NOTE: the sandbox described below was designed to accommodate the T-base pulley drive system of my original TNT-1. I continue to use the same box, but the top plinth has now been upgraded to accommodate the single motor/flywheel arrangement (sorry, pic not provided). The pulley support pillars, being obsolete, have been removed. The top plinth is now split with separate plinths under the motor/flywheel and main turntable. The undersides of both MDF plinths have been covered with aluminium angle (screwed and glued) to provide greatly increased stiffness and contact with the sand in the base. The new split plinths with finned bottoms make the turntable sound significantly more neutral and resolute.
I originally made a basic sandbox using an MDF bottom with pine sides
nailed and glued to the base. Outside dimensions were 720 x 570 x 140mm (LxWxH),
this would allow me to insert a plinth large enough for the TNT without touching
the inside edges of the box. The top plinth (painted MDF) had circular cut-outs to provide
isolated support for the TNT's separate motor assembly. Unfortunately I underestimated the weight of sand
required to fill such a box. It was extremely heavy and I was unsure whether the
18mm MDF base would support the weight. In addition to the weight, the small
circular cut-outs (which I proposed to support the TNT motor base with) sank into the
sand and couldn't be levelled properly.
I shelved the project for about 12 months.
Eventually I decided to have another crack at the project.
First, to reduce
the sand weight and stiffen the base, I nailed and glued a few pieces of scrap
pine to the bottom - the base was now ~36mm thick. Then I screwed on stronger steel corner braces and a
diagonally placed piece of angle iron for overkill (since it was lying around in
my shed).
I was considering what to use for the motor assembly supports, when a friend suggested
setting the threaded rod into PVC pipe with cement.
Ironically the hardest
thing to source for the project was the sand. Taking
Note:
For those unfamiliar with the TNT series 1 turntable, it consists of two main pieces:
(1) The T-shaped motor/idle-pulley base, which sits on three rubber feet -
see photo down page.
(2) The turntable proper, which is supported by four suspension pods in the corners.
The only connection between the units
is by the drive belt and the support the turntable sits on.
With my box the main turntable structure sits on the top MDF platform, which rests on the sand
only.
The motor/pulley base rests on the three concrete pillars. The pillars are bolted to the base
of the sandbox and pass through oversized holes to be level with
the top of the MDF plinth.
The box sides and MDF platform are separated by a 15mm strip of loose cell
foam. This gives the top a finished look without compromising isolation and also serves to keep the platform centred.
Cement pillars bolted in - base painted with sealer
Pillars painted black - box filled with sand ready to level
Foam edging
between MDF plinth and box sides - Suspension pods and motor unit in position:
View of finished box - motor pillar bolts can be seen on bottom of box:
To be honest, I set my expectations low. I had recently read on
Vinyl Asylum
that one TNT owner had ditched his Brightstar sand isolation for a lightweight
support. This user said overdamping with the sandbox had reduced clarity, detail
and dynamics. I half expected the box to sound very disappointing.
First record on the platter was Carol Kidd's
'Nice Work' which happened to be sitting on top of the pile.
Immediately I knew I was on a good thing. Vocals were better focused, more
present with greater detail and nuance. The piano was killer, much less smeared
and plummy, with more ambiance and natural decay audible - it plain sounded more
real. I heard no evidence of reduced dynamics, quite the opposite. The
backgrounds were much quieter and dynamics expanded and flourished.
The overdamping idea has got me beat. The effect of this sandbox is to
release a whole raft of low level detail and ambiance cues while reducing blurring and
blunting of sounds. Everything sounds less coloured and more real. So my
experience is the opposite of the user referred to above. I suggest trying a
sandbox to see if it works for you. I consider the sandbox the best 'bang for buck'
(by far!) I've gotten in my system.
Back to Tobes' Audio Page
The total project cost was about $50-60, but some material I already had on-hand.
Braced sandbox with cement pillars
for motor assembly ready to bolt on.
Plinth for the turntable proper in the background, shows holes for the pillars to pass through.
Sound