Geo Disc sight-line issues

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RobberOfBostonPlace
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Geo Disc sight-line issues

Post by RobberOfBostonPlace » 21 Jul 2019 03:39

So I have a Fluance RT-85 with the Ortofon 2M Blue cartridge, and I'm using the Geo Disc to align this cartridge. I am having an incredibly hard time locating the tonearm pivot point so that I can correctly position the Geo Disc. Has anyone had any success with the Geo Disc and finding the tonearm pivot point for this turntable?

Agrippa
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Re: Geo Disc sight-line issues

Post by Agrippa » 21 Jul 2019 05:56

It really doesn't have to be micrometer precise, as the GeoDisc is never going to get you perfect precision anyway. Best possible estimate will do just fine. If you absolutely need absolute exactitude the GeoDisc is very much the wrong tool and you need something like a MintLP or Feickert protractor instead.

Don't get me wrong, the GeoDisc is a perfectly excellent tool and I own and used one myself for many years. It just isn't at all suitable for people who worry about the tiniest details of cartridge alignment.

Legrace
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Re: Geo Disc sight-line issues

Post by Legrace » 21 Jul 2019 10:40

Not surprised, the sight line feature on the geodisc is horribly unreliable, a guessing game at best. A simple mod though will reduce potential for error considerably. Simply attach a string along the top edge of the sight line, long enough to reach over to the pivot point. Place the string over the pivot point then sight back along the line and adjust the geodisc until the line is perfectly straight. Then apply tape to edge of platter so it doesn't shift on you. Now set the cartridge. Ever since I have always had good results using it.

Agrippa
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Re: Geo Disc sight-line issues

Post by Agrippa » 21 Jul 2019 11:02

Though it is unquestionably imprecise, I always got good results with the GeoDisc. Admittedly I get even better results with the MintLP protractor I've been using for a number of years now, but there's certainly not a night and day difference. After all, VTA/SRA and azimuth have a vastly greater impact on sound quality than any slight aberration in alignment geometry.

RobberOfBostonPlace
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Re: Geo Disc sight-line issues

Post by RobberOfBostonPlace » 21 Jul 2019 12:07

Agrippa wrote:
21 Jul 2019 05:56
It really doesn't have to be micrometer precise, as the GeoDisc is never going to get you perfect precision anyway. Best possible estimate will do just fine. If you absolutely need absolute exactitude the GeoDisc is very much the wrong tool and you need something like a MintLP or Feickert protractor instead.

Don't get me wrong, the GeoDisc is a perfectly excellent tool and I own and used one myself for many years. It just isn't at all suitable for people who worry about the tiniest details of cartridge alignment.
I have the Feickert and have a difficult time with that as well, locating the pivot point is a pain.

Agrippa
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Re: Geo Disc sight-line issues

Post by Agrippa » 21 Jul 2019 13:24

I'm entirely unfamiliar with the Fluance RT-85, but having googled it I can't really see where the difficulty lies. Looking at this picture and assuming yours is identical, it seems to me that it would be quite easy to determine the pivot point with quite some accuracy.
index.jpg
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RobberOfBostonPlace
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Re: Geo Disc sight-line issues

Post by RobberOfBostonPlace » 21 Jul 2019 14:03

Agrippa wrote:
21 Jul 2019 13:24
I'm entirely unfamiliar with the Fluance RT-85, but having googled it I can't really see where the difficulty lies. Looking at this picture and assuming yours is identical, it seems to me that it would be quite easy to determine the pivot point with quite some accuracy.

index.jpg
The pivot to spindle distance for the Fluance RT-85 is supposedly 204.8, but when I use the Feickert and set it to 204.8 it doesn't go anywhere near the middle of what you've shown in the picture. There lies my issue.

theclosetguy
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Re: Geo Disc sight-line issues

Post by theclosetguy » 21 Jul 2019 15:52

According to the Fluance website the effective tonearm length for your table/arm is 224mm Overhang is 19.2 mm so yes 204.8 mm. I'd pull out a tape measure and confirm that distance. if its correct, I'd chuck the GeoDisc. I had one, tossed it years ago.
Mike M

Agrippa
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Re: Geo Disc sight-line issues

Post by Agrippa » 21 Jul 2019 23:52

RobberOfBostonPlace wrote:
21 Jul 2019 14:03
The pivot to spindle distance for the Fluance RT-85 is supposedly 204.8, but when I use the Feickert and set it to 204.8 it doesn't go anywhere near the middle of what you've shown in the picture. There lies my issue.
In which case the issue appears to be faulty and misleading specs rather than a pivot point that is hard to locate. If 204.8 is indeed the correct mounting distance of the arm and the distance to the centre point is different, then the arm must be mounted incorrectly. That being the case the only solution appears to be to re-mount the arm at the correct distance.

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Re: Geo Disc sight-line issues

Post by theclosetguy » 22 Jul 2019 15:59

So Agrippa
Are you suggesting the Manufacturer mounted the arms wrong? Or maybe the Manufacture does not want us to know the true spec's

Agrippa
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Re: Geo Disc sight-line issues

Post by Agrippa » 23 Jul 2019 00:37

I haven't got the foggiest notion to be honest and I've never heard of anything similar before. I would suggest a mail to the dealer/manufacturer with a request for an explanation.

nat
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Re: Geo Disc sight-line issues

Post by nat » 24 Jul 2019 01:19

Not to trot out all the old tired excuses, but is it possible that the real issue is different alignments?
There are three common alignments (Bauerwald, Lofgren, and Stevenson), but some manufacturers and users use different ones. If you try to align an arm with a different alignment than intended, you can certainly do it, and it will sound fine, but it won't be neatly placed in the headshell - it will be skewed and probably at the very limit of the adjustment range. I think for a lot of people the very marginal improvement in sound that comes from one alignment or the other (and assuming the alignment was done perfectly, which we all know isn't exactly a safe assumption), isn't worth the stab in the eye every time you look at the arm.
I'd go back to whatever alignment protractor that Fluance provided, and see if that works and sounds good.

Sunwire
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Re: Geo Disc sight-line issues

Post by Sunwire » 24 Jul 2019 05:25

Legrace wrote:
21 Jul 2019 10:40
. . . Simply attach a string along the top edge of the sight line, long enough to reach over to the pivot point. Place the string over the pivot point then sight back along the line and adjust the geodisc until the line is perfectly straight. Then apply tape to edge of platter so it doesn't shift on you. . . .
This is the best advice.

I did a quick search for "Geo Disc" in the forum here. There were quite a few results.
I didn't read a lot of the threads, but another user recommended a similar method with string to align the sight line with the tonearm pivot.
I can imagine a couple of different ways this might be done.
As long as the string, sight line, and tonearm pivot are all aligned, it should work fine.
Searching the forum for "Geo Disc" may turn up other helpful tips.

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