Stylus Rake Angle

On the subject of stylus overhang:
If the pivot to spindle distance is set exactly right, meaning +/-0.3mm of the recommended, because that is the best anyone can do, then it seems to me that small errors in overhang (say +/-1.0mm, but I would have to do the geometry before settling on that margin) can be tolerated.
Reason: None of the accepted tonearm geometries achieve more than two points on the arc of the stylus tip where there is tangency. The various algorithms differ only in the locations of these two points along the LP surface (and they also do differ in the amounts of tracking error at other points along the way, but I am not debating that here). A small error in overhang, assuming P2S is correct, will only move those two points of tangency by small distances in or out on the radius of the LP. So long as those two points remain on the playing surface, what is lost?

You answered your own question.

With regard to the distinction between SRA and VTA, there is also an equivalent distortion to Horizontal Tracking Error if the VTA is not that at which the record was cut. This Vertical Tracking Error is distinct from SRA and will influence tracking performance.

So with any given cartridge optimising SRA may mean VTA being compromised...

Atmasphere, you said:

As the stylus wears, sometimes you have to make little adjustments, like the stylus temperature. Funny thing- it cuts a slightly different angle depending on the temperature. Some LPs don't have very much in the way of dynamics so you can change groove depth a bit to allow for more time on the LP, conversely if something has a lot of dynamics or out of phase bass, you might cut a little deeper. So groove depth affects stylus angle too.

From what I understand, the cutter head angle may be a particular value, but the resulting profile on the record is different due to the springiness of the lacquer material which varies with temperature, such that the resulting optimum SRA is not that at which the record was cut. Variations in modulation mean that the cutter has to dig more or less deep, thus varying temperature and hence the profile, so that an optimum SRA at one point on the side may not be so at another. Would that be correct?

Lewm, you said:

A small error in overhang, assuming P2S is correct, will only move those two points of tangency by small distances in or out on the radius of the LP. So long as those two points remain on the playing surface, what is lost?

As you say, the important thing is the position of the two null points. Not because of their tangency, but because they define the distortion. As they become further apart, there is increasing distortion across the middle of the side. Closer together, the extremes are tracked with more distortion, particularly towards the centre. Small changes in null position make little difference.

However, that presupposes that the offset angle is set correctly which, rather than overhang or P2S, is , in my experience, the most difficult aspect of set up.

.

Optimal SRA is an average based on the average 20 degree cutting angle standard, give or take. Temperature becomes moot as soon as changes in depth are introduced by modulation since that is accompanied by groove angle changes anyway. However as Atmasphere pointed out, average depth changes at the hands of the engineer and imperfect tooling set-up will certainly require a change in SRA. VTA refers to cutting angle. For all intents and purposes, VTA and SRA are virtually the same thing because it is impossible to perfectly maintain standardized specs. This is why the only way to match the two is by 'listening' and at best, listening on the fly.

Dear Lewm/Peter/all: Nothing changed on my mind about, overhang always is important. Things are that for many people overhang changes " makes " almost no diference on the quality performance and not because it does not makes a difference but because they are unaware of how the system sounds when overhang is off. It's not easy to be aware if you don't know what to look for: if you are not trained to do it.
In the other side in the very first time/moment that the cartridge stylus hit the LP grooves the overhang/VTA/SRA/VTF suffer minute changes due to the imperfect medium and maybe because of this I could said it has not " anal importance ".

This is something similar as the RIAA eq. deviation where I supported and support the critical importance on accuracy.
I say that a prety decent RIAA eq. frequency deviation of +,- 0.1 db is not enough and that a RIAA frequency deviation of: +,- 0.015 db is better and we can hear the difference IF we are trained to know what to look for during playback.

Now, all cartridge/tonearm alignment parameters are important and critical to achieve a top quality performance and we have to take care on each one if we want that the cartridge can shows us at its top performance.

In a pivoted tonearm the cartridge alignment start when we choose the the type of alignment: Baerwald, Löfgren B , Stevenson and the like.

Löfgren defined the geometry equations for a precise cartridge set up where we have mainly to know the overhang and offset angle ( between other parameters. ).

This is a sin-equanon the very first step for the cartridge can shows it at its best.
So IMHO overhang and offset angle ( for a choosed alignment geometry equations. ) must stay with out changes when other cartridge set up changes.

The different alignment equations is a trade offs " game " depending on what we want/prefer on distortions level between null points and outside null points at outer and inner LP grooves.

The alignment equations we choose optimize those distortions inside that choosed alignment in a way that any tyni deviation on the overhang and/or in offset angle cartridge set up produce a different kind of distortions to the ones choosed with different trade offs.

That we can hear or not the new distortions/trade offs does not invalidate the importance that on each alignment the name of the game is: accuracy that must stay that way always.

The target/main subject of any cartridge/tonearm geometry alignment is to do it as accurate as we can because we want optimized/lower distortions.
Tyni deviations from that " accuracy " increment in exponential way those distortions so we don't want to have this.

We all are very sensible to VTA/SRA changes and changes on Azymuth because we are aware of the differences on sound with these changes on cartridge set up and because we are accustom to do it and to hear the changes in performance when the overhang changes we are really unaware on how we detect it or how we listen it.

We have to learn trhough a training to be aware of it.

As I said, it's tiresoem/nightmare to change overhang each time we need it ( for VTA/SRA/VTF ) but we need to do it especially when we are doing cartridge comparisons or when we are fine tunning a cartridge.

Maybe some of you could remember that several times I insisted to have a proved and repetable evaluation/set up process that can permit to be aware of different kind of distortions and quality performance levels and know teh why's.

A easy way to be aware of overhang misalignment is to choose a well know LP tracks with bass range content and listen the system transiente response at different overhang values. You will be surprised on what you can hear down there those overhang changes.

Regards and enjoy the music,
R.