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Pinging John Elison....

24.117.206.83
Posted on May 20, 2013 at 07:41:04
AudioSoul
Audiophile

Posts: 4594
Location: north central AZ
Joined: July 9, 2005
Hi John, I have a question. I ordered a Jelco SA-370H tonearm from Ebay. I have not received it yet but I am doing some preliminary research. I went on Vinylengine and got the specs for this arm. And I know you mounted one to a Kenwood KD-500. The spec sheet gives 239mm effective length. Is that the same as spindle to pivot distance? If not what measurement did you use to mount the arm? Thanks for any info you can give me....

 

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RE: Pinging John Elison...., posted on May 20, 2013 at 11:35:53
John Elison
Audiophile

Posts: 23900
Location: Central Kentucky
Joined: December 20, 2000
Contributor
  Since: January 29, 2004
 No, effective length is always stylus-to-pivot distance. Spindle-to-pivot mounting distance depends on your choice of null-points. If you intend to use null-point radii of 66-mm and 120.9-mm, spindle-to-pivot mounting distance would be:

Sqrt[2392 - (66 x 120.9)] = 221.68-mm

The Jelco SA-370H can be used as a drop-in replacement for Rega tonearms, which have a spindle-to-pivot mounting distance of 222-mm. However, it is designed for a Löfgren A alignment instead of Rega's alignment.

Best regards,
John Elison

 

No. Pivot to spindle is effective length minus overhang., posted on May 20, 2013 at 11:55:37
Opus 104
 In the case of the 370, that's 239 - 17 = 222 mm, the standard Rega spec.

 

RE: Pinging John Elison...., posted on May 20, 2013 at 17:47:49
AudioSoul
Audiophile

Posts: 4594
Location: north central AZ
Joined: July 9, 2005
Are you guys sure about that? On the drawing (not to scale) the 239mm measurement is from the center of the arm to just a few mm short of the end of the headshell. If it is 222mm, how do you measure for the null points? Any time I have mounted a arm I just go by the spindle to arm center. Thanks for your help guys....

 

Check this 2008 post by Opus 104, posted on May 20, 2013 at 18:16:43
1973shovel
Audiophile

Posts: 10117
Location: Greenville SC
Joined: February 25, 2007
 The Jelco drawing clearly shows the "Pivot to turntable cntr." (which is spindle center to arm center) at 222mm.

Be certain you measure from the center of the spindle, and not the edge.

Good luck with it.

 

RE: Pinging John Elison...., posted on May 20, 2013 at 19:04:18
John Elison
Audiophile

Posts: 23900
Location: Central Kentucky
Joined: December 20, 2000
Contributor
  Since: January 29, 2004
 Don't know what more I can tell you.

Effective length of the Jelco SA-370H is 239-mm and mounting distance is 221.68-mm. You achieve the alignment null-points using an alignment protractor designed for Löfgren A null radii of 66-mm and 120.9-mm.

> how do you measure for the null points?

The alignment null-points are the two points on the record playing surface where the tonearm is in true alignment with the tangent to the groove at the stylus. These points are measured from the center of the spindle along the arc the stylus travels. The inner null-point is 66-mm from the center of the platter spindle and the outer null-point is 120.9-mm from the center of the platter spindle.

If you need an alignment protractor, you can print your own from Conrad Hoffman's custom arc template generator for phono cartridge alignment. Just specify the mounting distance as 221.68-mm and use the IEC inner and outer groove radii of 60.325-mm and 146.05-mm. If you want to buy an excellent arc protractor, check out the link below for the Ken Willis AccuTrak Protractor. Ken Willis makes an excellent arc protractor for a reasonable and fair price.

Best regards,
John Elison


 

RE: Check this 2008 post by Opus 104, posted on May 20, 2013 at 23:34:15
John Elison
Audiophile

Posts: 23900
Location: Central Kentucky
Joined: December 20, 2000
Contributor
  Since: January 29, 2004
 A mounting distance of 222-mm is just fine. It means that effective length will actually be 239.3-mm when aligned for null-points of 66-mm and 120.9-mm. Overhang will be 17.3-mm.

Effective Length = Sqrt[2222 + (66 x 120.9)] = 239.3-mm

Best regards,
John Elison

 

I just checked the dimensions marked on my WallyTractor, posted on May 21, 2013 at 08:34:06
1973shovel
Audiophile

Posts: 10117
Location: Greenville SC
Joined: February 25, 2007
 Made for Rega arms. They are:

Effective Length: 239 mm

Pivot to Spindle Distance: 221.7

Overhang: (B) 17.3 mm (L) 17.8 mm



 

RE: I just checked the dimensions marked on my WallyTractor, posted on May 21, 2013 at 12:07:25
John Elison
Audiophile

Posts: 23900
Location: Central Kentucky
Joined: December 20, 2000
Contributor
  Since: January 29, 2004
 That's a perfect protractor for the Jelco SA-370H. I would recommend using the (B) overhang of 17.3-mm. It stands for Baerwald, which we now call Löfgren A. The other overhang of 17.8-mm labeled (L) is for Löfgren B with alignment null-points of 70.3-mm and 116.6-mm. It just goes to show the importance of overhang. Without the slightest change in linear offset, a difference of just 0.5-mm in overhang will change the alignment null-points from 66-mm and 120.9-mm to 70.3-mm and 116.6-mm.

Best regards,
John Elison

 

Thanks John, posted on May 21, 2013 at 20:43:53
1973shovel
Audiophile

Posts: 10117
Location: Greenville SC
Joined: February 25, 2007
 Now I just have to get around to refurbing my Technics SL-110 and actually mounting the Jelco. It's only been five years.

Too many projects, too little time. Work still gets in the way of my play. When I do get some time off, I listen to music instead of soldering, etc.

Perhaps someday, when I finally retire.

 

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