-edible zone-

-- Receiving

-- The TD150 mkII Subchassis and Bearing

 

*TD150 brg housing TD150 brg (hint: click thumbnail for full image)

*

-- This part feels stout when held by hand.  The structural integrity seems pretty fair.  However, when put to a deflection under load test of its own platter system, some flexing was seen.   

-- (See test page for the gory details)

*The weight Weight bare chassis with brg. housing: 1 pound 14 ounces.

*TD150 Subchassis

-- Above: bottom view, TD150 mkII subchassis

*Dwg with dimensions

-- Above: Hole location dimensions, in inches, taken from the sample

*TD150 - TD160

-- Above: Overlay, TD160 subchassis over the TD150

*comparison of subchassis (click thumbnail for full size image)

*top side up

*TD160 Brg. Housing

--The TD160 bearing housing appears to be nearly identical to that of the TD150.

*TD160 Brg weight measure 160 weight 2

--Some stats for the TD160 mk II subchassis pictured above:

 

*flexes under the weight Testing the subchassis for deflection under load.  I was curious to see if the subchassis framework would flex under the load of its own platter and armboard.....and, like the TD150 subchassis, it did.

  ________________________________________________horizontal rule 

*Looking at the suspension

  1) TD150 suspension

-- Above photo #1 shows the underside of the table, just prior starting the stage 2 sessions. The object being to set the table up in near stock configuration, align it and then just listen for a few days to get some sense of the deck's signature sound. Springs and rubbers have been cleaned and powdered (talc). An arm board has been cut from 3/8 inch thick grade LE phenolic. The SME 3009 S2i tonearm has been mounted. The suspension has been leveled and tuned for vertical bounce action.

It is at this point that I notice, when looking at this view from underneath, the three very different spring adjustments. It is very clear that the spring nearest the tonearm is taking more weight than the other two springs. In another project, I had weighed this tonearm and compared the weight to the Thorens TP16 tonearm. The SME was heavier by a few ounces. However the TD150 Mk II does not use the TP16. It used the TP13A. I don't know the weight of that arm but assume it must be substantially lighter.

 2) TD150 subchassis dimensions

-- Above illustration #2. A cad drawing of the subchassis that shows the spring locations relative to the spindle bearing. It appears that the two arm board springs are located closer to the bearing than the far spring. I think this spacing will result in an uneven spring loading even when the standard arm and board is being carried.

-- In spite of the uneven spring loading, it is possible to get a "mainly" vertical bounce action with careful tuning of the springs, their height adjustment and by centering the spring around the stud that holds it. However, it isn't possible to get a true "piston" action. Instead, the bounce action of the armboard and platter may be observed as relatively even but with some difference in timing. The tonearm end will crest just slightly behind the unloaded end of the arm board. The platter crests at a slightly different time. This results in a slight jiggle. The jiggle can be reduced substantially thru careful tuning as described above, but not completely eliminated.

-- My take is that a true up/down piston action will not occur until the mass of the suspended elements is centered between the three springs. I can think of two ways to achieve this.

1) The first, and easiest, is to fix additional weights to the subchassis next to 2 of the lighter loaded springs. The object being to load each of the three springs with equal weight.

2) The second, and more elaborate, would not only balance the weight load between the three springs, but place the mass center lower within the vertical dimensions of the box. I can envision this as a second frame attached under the upper existing frame. Provision could be made for a moveable weight to help find a precise mass center. The lower the center of gravity, the more control will be had over bounce action. Do this right and the under frame could also serve to stiffen the upper frame.

-- However, I'm thinking ahead. I have seen similar spring loading issues when tuning my TD160. The spring nearest the arm board seems to be taking a heavier load. I feel that this may be inherent in the design. Call it a weakness of the table. We have already seen another weakness with regard to subchassis rigidity. I will accept the above limitation for the time being, but down the road, if significant sonic improvements are to be achieved, a re-design of the subchassis needs to be done so that each of the three springs are loaded equally and that the mass center is as low as is possible within the confines of the cabinet interior.  

 

-- Clean-up and prep

-- Step 2: Play and listen before the upgrades

-- Early listening impressions.

-- Sited on a wall shelf and spinning some Freddy Hubbard. I have one of Ken Lyon's Neuance shelves under it. I used the Neuance with the TD160 in this same location just prior to obtaining the TD150.

-- Early Listening:

-- The area foot print of this deck is smaller than that of its successor, the TD160. In the vertical, cabinet height is also smaller. What isn't smaller is the sound this little turntable can produce. Compared to the TD160, the overall sonic picture seems slightly brighter. Highs are less rolled off. The Shure V15VxMR is a factor here, but I've used the same arm, cart and phono stage combo on both tables. Comparisons are valid. Dynamics seem good. Attack, sustain and decay qualities are slightly sharper in attack, clean and unwavering in sustain and then about the same in decay. Detail levels are also good for the cartridge, arm and phono stage combination in use. There is a good, if not better, sense of timbre and texture. And this is with a nearly stock table...! The arm is the SME 3009 S2 improved with fixed headshell.

-- The SME tonearm mounts near the extremes of the armboard. This was also the case when fitting the same arm to the TD160 but the larger, open armboard area of the TD150 makes tonearm mounting infinitely more simple. Once fitted operation is quite good. Cueing operation was convenient and stable.

-- The motor:  I don't think it is accurate to say that the TD160 and TD150 share the same motor. Yes, they are both 16-pole AC synchronous motors. That much they have in common. The shape of the TD150 motor housing appears identical to that of the TD125 (first version). This is quite different from the TD16x series motors which have a triangular shaped case work. The motor drive pulley is lathe turned from solid aluminum. With the TD16x series you get a plastic injection molded clutch pulley. I'm not saying that is bad, it is just what you get. The motor torque is quite low on this TD150. With belt off and motor spinning at 33-1/3, I can lightly pinch the pulley between thumb and forefinger and thus stop the motor from spinning. Easily. I checked to make sure if there was any slippage between pulley and the motor shaft by marking the shaft and pulley. No slip. This motor just has very little torque. Listening to music my ears tell me this must be good.

-- The platter bearing:

-- I have already determined the spindle shaft and bushings to be in excellent, unworn condition. I put some fresh 20 wt. oil into the bearing housing well, then placed the spindle shaft, with inner platter attached, into the bearing housing and let it slide down to the pool of oil. The shaft floats on top of the oil at first then, slowly, the lube passes by the narrow clearance between bushing and shaft and allows the spindle bearing tip to reach home against the thrust plate. When I get some excess oil overflowing out of the bearing housing I know I have enough lube in there for the upper bushing to stay bathed in oil.

-- The footers and bottom cover:

-- This deck came without a bottom cover as well. Naturally I was going to replace that too. The footers I found on the deck are the simple but thick and solid rubber furniture feet that have a self adhesive side and have been stuck to the four corner braces within the cabinet directly over the mounting holes for the standard feet. While kind of cheesy, these feet do not suffer from any lack of solidness. I will replace these when the new cabinet with new bottom cover is fabricated. They'll work for the time being.

I bought the deck without armboard or arm. I provide both. For armboard material I am using 3/8 inch thick grade LE canvas /phenolic as the base material and then a smaller piece of 1/8th inch thick carbon fiber to mount the arm to. This results in a very stiff platform to hold the arm. Enough with the explanations. I'll just listen to this little table for a day or two before going to the next step. It's a good one...!

-- Thinking About Springs

 

 * 3d subchassis

-- Above: the standard TD150 frame 3d cad dwg. drawn by site owner.

-- Data for the standard Thorens TD150 spring:

 

 -- More notes:

-- The three springs carry the tonearm, which has an arm/cartridge natural resonance of between 8 to 12 hz, This is an industry standard but may vary outside this range if arm and cartridge are not well matched.

-- Footfall resonance is, around the web, popularly thought to be approximately 3 hz but will not be an issue as the turntable can be mounted from the wall.

-- Even more notes about springs:

-- Spring stiffness is expressed in terms of how much force is needed to compress a spring one inch. If a spring is rated at 4 lbs, this means that it takes 4 lbs of pressure to deflect the spring one inch.

-- Static deflection is the amount of distance the spring is compressed when under a normal load and at rest.

-- Natural frequency is the number of oscillations a spring will go through under a given load.

-- Some formulas for calculating natural frequency:

 
-- NF = 3.13 SQRT K/load
-- or
-- NF = 3.13 / sqrt DST (in inches)
-- or
-- NF = 5 sqrt 1/DST (in cm)

-- The natural frequency of the sprung suspension should exist between foot fall and the cart/arm natural frequency. If foot fall is approximately 3 hz and the low end of cart/arm frequency is 8 hz, then the target for spring frequency is 4 - 6 hz.

-- But.....Does it have to be Springs?

-- Hmmm. Tired of calculating spring rates, natural frequencies...? Tired of periodic suspension tuning...?

-- I thought I would try an 'isolator grommet' rather than a spring just to see how it sounds. These grommets do isolate between the subchassis and the motor plate. I suppose it could still be called a suspended design because the subchassis is carried by the grommets.

*Heater Hose Left: the "heater hose" isolator.

-- The above idea uses a pair of the large Thorens rubber spring grommets and a length of automotive heater hose cut square and then fitted in between at the three spring locations. I calculate the natural frequency of this spring to be less than, ummmm 1 hz....;-) OK, it doesn't oscillate at all. Stethoscope listening suggests that motor vibes aren't getting into the subchassis plate this way.

-- Ok, so I've played some vinyl in this configuration and have noticed a background noise level comparable to that of a 'spring equipped' TD150.... or maybe the 'sprung' TT actually does have a quieter noise floor.  But with the heater-hose mod the sense of timing and articulation of detail seemed perhaps a tad sharper. 

-- Who says the isolation has to be by way of springs anyway....? But what about acoustic feedback? The sprung suspension does offer at least some isolation from airborne sound waves.

-- Note: I tried this for a while and after some considerable time went back to the original subchassis and spring setup. Bass was a bit better with springs. I have tried different conical coil springs. At one time a set of Linn LP12 springs. Those were far stiffer than the oem Thorens TD150 springs. I'm not ready to say which spring was preferable. The stiffer Linn springs were less affected by foot fall in that room with the flexy flooring and when not siting the turntable to a wall shelf. Something I do from time to time.