Eminent Technology ET-2 Tonearm Owners

09-16-13: Ct0517
Random Included Record Angles When they Make Records
...record masters are cut with random included angles by the cutter. The angle of the cut when the record master is made.
Recording Groove Contour
a. Included angle 90 degrees + 5
b. Bottom radius 0.00025" max.
c. Width--Monophonic .0022"--.0032"
d. Width--Stereophonic, Instantaneous .001" min.
Minimum Inside Diameter of Recording 4 1/4"
Runout of Recording Grooves Relative to Center Hole .050" max.
Notice the record included cut angle standard that was set can be 90 degrees give or take 5 degrees....:^(
So there is no standard.

The angle that the cutterhead is placed at when a record is cut results in an included angle in the final disc. This included angle must be duplicated with the reproducing stylus or distortion will result.

The problem today lies in standardization of the angle by record manufacturers and corresponding standardization by cartridge manufacturers. Presently most records are cut with resulting vertical angles between 16 and 20 degrees. The average vertical angles of cartridges manufactured today is slightly higher than 22 degrees. The result of this mismatch is less than optimum performance for many cartridges."

How important is the VTA adjustment to you ?

1. The "included angle" has nothing to do with VTA. The included angle of 90 degrees is the angle between the 2 45 degree walls of the groove. ( 45+45=90 ). In theory if the cutterhead is set up with an error of say 5 degree in the "included angle" then you would possibly need to adjust azimuth.

2. One of the fundamental problems is that the cutter moves in a fixed plane, whereas the stylus moves in an arc about the cantilever pivot, and therefore all cartridges with a conventional cantilever produce distortion. The notable exceptions are the Decca London Cartridges and the original Ikeda cartridges both of which do not have cantilevers and therefore these are the only cartridges that do not have this distortion built in. I own the Ikeda and have personally set up around 20 Decca's over the years. The speed, lower distortion and lack of phase and time smear with these cartridges is superior to anything else for the reasons outlined in the 1st sentence of this paragraph.

3. Cutterhead angles are a minefield as they varied historically over the years and different cutting lathes were set up with different cutting angles. There was a standardisation of sorts in the 60's but bear in mind the US settled on 15 degrees +-5 degrees and the Europeans settled on 20 degrees +-5 degrees.
The actual cutting angle used would also depend on how the engineer sets the equipment up and that is unpredictable. Springback is a common problem when cutting and this will alter depending on the composition and quality of the lacquers used ( they are soft ). Temperature is a big factor and if the lacquers have been stored at room temperature, as opposed to the recommended cool room temperatures, then often engineers would alter the cutting angle to get a clean cut due to the changing properties of the lacquers at different temperatures.

A few points to note :

Increasing the room temperature by 5 degrees F or approx 3 degrees C will lower the tracking angle by approx 1 degree.
Increasing the tracking weight by 0.1g will result in a lowering of the tracking angle by approx 1.5 degree
A spherical stylus profile will help to reduce these distortions in points 2 & 3 above.
If you add lead mass to the ET2 and remove the decoupled counterweight, as suggested earlier in this thread, then VTA doesn't matter as the increased distortion from a tracking angle error of +-5 degrees is almost certainly significantly less than the distortions introduced by the addition of lead mass and removal of the decoupled counterweight.

For ET2 aficionados, with a conventional cartridge that uses a cantilever, the combination of tangential tracking and a spherical stylus would minimise distortions due to VTA issues. I have run the Denon 103 which although not the ultimate in transparency, produced very good timing and coherence. The EMT TSD15 with spherical tip option would be an interesting cartridge to try.

Frogman - I think the arm simply sounds better with moderate and similar torque at all the screws. I adjust the VTA adjustment screws so that the adjustment can still be made without loosening the screws; but with some effort

Based on the years with mine I think this is really good advice Frogman.

Frogman - VTA adjustment on the fly is, for me, THE most important feature of the ET2. I find it invaluable and use it all the time.

I agree plus the fact it tracks in a straightline.

In the early days I was trying to figure the arm out and did not even notice how Bruce designed the VTA system in the ET2.
I was ignorant to it. How many ET2 owners are not aware (or take it for granted, not notice) that the VTA system is on a gearing system? The ET2 VTA cylinder mechanism (for lack of a better word) pulls the armtube in as you raise VTA and back out when you lower VTA. So it maintains the VTF and alignment.

I just tried this again with my Dynavector tonearm the other day. Lowering VTA increases VTF. Raising VTA lowers VTF. Some are really anal about how they set VTF on their tonearms. Just be aware you are affecting your VTF.

Dover

The "included angle" has nothing to do with VTA

Cutterhead angles are a minefield as they varied historically over the years and different cutting lathes were set up with different cutting angles. There was a standardisation of sorts in the 60's but bear in mind the US settled on 15 degrees +-5 degrees and the Europeans settled on 20 degrees +-5 degrees.
The actual cutting angle used would also depend on how the engineer sets the equipment up and that is unpredictable. Springback is a common problem when cutting and this will alter depending on the composition and quality of the lacquers used ( they are soft ).

Temperature is a big factor and if the lacquers have been stored at room temperature, as opposed to the recommended cool room temperatures, then often engineers would alter the cutting angle to get a clean cut due to the changing properties of the lacquers at different temperatures.

first statement is true on its own.

but in the data that you provided especially the last sentence - "engineers would alter the cutting angle to get a clean cut due to the changing properties of the lacquers at different temperatures"

With the ET2 VTA system angle changes can be corrected without affecting VTF and alignment - see previous post. this is also documented in the manual. This is what I was referring to.

Dover when you say

Increasing the room temperature by 5 degrees F or approx 3 degrees C will lower the tracking angle by approx 1 degree.

Lets say we have a situation where the room is left alone to go up in temperature. So the sound will become more warm and full bodied - less treble brightness - as you have lowered the tracking angle ?

Is this because of warmer plastic (record) ?

Can this explain why the music can sweeter (warmer) toward the end of a session?

Ct0517..
Increasing the room temperature by 5 degrees F ( 3 C ) is enough to soften the rubber suspension in the cartridge and drop the VTA by 1 degree.
I would assume by the time you have finished a session you will have softened up the suspension and this may explain some of what you hear.
Where you live it is quite easy to experiment - start with a cold room and warm it up, or put a lamp over the cartridge so the heat is localised. You will hear quite a difference - as the cartridge reaches optimum temperature the sound opens up and becomes more natural, as you overheat the cartridge the sound will literally go gluggy. What I have experienced is some cartridges mistrack on a seasonal basis (winter vs summer) here in NZ even though the temperature swings are not large, eg the Shelters. The Benz's generally spec out the optimum temperature and humidity ranges in their cartridge packaging.

Dover - in the winter the OTL's are enough to keep my room at the temp it started at - heating vents closed. The last couple summer months with the door/windows closed in my basement room the temp will go up 1 degree every hour. The OTL's are like two 50 inch plasma tv's as far as heat out put goes. With the door or window open this drops by half - 1 degree every two hours.