Table of Arm Data

Linear Trackers & Arms equipped on system players are omitted from list.

NOTES: There are many discrepancies in the descriptions/performance of arms due to the following reasons.
1) Manual and model do not always coincide (manual is not enough if there are too many modification:
history of models may be required). Some dimensions (esp. effective length) of same model may differ between early manual and later manual even though the product itself remains unchanged. And vice versa: same model may change dimensions without referring to them. Often we find irregular conversion from inch to mm in the manuals for UK/US products.
2) Incorrect worked angle: the processed tube will tend to change the angle after a while
(someone said that Mr Breuer was watching his arms for more than 3 months).
What is the worked allowance for the offset angle of bent arm?
3) Misprint or dubious description in original documents or repetition from secondary sources. Moreover many documents show unreliable descriptions on error angles irrelevant to the geometry of arm. There is no standard style of description/definition about error angles. Some adopted average error angle divided by groove radius (for example: 0.1degree/cm). Other adopted maximum error angle at optional radius of groove or size of record. Usually maximum error range +/-degrees are mentioned without specifying the range of groove radii. Who knows: the designer is nonchalant about geometry or the manual is wrong from typo or the manufactured arm is not made in accordance with drawing/manual etc?
4) Strained to some fixed ideas such as Baerwald/Loefgren designs. For the honour of them, please note that so-called Stevenson/Baerwald/Loefgren designs are not directly related with them who gave mathematical solution, method and thought on lateral tracking angle error.
Some fixed ideas of designs will lead us to overlook the actual product as it is produced.
In case of my KMAL M9BA MK3 Serial No. 75187(fixed shell with 2 thread holes for inch screws),
the linear offset measured is 77mm(19.7degree)
- far from 89mm(23degree) as proposed by Audio Magazine 1980 which stated O16.2 A23 NP60/118.
*Keith Monks M9BA MKIII L228.6 O12.7 A19.7 NP60/94 when linear offset is 77mm.
I suppose that the actual geometry of my arm is similar to the above simulation.
Arm Distance (Spindle Centre to Base Centre) Mounting template indicates 8.5inch
Arm Effective Length (from arm pivot to stylus): nominal 9inch
Overhang: 0.5inch as a result and also matching to my arm. There were various headshells so that the offset angles might be differing among these shells (perforated one/black thin plate shell of mine/big and robust one as seen in the picture gallery of The Vinyl Engine). Anyway incredible offset angle 23degrees and overhang 12.7mm were described in documents for early M9BA with robust shell (M9BA MK I) originally produced by Audio & Design around 1967. But alignment under such geometry shall indicate funny null points such as 41/137mm - it might be intended for transcription disks: effective 9inch arm for 12inch records, 12inch arm for 16inch records? See also null points on Decca International/Professional.
In case of my Infinity Black Widow with silicon oil bath and SME type bedplate 60.5x41mm.
Audio Magazine 1980 stated L237 Distance222.641 O14.359 A21.017 NP60/110.
*But original setting template indicated distance 222mm and I think that L237/Offset 21degrees/Overhang 15mm/Distance 222mm shall be more realistic design figures. Then Null points 67/103mm though I could not confirm these figures since I have not original alignment template. Anyway the linear offset length is approx. 85mm as I measure.
5) In case of Thorens, there is much confusion due to the different exchangeable head tube (Endrohr) types such as TP62 & TP63. Actual offset, Overhang & Effective length shall be determined with the combination of head tube/shell and arm tube.
6) Some old & longer arms are designed for transcription or sound track record (16inches). I think there was standard broadcasting equipment recommended by NAB in USA or BTS in Japan though I could not find any specific document but  suggestion in old catalogues. It is interesting to note that the distance (from arm pivot to turntable spindle) of such arms (Audio-Technica AT-1501II, Denon DA-302, Grace G565 & Gray 108 etc) is mostly around 270mm. Decca International/Professional arm has strange geometry in order to play back SP, EP and LP as well. This is the meaning of "Professional" or "Broadcasting" use.

I believe the users know the worked products better than designers or manufacturers. Hence please email to me if you find reliable data confirmed/measured by yourself (hearsay evidence is unwelcome - I've had quite enough of such kind).

Above and following calculations are based on my EXCEL sheets about Overhang adjustment on shell & comparison of arm designs which can be used at your end after saving it if you like.

Importance of Linear Offset length rather than offset angle in arm alignment design. Effective length x SIN(offset angle)=Linear offset length. Offset angle is ASIN(Linear offset length/Effective length). (Total of null points if any)/2 equals Linear offset length. Often users discuss offset angle without questioning why some alignment tools can be applied on many different arms with certain linear offset length.  Arms with same linear offset length have potential for same alignment irrespective of arm length  - this is the basis of each alignment tool for two null points. Of course linear offset length can be different as per arm alignment design.

Null points b, c = Linear offset length +/- alpha.  Proper alignment is obtained by adjustment of alpha: see Alignment Gauges.

Please note that "geometrical offset angle" is not same as headshell offset. Headshell offset or German wording for offset "Kroephung"( "bending the pipe") is leading us often to misunderstand the geometrical meaning of "offset angle". See above drawing. HO=Headshell offset angle to the straight pipe measured at the neck of shell or at the centre of slots for mounting cartridge. A=true offset angle is measured at stylus point against the imaginary straight line from stylus tip to arm pivot. Hence it is not easy to measure the offset angle from appearance. Linear offset can be measured with a carpenter's square. The overhang adjustment on shell is not changing linear offset length as far as the cartridge is mounted square within shell (see above right drawing) - that is changing the effective length and the distance between two null points - see the details on another sheet: Alignment.xls   
IMO: The discernible limit on our adjustment of cartridge azimuth on shell is: 0.5mm in length and/or 1 degree only so that I cannot believe too much in any method of alignment. The thickness of grids on protractor must be made very thin and we must discern the difference of 0.1mm order for obtaining exact angle alignment as seen in the following table. Man confident of having such good sight ability might be happy enough. Now I have poor sight. [15inch monitor screen (4:3=12x9inch) having 1024x768pixcels : one pixel size is about 0.3mm - Can you find any dead pixel/dot on your screen?] It resembles "the problem of mice who bell the cat" in Aesop's Fables. There is much difference between armchair theory or calculation and actual practice. According to another chart indicated in my recspecs page, the adjusting method of anti-skating bias by seeing the deflection of cantilever is also not valid. But in real world, self-assurance or conceit prevails among some audiophiles who would say "we did it perfectly", but nobody can testify their performance.

SME drawings for series V/IV (& 300) are also misleading or confused by indicating: 

1. headshell offset D instead of true offset angle (=D minus included angle between grey line and wand centre line) 

2. pivot to tip distance (A) projected laterally to horizontal line instead of straight effective line from pivot to tip

The above confusion seems to be arising from shell design. The following drawing of AT-1120 for example shows various cartridges with 10±3mm distance from the centre of mounting holes to tip can be used/aligned on this shell. This allowance 10±3mm (no mention of tracking force) should comply with JIS standard(1979) about pick-ups. IEC(1987) recommended cartridge mounting holes centre to tip:  9.5mm +/-1mm at the tracking force recommended by the manufacturer though the latter recommendation is not adopted by many cartridge makers except Audio Technica/Shure etc.

Here headshell offset angle equals actual offset angle because of the following reasons:

Thus there is no fixed alignment in design, make and performance (so that I believe alignment with protractor is effective as compromising method). Please also look into various alignment tools.

BTW:Most of straight arms including SME/Denon DP-7F etc are not straight actually because stylus-arm pivot-countershaft line is not exactly straight. When seeing from stylus point to arm pivot, the countershaft is biased a bit in order to counterbalance laterally the rear part of cartridge whose centre of gravity is set aside to centre line of straight arm. Thus such straight looking arms might be called just slim type of S-shaped arms. Do you like slim one (so-called straight pipe) or fatty one (S-shaped pipe)? AT-1100 sold in Japan around 1979 had interchangeable pipe system: Integral spare pipe ASP-1(straight pipe with fixed shell), Universal spare pipe ASP-11(detachable shell and S-shaped pipe as usual Japanese users prefer) and sub-counter-weight W-3 for using ASP-11. Meanwhile AT-1120 cannot change its straight arm pipe. Both AT-1100 & AT-1120 do not have lateral balance weight, whereas their stylus-arm pivot-countershaft line is exactly straight!

In 1989 Mr. Ho in Taiwan proposed "perfect dynamic balanced arm" and lateral balancing device for shell+cartridge by GB 2229848 (possible improvement for AT-1100/1120).

Though above design looks better and simple for lateral balancing, but its head weight is increased. So I admit that slim type of S-shaped arms is preferable as practical compromise.