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Thorens 150 Mk II Rt. Front Spring Tuning?

plbeard

plbeard

Active Member
I recently got a Thorens 150 MK II, excellent condition. I don't think it had ever been serviced or tuned; the red paint on the suspension bolts seemed original when I took the back off. Because the platter-chassis was touching the case on the rebound, I tuned the suspension springs. I note that with the belt off, all of the springs have a decent vertical bounce. No matter how I tune them, though, once the belt is on, the spring nearest the headshell of the tone-arm (right front, in a view of the turntable in normal operation) is torqued a bit toward the center of the platter and no longer bounces in a free, up-down manner. I am dubious new springs would do anything here, as they all seem fine. The springs are also in clean, nice shape, so that classic 150 "rehab" page involving gloved-hands prayer and baby powder seems redundant here. Could other 150 Mk II owners who have tuned these springs reflect their experience of that right front spring to me? How does one keep it from being tugged (by the belt) out of a free bounce? Is this the nature of the beast? I have to say that as the TT is tuned now, it sounds great (the stylus' azimuth is spot on, somehow) and spins at 33.33 rpm. But that tonearm base panel is not bouncing ideally, I am sure, due to that right front spring.
 
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I re-iterate my first question: the right front spring on the 150 can be made vertically free-bouncing? Somebody can report that? I'll read the LP12 document, thanks. I am well-familiar with the analogdept doc--it means well, but it has so many ritual instructions for glove-donning and shaking things in bags of baby powder that I found it tedious and not always scientific, but 20% of it, the actual mechanism-related part, is very useful. Are there common benchmarks for the tension points of each spring? I have never seen such mention but that could be very useful starting-point info to avoid a lot of haphazard, trial-and-error work. I know each table is somewhat idiosyncratic, but given the springs and the belt being standardized, there should be +/- 10% certain benchmarks for the tension points of each spring. Can anybody recommend them?
 
The starting point is to level the base and the platter. After that, it is, as you say, "a lot of haphazard, trial-and-error work" and "tedious." There are no shortcuts.

The springs and the belt are far from standardized and you will see that the Cymbiosis guide recommends to keep several extra springs at hand (even with brand new springs of better quality than were ever fitted to a TD-150). Most of us have only the three springs to work with so we're already at a disadvantage. If you want perfection, be prepared to spend hours swapping the springs around and rotating them. You also need to make sure the studs are vertical to begin with, and that's not as easy as it sounds. Linn pros use a long bending tool with a bubble level because you can't just assume the studs are vertical when they're at 90 degrees to the top plate. The TD-150 isn't built quite the same way but the principle applies.
 
I don't see why the studs would not be level if they are square to the top plate and the plate is level. Seems being square to the plate would be way more important than level anyway. Being off-square, the spring force would not be perfectly vertical and you'd be biasing the plate in whatever direction.
 
gadget73 said:
I don't see why the studs would not be level if they are square to the top plate and the plate is level.
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You're assuming that the top plate is an even plane. One of the dirty little secrets of the TD-150 (and LP12) top plate is that it actually takes on a slight curve along the (unsupported) right edge.

gadget73 said:
Seems being square to the plate would be way more important than level anyway. Being off-square, the spring force would not be perfectly vertical and you'd be biasing the plate in whatever direction.
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Sorry, I can't follow you here. The subchassis doesn't "know" if the base is level or not, but if the three studs are not parallel and vertical (plumb) in an absolute sense, it won't bounce straight up and down.
 
When you say "top plate" do you mean the tonearm platform (to which two of the three TD-150 springs are attached) or the literal floor of the rest of the cabinet?
 
bang4buck said:
You're assuming that the top plate is an even plane. One of the dirty little secrets of the TD-150 (and LP12) top plate is that it actually takes on a slight curve along the (unsupported) right edge.
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I have had five TD 150 turntables and currently have two and none had a slight curve. Absolutely no light leak when back lighted with a steel straight edge. No support is needed on the right side as it has a 90 degree bend that is more than adequate to keep the plate straight and level. If there is any little dirty secret, it is that someone has abused the top plate. However, yes it is important that the spring studs are square to the sub chassis.
 
plbeard said:
Is this the nature of the beast?
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Yes. That spring has less weight on it and will react differently than the rear one that supports the weight of the tonearm. This can also get worse if a heavier tonearm is swapped in. However, check to see that you don't have a cheap belt. Some are shorter and some are thicker, both adding to excess pull on the platter chassis.
 
The top plate is the steel plate that carries the three spring studs. You normally don't see it because Thorens applied a beauty cover over it which is just a thin aluminum sheet held on with double-sided tape. On an LP12, the steel is visible. They did away with the aluminum because the screw heads are all hidden under the platter.
 
bang4buck said:
The top plate is the steel plate that carries the three spring studs. You normally don't see it because Thorens applied a beauty cover over it which is just a thin aluminum sheet held on with double-sided tape.
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I think we all know that. I service and check all my TTs by complete disassembly. It is easy to check flatness. Actually a TD 125 has more issues with their die cast aluminum top chassis.

The spring studs would have to be seriously bent to have any significant impact on spring action. If someone is out for perfection then fine. But going to extent that some do is more for entertainment.
 
I was responding to the OP, post #7 above. Apparently we don't all know.

plbeard said:
When you say "top plate" do you mean the tonearm platform (to which two of the three TD-150 springs are attached) or the literal floor of the rest of the cabinet?
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bang4buck said:
I was responding to the OP, post #7 above. Apparently we don't all know.
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Sorry. You didn't quote him so i thought you were responding to the post before yours. But I would like to add that a proven method not used by many is to weigh the spring points on the sub-chassis with the platter, mat, record and tonearm in place. Then add weight to the two light points to match that of the heaviest point. That is the only way to achieve uniform spring action at all three points.
 
John Berard said:
I have had five TD 150 turntables and currently have two and none had a slight curve. Absolutely no light leak when back lighted with a steel straight edge. No support is needed on the right side as it has a 90 degree bend that is more than adequate to keep the plate straight and level. If there is any little dirty secret, it is that someone has abused the top plate. However, yes it is important that the spring studs are square to the sub chassis.
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You're right, sorry, it's been too long since I had the Thorens apart. I forgot about the 90 degree edge. LP12s don't have that and they absolutely do sag along that edge.

Edited to add linked photo showing the sag on a factory fresh LP12.
20190110raw13742-lo.jpg
 
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[QUOTE="bang4buck, post: 13542315, member: 232319"

Edited to add linked photo showing the sag on a factory fresh LP12.
20190110raw13742-lo.jpg
[/QUOTE]

Yes, contrary to some people's belief, the LP12 can be inferior to a Thorens in some ways. But they will never admit it.
 
@plbeard - Sorry, I derailed the thread a little with my mix-up. The curved top plate issue shouldn’t affect you. But do make sure the three studs are straight and plumb.

It’s also important to remember that the subchassis doesn’t hang from the springs, it stands on them. That’s why it doesn’t straighten itself out under gravity, like a properly designed TT does :-)
 
You mentioned having the T. Bailey instructions from Steve's site. Do you also have those authored by Joel Boutreux, a former employee of Thorens? If not you can find them in the Thorens forum at Vinyl Engine, in the "Thorens Overhaul Guide" thread. Regardless of which instructions you follow you'll need to be able to adjust everything from beneath the 'table, and ensure that the plinth is level before doing anything else.

Essentially Joel's instructions are to first make sure the end of each spring's base points to the platter bearing. This will avoid trial and error playing with rotating the springs later. Then, with the belt on, and with your platter mat on the platter, and an LP on the mat, adjust the three springs so that the bottom of the platter is about 6 mm above the decorative metal top plate of the 'table, and the platter is level from left to right and front to back. This should also result in the tonearm board being centered in its opening. If not, start over again with first making sure the end of the spring bases are pointing directly toward the platter bearing. Final test - when pushing straight down on the spindle and releasing, the assembly should swing freely in a piston fashion, straight up and down with no horizontal motion, for several seconds.
 
That sounds like a useful summary; thanks. When I get into this 150 again, I will report back. I complicated my first effort by trying to tune the springs largely (not entirely) with the belt off. My incentive to "fix it" is mixed, because while the tone-arm board is not properly suspended, due to that oddly torqued right-front spring, the stylus is nicely set, the table spins at correct speed, and it sounds great. However, I'd like to see this crazy suspension behave according to spec. The headshell end of the tone-arm board has a fair amount of friction and doesn't bounce well at all.
 
bang4buck said:
Sorry, I can't follow you here. The subchassis doesn't "know" if the base is level or not, but if the three studs are not parallel and vertical (plumb) in an absolute sense, it won't bounce straight up and down.
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that was a comment about bending the spring mounts around so the studs are level. The top plate needs to be level horizontally, and the studs need to be square (90 degrees) to that plate so you get a vertical bounce. Bending the studs so they are level independent of the top plate doesn't make any sense to me. If the studs are not square to the plate, you'd get a non-vertical spring force.
 
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