Strange Antiskate - New Jelco TK-850M

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CSGTT
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Strange Antiskate - New Jelco TK-850M

Post by CSGTT » 22 Oct 2019 20:53

Strange or not? The antiskate seems to have two very different modes: reasonable - nice, slow movement through the runout, or skating uncontrolled onto the label. Doesn't usually seem to happen after the end of recorded grooves, but if the stylus is placed in the runout. Table is level, antiskate is set or varied. It's almost as if antiskate force comes and goes with no consistent relationship to actions.

Placing the stylus on a completely smooth side, whether by armlift or hand, always results in tonearm screaming into the label.

Long ago when I had a Dual "record player" the action of antiskate settings was very predictable. Easy to see the tonearm drift outward with higher setting. On the Jelco I can max out the setting and never see outward movement.

Is there something about the Jelco design I'm missing?

nat
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Re: Strange Antiskate - New Jelco TK-850M

Post by nat » 22 Oct 2019 23:50

Doesn't seem right. I wonder if the problem might be that the arm is not rotated to the right place in its mount. The Jelcos I've had apart used a cam running against a spring loaded lever, and the arm mount was twisted to the point where the cam is out of its appropriate range, you might get a situation where the antiskating was way off.

CSGTT
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Re: Strange Antiskate - New Jelco TK-850M

Post by CSGTT » 23 Oct 2019 04:12

Yes, thanks for that. I'm wondering what I did in installing the arm that might have been done differently. It simply went straight into the mounting base, arm rest at the recessed part pointing to the front. Nothing to be considered that's indicated in the Jelco rather simple instructions. And nothing seemed amiss until setting the arm and stylus onto a blank area. It's almost as though there's something at work other than a simple force to counteract skating. Trying figure out how to disgnose an issue.

After living with a first-gen Well Tempered Arm for 27 years it's so nice to be able to remove the cartridge with headshell, pull the whole arm out of its mount, unplug the interconnect DIN plug, and check things out.

Hugo
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Re: Strange Antiskate - New Jelco TK-850M

Post by Hugo » 23 Oct 2019 06:37

That's unusual - I have found the anti-skating control on the new Jelco arms to be unusually well calibrated, when tested using AnalogMagik, although of course there are a few variables when it comes to setting the appropriate force.

CSGTT
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Re: Strange Antiskate - New Jelco TK-850M

Post by CSGTT » 23 Oct 2019 16:10

The most repeatable symptom is that when allowing the stylus to play the final recorded grooves, the arm moves slowly and normally through the runout and stops just before the label. If I place it with the cueing lever it skates quickly onto the label. What the hell difference is at work here?

CSGTT
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Re: Strange Antiskate - New Jelco TK-850M - Solved (Essentially)

Post by CSGTT » 23 Oct 2019 19:02

I think I've solved the issue. I now see that it's important to orient the arm in its mount so the armrest points to 6 o'clock. I found this out dramatically when I rotated the whole assembly clockwise to allow the cartridge to rest over the spindle to check overhang. In that position the tonearm was essentially non-functional, skipping badly regardless of antiskate setting.

This aspect of installation seems to go unmentioned, certainly in Jelco's own included instructions. It must be critical to the calibration of the antiskate adjustment increments, but it's really clear other than a vague 6 o'clock position. And does the mounting collar's cutout area mean something? The center of it points to around 4:30 or 5:00.

Every time one loosens the grub screw to adjust VTA this baseline rotational position can change, and the antiskate calibration along with it. Seems that there should be an indicator or detent as a guide. Does anyone have thoughts on this?

Sunwire
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Re: Strange Antiskate - New Jelco TK-850M

Post by Sunwire » 23 Oct 2019 19:11

Before testing antiskating on a record, check antiskating with the arm balanced (floating with 0 VTF).

scho2684
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Re: Strange Antiskate - New Jelco TK-850M - Solved (Essentially)

Post by scho2684 » 23 Oct 2019 19:24

CSGTT wrote:
23 Oct 2019 19:02
And does the mounting collar's cutout area mean something? The center of it points to around 4:30 or 5:00.
It means that on tables where the plinth is high in relation to the platter, the bottom of the arm lift has some free space there...

Reading this story twice, I still can't figure out where it goes wrong (or what really had solved it)

CSGTT
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Re: Strange Antiskate - New Jelco TK-850M

Post by CSGTT » 23 Oct 2019 19:52

After intial installation I had the the armrest oriented for convenience, relatively close to the platter, at maybe 7:00. That seems sufficient to throw antiskate well off. Testing it showed it to be wrong, but it was unclear why. I've still not found information on what is formally ideal, and how to maintain that position while changing VTA.

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Re: Strange Antiskate - New Jelco TK-850M

Post by scho2684 » 23 Oct 2019 20:18

Well, my 750D might not act as a perfect example but here's what I'm doing as that armrest has a very convenient shape:
I adjust the orientation in such a way that the end of the armrest always pushes the arm beyond the point where it can fall off the record in case you did not positioned it correct. It has no (visual/audible) effect on my anti skating.

Further more: the orientation of the arm should never ever have such massive effect on the AS setting as is suggested here. Only from SME I know they specify a distance spindle/stylus for arm orientation, Jelco does not...

If you want to maintain orientation, you should use the Easy VTA (use the search option, or google it)
But that is only handy in case you switch a lot of cartridges...

CSGTT
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Re: Strange Antiskate - New Jelco TK-850M

Post by CSGTT » 23 Oct 2019 22:20

Thanks for chiming in to this thread. With my TK-850 it appears that the antiskate has a limited range of accurate effect, something like from the label to a bit off the lead in. And it works properly now. Makes sense to me that a spring-type antiskate mechanism can't cover a very large range, and depends on the point where it needs to take effect. I admit this is all based on my experience with this one arm over less than a week of use. I did have a Sumiko MMT many years ago but never really pushed its capabilities.

I have an Easy VTA gizmo on its way to me now. Should be excellent.

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