RE: 9" Jelco 750D tonearm alignment

Posted by flood2 (A) on February 2, 2017 at 17:34:24

In Reply to: RE: 9" Jelco 750D tonearm alignment posted by Da He Hua on February 2, 2017 at 15:38:47:

Yes that is going to be a problem. The arc protractor only gives the correct solution if the pivot/spindle distance EXACTLY matches the parameters used to create the protractor (and that assumes that your printer output is correctly scaled for x and y axes which they almost never are). The errors rapidly stack up to give a result that can be quite far off the theoretical solution. Even if the original spec for the armboard was 211mm there is likely to be an error with this which makes the arc protractor less useful for accurate results unless you work backwards and fix the pivot spindle distance.
Use the "Stupid Protractor" instead if you don't want to redo the armboard or better still, use a Linear Offset Jig like the Feickert. Regardless of what method you choose, be very careful to have a snug fit for the protractor spindle hole over the spindle so there is no slop.

Secondly, do you play Pop LPs or mostly classical and jazz? If you play pop LPs, then a significant number of the original pressings from the 80s and 12" singles are cut quite a bit further in than the IEC min radius John quoted. They are cut to more closely match the DIN specification where the inner radius is 57.5mm and I even have some that are cut in to 54mm. In which case John's null points won't be quite the best solution for you. For jazz and classical, yes, the IEC radii he gave you will be the best. However, for pop material and 12"s you will start to get noticeable inner groove distortion given the hotter cuts of pop material.
The null points which best suit a "typical" pop 12" would be approximately 63 and 119mm.
Regards Anthony

"Beauty is Truth, Truth Beauty.." Keats

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Follow Ups Full Thread

Topic - 9" Jelco 750D tonearm alignment - Da He Hua 13:27:36 02/02/17 (29)

Glad you got sorted out.............. - viridian 14:57:00 02/04/17 (1)

RE: Glad you got sorted out.............. - Da He Hua 15:09:00 02/04/17 (0)

RE: 9" Jelco 750D tonearm alignment - Da He Hua 18:15:34 02/03/17 (0)

RE: 9" Jelco 750D tonearm alignment - hifitommy 20:46:24 02/02/17 (0)

RE: 9" Jelco 750D tonearm alignment - Da He Hua 15:51:20 02/02/17 (2)

RE: 9" Jelco 750D tonearm alignment - John Elison 17:21:00 02/02/17 (1)

Correct. Standard Linn mount - 211 mm pivot to spindle. - Opus 33 1/3 17:28:05 02/02/17 (0)

RE: 9" Jelco 750D tonearm alignment - Da He Hua 15:38:47 02/02/17 (2)

RE: 9" Jelco 750D tonearm alignment - flood2 17:34:24 02/02/17 (0)

RE: 9" Jelco 750D tonearm alignment - John Elison 17:18:31 02/02/17 (0)

RE: 9" Jelco 750D tonearm alignment - John Elison 15:32:40 02/02/17 (18)

RE: 9" Jelco 750D tonearm alignment - mr.bear 12:17:10 02/04/17 (0)

RE: 9" Jelco 750D tonearm alignment - Da He Hua 20:04:07 02/02/17 (3)

RE: 9" Jelco 750D tonearm alignment - volunteer 10:24:43 02/03/17 (1)

RE: 9" Jelco 750D tonearm alignment - John Elison 17:27:40 02/03/17 (0)

RE: 9" Jelco 750D tonearm alignment - John Elison 20:23:11 02/02/17 (0)

Thanks a lot, but still one question - Da He Hua 19:03:49 02/02/17 (12)

RE: Thanks a lot, but still one question - John Elison 19:18:53 02/02/17 (11)

RE: Thanks a lot, but still one question - Da He Hua 15:34:48 02/03/17 (10)

RE: Thanks a lot, but still one question - John Elison 17:57:15 02/03/17 (9)

RE: Thanks a lot, but still one question - Da He Hua 08:58:50 02/05/17 (1)

RE: Thanks a lot, but still one question - John Elison 09:26:13 02/05/17 (0)

RE: Thanks a lot, but still one question - Da He Hua 18:27:29 02/03/17 (1)

RE: Thanks a lot, but still one question - John Elison 18:36:17 02/03/17 (0)

Spec says 214 mm mounting distance and 229 mm effective length - Da He Hua 18:20:03 02/03/17 (4)

Unfortunately, most tonearm manufacturers don't understand pivotal tonearm geometry! - John Elison 19:05:07 02/03/17 (3)

Eureka moment?! - Da He Hua 07:21:04 02/04/17 (2)

RE: Eureka moment?! - flood2 13:07:20 02/06/17 (0)

RE: Eureka moment?! - John Elison 09:19:39 02/04/17 (0)

Follow Ups

RE: 9" Jelco 750D tonearm alignment - flood2 17:34:24 02/02/17 (0)

RE: 9" Jelco 750D tonearm alignment

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