Stylus Rake Angle

There is some confusion here due to terminology, I believe, as well as a lack of clarity, in some cases, of what is really happening.

An attempt to clarify:

1. The cutter head height is constant across the lacquer, an therefore, the final pressed record.

2. The "no signal" actual groove depth is a constant due to #1, if we ignore slight differences in thickness of the lacquer, slight vertical error of the lathe platter, and other such imperfections.

3. Groove depth at any point, when stereo signal is present, will vary if there is any difference between the left and right channel recorded information. This MUST be the case, as this is how stereo records work: the vertical modulation of the groove (which indeed represents changing depth) represents left minus right channel information.

4. If we define "groove depth" as the actual measurement of the the distance from the bottom of the groove to the top of the record at any point on the record, #3 above is true. IT DOES CHANGE.

Now, if we define "groove depth" as a no-signal SETTING based on the height of the cutter head when cutting a particular record, that does not change during the cutting of any one particular lacquer after the cutting process begins.

To sum up: as I read this thread I perceive that some are talking about a SETTING with no signal going to the had when referring to groove depth, while others are talking about the ACTUAL measured groove depth at a given point on the record. They are two difference concepts.

The actual measured depth, if one physically cut a record and looked at the grooves on end with a powerful microscope, would indeed be a changing measurement on a given stereo record when there is indeed a difference in left and right channel information. This change will be small, as bass information is not recorded in stereo, but vertical modulation (and modulation means a changing parameter!) is indeed there.

Confusion like this often exists when one party with experience in a given field sticks to the terminology used in that field, instead of trying to put himself in the place of someone who is not in that field and not experienced wiht the typical jargon of the field. In technical teaching situations I have always found that it is best for the experience person to not get hung up on the "insider terminology", but rather to put himself in the position of the inexperienced person to try to understand exactly what that person is trying to ask.

Trying to help clarify, not criticize.

A question was posed about why the angle of the cutter and angle of the stylus need to be the same.

The trigonometry dictates that for small angles of deviation it does not matter much as the cosine is changing extremely little for angles of 1,2,3 degrees. For instance, cos 3 degrees = .9986!

Visualize this: a pointed shovel whose shape is a "V", with the "V" portion 10 inches tall. Put the shovel straight into the sand to a depth of 5 inches, and then pull it along making a "V-shaped" groove in the sand.

Now, with the shovel in the groove, lean it 3 degrees forward or back. The "V" shape of the shovel fits the V groove almost perfectly at the 3 degree angle, even though the groove was cut with the shovel vertical, or at 0 degree lean angle. It has to: the cosine of 3 degrees is .999!

But, if you lean the shovel to 15 degrees you will see that only the upper part of the groove will contact the sides of the groove, the rest of the shovel will be pulled up away from the groove. We'll only have 2 short contact points.

The shovel represents the stylus, of course, the sand the record, and the V-groove the cut groove in the record.

So, in reality, small deviations of stylus angle compared to cutter angle mean very little. Large deviations represent a increasing compromise as the difference in angles gets larger.

There is such a thing as "good enough" indeed!

As for no VTF change with VTA change, it is complicated. Springs do NOT do acheive this as they are linear force per displacement devices, and VTF varies as a trigonometric function. Therefore, the compensation system for changing VTF with VTA to make VTF constant would need act in proportion to a trig function. Too complicated, best to adjust center of gravity height for minimum change in VTF with a given VTA change, and if you make a big enough change in VTA to actually change VTF meaningfully then just adjust VTF.

All tonearm guys who say their perfect height of the pivot point, the height of the counterweight, the underslung nature of their counterweight, or their spring, are not very good at trig, calculus, and running the experiments or they would know that they are wrong and then confirm it with the tests.

Changing VTA at the headshell brings with it several other problems while trying to solve a problem that readjusting the counterweight would have solved anyway.