stylus for mono vs stereo grooves

[Bran Kulez]

ld wrote: BK, if you extend the two groove walls they intersect at a point. The horizontal plane containing that point should be the datum for dimensions A and B.

Got it, thanks!

[Bran Kulez]

So here is the revised drawing with the dimensions ld provided, they workout perfectly.

The next step would be to draw a 1.0 mil stylus and insert it into the groove as Ld suggested. The exact location of the 1.0 mil diameter dimension on the actual stylus tip, the angle of the cone and the radius at the tip of the cone seem to be the crucial dimensions. Any input would be appreciated...

[Ldg]

The next step would be to draw a 1.0 mil stylus and insert it into the groove as Ld suggested. The exact location of the 1.0 mil diameter dimension on the actual stylus tip, the angle of the cone and the radius at the tip of the cone seem to be the crucial dimensions. Any input would be appreciated...

All good stuff, BK here's some input to help draw the stylus.

The stylus ball end is a half sphere, and you know the radius is 1.0mil. It will contact the groove walls where the tangent on the circular section is exactly 45 degrees, the groove wall being at 45 degrees. This is the big clue !

Above the half sphere, the included angle of the cone is between 40 and 55 degrees.

Prepare to be amazed, BK, and remember those groove dimensions are abs min, not typical !

[Bran Kulez]

Got it, Thanks!

I'll sketch it out after I install an air-conditioner for the little lady...

[Bran Kulez]

Wife is cool and happy...

So here is a sketch of a stereo groove per ld's dimensions...



and a side by side comparison of where a 1.0 mil stylus tip intersects the groove walls on mono and stereo grooves...



I realize that this is hardly conclusive and doesn't prove that a 1.0 mil stylus tip will damage a stereo groove, but it does appear that doing so would be less than ideal... any thoughts?

[Ldg]

Good stuff, BK. That looks about right to me. But one needs to remember these are absolute min spec width/depth grooves, not typical. And the abs min stereo dimensions don't describe the situation with mono programme material. With mono grooves, depth/top width is constant. With stereo grooves, depth/top width varies according to programme material.

Back to the OP, for mono programme material cut on a stereo lathe, depth would be at the nominal centre of the range. This will be much larger than the abs min stereo spec, because the is no vertical modulation in mono. What this is in practice, I don't know. But since the playing time of mono and stereo LPs is about the same, my guess is the nominal centre range groove dimensions for mono and stereo is about the same as the mono case.

If you go on to draw a stereo spherical (0.7mil radius) in a stereo groove you'll see how high it can ride, during stereo programme material worse case. Also how there's not exactly much space for line contact stylii to avoid riding the crown worst case if the claimed contact lengths were true...........

But yes, a 1mil spherical stylus rides the crown of a stereo groove with stereo programme material worse case spec, and that probably isn't good, hence the recommendation not to do it. It's a close call though, and much depends on what typical-min is in practice. I don't know enough about real stereo groove depths to comment, but Yosh's excellent site might well have some more info.

Good stuff, BK.

[Bran Kulez]

Thank you ld, you have been extremely helpful.

btw, Yosh's site is amazing!