Stylus Rake Angle

I've found a1981 article in my "files" which explains things better than I've been able to, and uploaded it on to my blog:
Vertical Tracking Angle Explored - Keith Howard, Hifi Answers 1981

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Sorry - the article is from Practical HIFI not HIFI Answers - (from the days when there were too many hifi mags to keep track of...)

Csontos: I perhaps shouldn't have mentioned cantilevers per se, as opposed to the function of the cantilever. But have a read of the article mentioned.

John

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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.

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Raul

The analog medium is full of imperfections and we have to deal with in the best way we can. Sometimes I think is an endless enterprise.

At the end each one of us have its own targets and MUSIC sound reproduction and each one trade offs choosed are related to achieve those targets.

Yes, I agree all is compromise with regard to set up, especially with regard to SRA and VTA which are decided by the cartridge manufacturer. It is up to each listener to decide what is acceptable to them, and to be aware of why it is so.

Csontos

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.

The issue isn't that there is or isn't a standard (if recommending anything between 15 and 25 degrees for VTA constitutes a useful standard), but that it appears that the SRA parameter is variable depending on the mechanics of record cutting, and is at best an approximation of between 91 and 95 degrees, and can vary across a record. It also varies with downforce, and with offset, which in turn depends on chosen geometry and the accuracy with which it is set.

Until someone makes a headshell which allows variation of VTA/SRA without altering overhang and downforce, then those will be factors...

More info - old articles- here

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Atmasphere:

Take it as a definition unique to the technology that 'groove depth' means how deep the groove is with no signal.

I understand that. It is the reference point. A silent groove has a fixed depth and smooth sides.

If the cutterhead were to rise and fall with respect to the lacquer surface, then we would see a varying groove depth

Clearly that is the case.

But when the cutting stylus records any signal other than a pure mono one it must move more and less deep into the lacquer, otherwise how can the signal be cut? That was what I was getting at and confused by your answer. I didn't mean the whole mechanism moved, solely the cutter itself.

It's an interesting subject. Maybe I should get my hands on a cutting lathe...

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Atmasphere,
Surely the groove depth changes with signal? A right channel signal for example must cut into and out of the lacquer at 45 degrees. I can see that a heated cutting stylus will help the process, but then does that affect the final profile as the material cools?

Lewm,
The VTA is the angle from the cantilever pivot to the stylus tip relative to the record, which ideally should be the same angle as the equivalent angle a line from cutter pivot to the cutter stylus makes with the lacquer if there was no "give" in the material. Both can vary. Apparently there could be 10 degrees of a difference depending on the lathe.

But the cartridge is designed such that for an optimum downforce the generator is centred, and the resulting cantilever angle is the VTA. So the angle of the stylus relative to the cantilever is fixed and the two must vary together.

Now while the stylus might be set at 92 degrees, the cantilever may not be at the same angle as the the cutter. In which case there will be a distortion in the playback, similar to horizontal tracking error. Any adjustment to set VTA - the cantilever - to a particular angle will change the stylus rake as well, perhaps away from the average 92 degrees.

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Csontos, you said:

You are mistaken. VTA has nothing to do with the angle of the cantilever. The angle of the stylus relative to the cantilever can vary wildly from one cart to another and therefore result in huge differences in cantilever/surface angles. VTA is set by the cutting stylus itself. Therefore there doesn't need to be a reference to VTA adjustment at all. It's done with as soon as the laquer is cut. The pertinent function to play back is SRA, the thing that follows. The fact that the cantilever angle changes with SRA adjustment is incidental.

You need to do your homework and think more on this.

Vertical Tracking Angle is a cartridge property. The clue is in the word "tracking".
The fact that it may not be the same as the equivalent angle used when the record was cut, as you mention but fail to realise its relevance, is what can lead to distortion in playback.

Atmasphere, you said:

Yes, the groove wall is cut at a 45 degree angle, so if you were to cut an out-of-phase bass signal, the groove would indeed modulate up and down. Of course, the needle would not be able to track it, and such a signal fortunately does not exist in nature. If we encounter studio productions where out-of-phase information is a problem, we have a simple passive processor that takes care of it. So groove depth can be considered a constant.

I wasn't talking about out of phase signals, but left or right signals. I can see that a mono signal varying only in amplitude, side to side, will maintain a constant groove depth which doesn't vary, but stereo?

I'm not trying to make a point but just trying to understand the process and its implications for playback, as coming from a mechanical engineering perspective, I am familiar with lathes and cutting tools, and the issues involved in machining different materials. That's why I'm interested in knowing more.

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Peterayer and Stringreen,
Sorry to veer off on to record cutting.

To get back to the OP. The reason why there is an issue with regard to SRA and VTA is that they affect different things. An appreciation of what each term actually means helps to understand the issues. An appreciation of why cartridges have the geometry they do also helps. Reading the articles I linked to will be useful in doing this. Some might find them too technical, in which case, ignore the subject and set your arm up to sound as good as you can.

Csontas:
from your reply, it is clear that, if you have read the articles and are none the wiser, you fall into the last category above. Please don't insult me or question my motives.

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Csontos,

If the cartridge manufacturers want to refer to SRA as VTA and vice-versa, so what?

They can call it what they wish, as can you, but the terms are distinct, and in adjusting every cartridge varying one varies the other.
VTA in a cartridge should be the same as the equivalent angle in a cutting lathe.
SRA should be the same as the cutting stylus angle.
My point is simply that optimising one does not automatically mean that the other is also optimised. This was the argument for using SRA rather than VTA to set up in the first place.

I used the cantilever angle as a easily understood approximation of VTA. The actual angle is that between a line drawn from the cantilever pivot point to the stylus tip and the record surface. For most cartridges this is close.

Lewm

Once the LP is cut, why should the cantilever give a damn about the cutter angle? The stylus "cares" about that in terms of SRA. So I would think that you set VTA so as to obtain proper or optimal SRA

The reason there is such a thing as VTA is that the stylus moves through an arc which is described by a radius the length of which is approximated by the cantilever and ostensibly at 20 degrees +/- 5, to the record surface. The reason for that is that the record was cut in a similar manner, the cutting stylus (while set at, say, 92 degrees to the lacquer surface), also describing an arc, as it is constrained within the cutting head. Variations in VTA cause distortions. They may be less of an issue than SRA but do exist.

Csontas: If we must continue:

John, have you read this article in it's entirety yourself? It corroborates every single point I've made without fail! I'm now wondering what your motive is in participating in this discussion.

Yes I have. I read it when it was published. I understand the difference between SRA and VTA. My motive in contributing to this thread was to try and help those who obviously thought SRA and VTA were the same thing, see that they were different and had different effects. I have provided links which is more than you have. Make of them what you will.

John goron. I don't see why you should feel insulted. But I certainly have been. To suggest that those participating in this thread don't understand the terms borders on an insult to them as well. We all understand the terminology and what's clear is that you've been just playing semantics.

If everyone understood the terminology there would be no thread.

You reckon the difference between VTA and SRA is a semantic one and so adjust the height of your arm on the fly and find it sounds better. Good for you. However, some might wish to know why it is the case in order to improve their understanding.

From what you have posted anyone who knows the subject (some of the previous posters) will see that you are confused about why that is so. You are not alone Don't feel insulted.

I don't know why you are so concerned with what I have posted and why. I simply post when I feel I can contribute to what appears to be a misunderstanding or a confusion regarding vinyl replay.

I don't care what your motives are, and I will leave it there.

Atmasphere:
Thanks for that. I was obviously on a different track regarding the terminology of record cutting lathes- the meaning of groove depth, cutterhead, centre, etc.

It is a good example of why familiarity with specific terms in unfamiliar areas is beneficial. Which type of lathe do you have?

John

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