RE: Forgive me if this is a dumb question, but...

Posted by John Elison (A) on July 5, 2012 at 20:13:49

In Reply to: Forgive me if this is a dumb question, but... posted by Mr Blue Sky on July 5, 2012 at 18:15:09:

Overhang is the shortest distance from the center of the platter to the stylus when the tonearm is moved inward across the platter spindle. It generally is not measured directly because most tonearms cannot be moved inward over the spindle. However, it is also the difference between the effective length of the tonearm and its mounting distance.

Effective length is the distance from the stylus to the pivot point of the tonearm. According to Rek-O-Kut, that distance should be 223-mm for your S-120 tonearm. Of course, it can vary slightly because different cartridges have different distances from stylus to cartridge mounting holes. There is no standardization among cartridges. Therefore, you say you measured your effective length to be 219-mm, which is quite possible if you are using a cartridge with a very short stylus-to-mounting-hole length. Most tonearms have mounting slots in their headshells to allow the cartridge to be moved forward or rearward in order to compensate for different stylus-to-mounting-hole lengths.

Rek-O-Kut states the following parameters for your S-120 tonearm:

Effective Length: 223-mm
Overhang: 13.5-mm
Mounting Distance: 209.5-mm

Rek-O-Kut does not state an offset angle, but my guess is that it cannot be more than about 21-degrees. These parameters do not provide a very good alignment. Many tonearm manufacturers do not understand alignment geometry and Rek-O-Kut seems to be one of them. Your choice for Baerwald's alignment is therefore an excellent choice. I believe it provides the lowest overall tracking error distortion between an inner groove radius of 60.325-mm and an outer groove radius of 146.05-mm. The alignment null-points will be 66.0-mm and 120.9-mm. Use these in the equations below to calculate mounting distance.

Baerwald's alignment, which we now refer to as Löfgren A, requires an offset angle of almost 25-degrees, so you will need to angle the cartridge inward in the headshell. There is usually enough slop in the mounting holes to allow for this. If not, you have to determine how to accomplish this or you cannot get a true Löfgren A alignment.

You also need to be very certain in your measurement of effective length. Check the distance from the stylus to the back surface of the headshell. According to Rek-O-Kut, this distance should be 50-mm for an effective length of 223-mm. Since you measured an effective length of 219-mm, this distance should be 46-mm on your headshell. If this is not the case, remeasure your effective length until you get a very accurate measurement. Only then can you calculate the correct mounting distance for Löfgren A.

Good luck,
John Elison

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Follow Ups Full Thread

Topic - Tonearm Mounting/Geometry Question.... - Mr Blue Sky 14:33:39 07/05/12 (18)

Yes, maybe... - tketcham 17:52:32 07/05/12 (10)

Forgive me if this is a dumb question, but... - Mr Blue Sky 18:15:09 07/05/12 (9)

RE: Forgive me if this is a dumb question, but... - dtut 10:02:01 07/06/12 (4)

Not sure I understand.... - Mr Blue Sky 12:06:32 07/06/12 (2)

RE: Not sure I understand.... - dtut 15:18:09 07/06/12 (1)

Desperation is the mother of invention... - tketcham 05:59:53 07/07/12 (0)

That is a... - tketcham 10:23:22 07/06/12 (0)

No dumb questions, only dumb designs... - tketcham 04:32:18 07/06/12 (2)

RE: No dumb questions, only dumb designs... - John Elison 07:15:27 07/06/12 (1)

Worst may be best... - tketcham 08:23:30 07/06/12 (0)

RE: Forgive me if this is a dumb question, but... - John Elison 20:13:49 07/05/12 (0)

RE: Tonearm Mounting - M3 lover 16:21:45 07/05/12 (0)

Sounds right to me... - John Elison 15:56:06 07/05/12 (5)

If I had known math ... - reelsmith. 17:27:56 07/05/12 (4)

CD players rule! ;-) /nt\ - John Elison 20:32:56 07/05/12 (3)

Oh, John.... - JimK 08:07:22 07/06/12 (2)

RE: Oh, John.... - John Elison 09:50:29 07/06/12 (1)

I miss my tubes. - JimK 12:56:56 07/06/12 (0)

Follow Ups

RE: Forgive me if this is a dumb question, but... - John Elison 20:13:49 07/05/12 (0)

RE: Forgive me if this is a dumb question, but...

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