Stylus Rake Angle
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 . |
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. |
Although my own experiments and experiences cause me to doubt some of the charts and statements on Yosh's webpage about VTA, overall it remains worth reading. http://www7a.biglobe.ne.jp/~yosh/vta.htm I will add that speaking as a cartridge designer, I find SRA and VTA to be different. For example, designing a cartridge with increased VTA will allow a shorter cantilever to be used, but doing so has the side-effect of stiffening the suspension vertically while leaving the horizontal compliance more or less unaffected. As a rough guide, at 0 degrees VTA, horizontal compliance and vertical compliance of the suspension wire will be the same. At 90 degrees VTA (which no cartridge does), the vertical compliance will be 0, while the horizontal compliance will remain the same as it was at 0 degrees. For all angles in between, you can figure out how the ratio of horizontal to vertical compliance changes in the suspension wire by calculating the cosine of the VTA angle. Note that I have deliberately not included compliance of the suspension dampers, therefore you should not jump to conclusions from the above. Some suspensions have linear characteristics, while other types have progressive characteristics, making it impossible to generalize. kind regards, jonathan |
Which type of lathe do you have? Its an old Scully (well, *all* Scully lathes are old...) equipped with a Westerex 3D cutterhead. The cutterhead does not need a lot of power and has a moderate impedance, we are easily able to drive it with our M-60 amplifiers. Kiddman, it helps to take a look at what is happening in the groove with a microscope. Of course every lathe has one, you can't do the work without it! We have a multi-color LED light source that we installed, so we get different colors depending on what we are seeing- the lands, the groove wall, or the bottom of the groove. As I said before, the defining quality of groove depth is the center of the groove. If you have high frequency modulation, that shows up under the 'scope like a groove with modulation on the walls. If you have bass information, the *entire* groove moves from side to side with the bass modulation. If the bass is out-of-phase, the groove will stay in one spot and seem to vary in width and depth. This sort of condition will knock the stylus right out of the groove and so has to be avoided. In natural 2-mic recordings it does not show up- only if the recording is multi-tracked to start with. I Googled for images of this stuff. Without a multi-color light source it can be a little hard to see, but there is a photo that appears at this link that is not bad for what I am talking about http://en.wikipedia.org/wiki/Gramophone_record Scroll down aways, the photo appears on the right hand side about half way down, just above the heading 'vinyl quality'. If you look closely at the grooves, you will see that they squiggle a bit. Those larger squiggles are bass notes. This is why I say the groove depth does not vary all that much, as the *entire* groove has to move to make the in-phase bass note. |
