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Re: Oh My God, What Have I done!?
Posted: Fri Nov 25, 2022 10:48 pm
by slinger
Re: Oh My God, What Have I done!?
Posted: Fri Nov 25, 2022 11:02 pm
by Geoff.R.G
CN211276 wrote: ↑Fri Nov 25, 2022 10:28 pm
Vinyl-ant wrote: ↑Fri Nov 25, 2022 9:16 pm
The fact that it went off after a week
This might well explain why I was so unimpressed at the demo, as has been put forward by someone in the trade who used to post here some time back.
What would I want to do with a deck that goes out of tune every time a fly lands on it and farts.
I have always been intrigued by this “going out of tune” of the LP12. I can’t see that there is anything to go out of tune! The settings of the arm shouldn’t change, assuming the adjustments were made correctly and suitably tightened. It isn’t as though there are significant mechanical loads on the bearings or cartridge mounting screws. There are no unexpected vibrations at resonant frequencies, unless they are deliberately excited. Does the drive belt go out of tune? Does the suspension drift?
If a turntable needs regular adjustable to keep it performing properly I would suspect poor engineering. We used to set up the convergence of video projectors on 747s and expect them to stay pretty much correct for hundreds of hours of being bounced around the sky. Of course if you design the adjustment mechanism without any means of locking it then it will drift but it usually requires a degree of mechanical abuse. Is the design of the LP12 such that adjustments drift in normal use? If so I would be applying locktite or looking to modify it to prevent drift.
Can anyone tell me what it is that needs regular attention?
Re: Oh My God, What Have I done!?
Posted: Fri Nov 25, 2022 11:16 pm
by CN211276
Geoff.R.G wrote: ↑Fri Nov 25, 2022 11:02 pm
Can anyone tell me what it is that needs regular attention?
I think there is something in the archive about this, probably posted by Richard. I believe It is to do with a suspension design flaw. Ivor, or more accurately Hamish Robinson, got it wrong.
Re: Oh My God, What Have I done!?
Posted: Fri Nov 25, 2022 11:19 pm
by TheRealAleman
Re: Oh My God, What Have I done!?
Posted: Fri Nov 25, 2022 11:49 pm
by Vinyl-ant
The suspension itself sits on 3 bolts which hang down from the stainless top plate, there are nuts and washers and rubber bushes that retain the springs which are adjusted to get the subchassis to balance. The aim is to have the arm board square in its cutout and flush with the top face of the plinth and top plate. With the belt on, when gently tapped at the record spindle the deck should bounce straight up and down a couple of times withouth a 'shimmy' for want of a better word. The arm cable forms a part of the suspension as it has to be dressed properly into a p clip on the plinth, not impede suspension movement, but also prevent the subchassis from twisting when power is applied to the motor. When switched on you will see the deck do a little dance where the subchassis moves around under the initial torque from the motor starting up and the platter getting up to speed, then goes back to sitting where it should do. The arm cable being fixed to the plinth is supposed to stop the subchassis from twisting clockwise under the torque load from the motor. Get this bit wrong and the suspension movement is impeded so the bounce ends up all over the place and it shimmies, and the constant twisting force applied to the subchassis loosens the adjuster nuts. A little dab of superglue mostly sorts the adjuster nut problem, but flexing of the arm cable as the chassis moves under load causes it to move fractionally and after a while cocks up the suspension adjustment. My project arm didnt have a cable, it had bare wires that were soldered to a tag strip which was screwed into the plinth. So it didnt do anything at all to the suspension setup. It didnt stop the chassis twist on startup at all, but it was fairly negligible anyway. It was however enough to subtly affect the suspension adjuster nuts. I used to check the arm board was still flush with the top of the plinth with a straight edge every so often when i thought it sounded a little off and there was usually a slight deviation. It was worse when the deck was on a unit on the floor because people walking by it would make it jump about which sped up the process of it going out of adjustment, ham fisted cuing or knocking it would also speed this up. Wasnt as bad when it was on a wall shelf.
When the thing went out of tune it was subtle but noticable
Re: Oh My God, What Have I done!?
Posted: Fri Nov 25, 2022 11:56 pm
by Geoff.R.G
Vinyl-ant wrote: ↑Fri Nov 25, 2022 11:49 pm
The suspension itself sits on 3 bolts which hang down from the stainless top plate, there are nuts and washers and rubber bushes that retain the springs which are adjusted to get the subchassis to balance. The aim is to have the arm board square in its cutout and flush with the top face of the plinth and top plate. With the belt on, when gently tapped at the record spindle the deck should bounce straight up and down a couple of times withouth a 'shimmy' for want of a better word. The arm cable forms a part of the suspension as it has to be dressed properly into a p clip on the plinth, not impede suspension movement, but also prevent the subchassis from twisting when power is applied to the motor. When switched on you will see the deck do a little dance where the subchassis moves around under the initial torque from the motor starting up and the platter getting up to speed, then goes back to sitting where it should do. The arm cable being fixed to the plinth is supposed to stop the subchassis from twisting clockwise under the torque load from the motor. Get this bit wrong and the suspension movement is impeded so the bounce ends up all over the place and it shimmies, and the constant twisting force applied to the subchassis loosens the adjuster nuts. A little dab of superglue mostly sorts the adjuster nut problem, but flexing of the arm cable as the chassis moves under load causes it to move fractionally and after a while cocks up the suspension adjustment. My project arm didnt have a cable, it had bare wires that were soldered to a tag strip which was screwed into the plinth. So it didnt do anything at all to the suspension setup. It didnt stop the chassis twist on startup at all, but it was fairly negligible anyway. It was however enough to subtly affect the suspension adjuster nuts. I used to check the arm board was still flush with the top of the plinth with a straight edge every so often when i thought it sounded a little off and there was usually a slight deviation. It was worse when the deck was on a unit on the floor because people walking by it would make it jump about which sped up the process of it going out of adjustment, ham fisted cuing or knocking it would also speed this up. Wasnt as bad when it was on a wall shelf.
When the thing went out of tune it was subtle but noticable
So it’s just poor engineering then?
Re: Oh My God, What Have I done!?
Posted: Sat Nov 26, 2022 12:02 am
by Vinyl-ant
we are talking about a 1987 vintage valhalla lp12, with a pressed steel subchassis. This had the wanky mdf arm board secured with poxy little woodscrews and the incredibly stiff old grey linn arm cable. The modern ones with the solid subchassis and arm board and modern arm cable may not have the same issues as the 80s and 90s variants.
Engineering? Lets just say i was rather disappointed when i looked inside that one
My 1985 xerxes is better engineered. But has its own game breaking issues. At least the lp12 didnt eventually brick itself by either its psu cooking itself or its top plate sagging so badly it couldnt rotate.
80s british turntables more complicated than a rega or a revolver rebel, on the whole, were not very well built..... ime obviously...
Re: Oh My God, What Have I done!?
Posted: Sat Nov 26, 2022 7:32 am
by karatestu
I don't suppose the thin bendy top plate helps much either. Because of that the three suspension bolts don't sit vertically. So then you have to bend the bolts with one of those kinky tools.
When fitting a Naim prefix internal phonostage there is no arm cable to prevent the twisting, I think I read that in this case some users resorted to taping cotton thread between the plinth and subchassis to stop the twisting
Sounds like my kind of bodge
Re: Oh My God, What Have I done!?
Posted: Sat Nov 26, 2022 10:02 am
by Latteman
The only ‘British’ suspension TT I had that was easy to live with was the Systemdek.
The less complex design of the funk firm vector was hugely let down by the minimalist speed controller- I had a townshend Avalon & Rock mk2- what a pita the trough was- I can’t remember if I liked the sound or was it just the aesthetics
Give me a re plinthed Lenco or 70’s Japanese DD any day
(I do like the sound of a good belt drive- they do have a beguiling quality- unfortunately most of those are diy and not really available on the market)
Re: Oh My God, What Have I done!?
Posted: Sat Nov 26, 2022 10:51 am
by Geoff.R.G
The premise that a suspension is needed to eliminate feedback is, of course, flawed. At normal, domestic, listening levels it is extremely difficult to induce feedback in a record playing system, even when done deliberately. A turntable on a cabinet sitting on a suspended wooden floor may benefit from some springs to isolate the assembly from the floor but a solid shelf attached to a brick wall is a better solution.
My first record player was a BSR auto changer, I was probably about 10 at the time. Essentially it was very similar to a Lenco with the chassis sitting on springs to provide some isolation from the speaker in the same cabinet. The next was a Pioneer PL12D, a similar idea but with a belt drive. Only later did I progress to a suspended turntable, a Thorens TD160, which I still have. The point being that in the intervening 50+ years I have never encountered a problem with feedback. Sure I have heard plenty of it in audio systems involving microphones but never in a turntable, irrespective of the construction.
I suspect that replacing the springs in a Linn LP12 with solid spacers and sitting the plinth on isolating feet would solve the “going out of tune” problem permanently. As I see it, the suspension is a solution to a problem that, for 99.99% of users, doesn’t exist.
The Thorens doesn’t need regular adjustments, in that respect it is fit and forget.