  Here I 
was very, very lucky.  In the basement I found a 24
pound, machined block of some slippery-smooth rock.  I'm thinking it is 
sandstone.  The top and bottom are machined parallel, like a
gravestone.  It sits on the gravel, just inside the roasting pan without 
touching the walls.

I put a steel-wire shelf down, loaded the shelf brackets with the 46 pounds and 
let it sit there 24 hours.  Then I torqued the bolts
gently again and installed the table.

Result:  This is the first time in my 47 years on the planet that the plinth 
doesn't jump around when I lift the dustcover.

The sound might be a bit more stable but I'm using the backup cartridge so 
there's just not much quality there to work with.  (In an
industrial accident, I destroyed the cantilever on the good one.)

Here's my plan for the next generation: I'm selling off my trailing-edge NAD 
preamp.  I'm replacing it with a very recent integrated
amp with a moving-coil card.  After that, a new moving-coil cartridge will be 
the final touch.

Cool, huh?

Did anyone read all of this?

Lama


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