STP distance. Is it critical ?

Dear Nandric,

I agree with Jonathan (who am I to disagree with such an expert!?).

The way I read the SAEC engineer statement emphasizes what is being discussed in the thread. Changing one of the three "dimensions" changes the other two for a given geometry. If the STP increases, so does the effective length, the cartridge offset angle shallows. Each geometry has a different ratio, but the same principles apply.

If one of the dimensions change without changing the other two, then the geometry is different.

Take a glance at this table to see how the dimensions are interrelated. This table is for a single geometry / location of null points. Other geometries will have different ratios.

http://www.audioasylum.com/audio/vinyl/messages/77287.html

BTW, the dimensions illustrated in this table vary a little from the ones provided my Micro Seiki for the MA-505 standard length arm (237mm, 222mm, 21 degrees 50 minutes) which uses a different geometry.

HTH,

Bill

Changing one of the three "dimensions" changes the other two for a given geometry. If the STP increases, so does the effective length, the cartridge offset angle shallows.

This only makes sense...

As P-to-S increases, effective length must increase (logically). Also, as P-to-S increases, overhang decreases and cartridge offset angle shallows.

Taken to the extreme (as P-to-S goes to infinity), the overhang goes to 0 (as P-to-S and effective length becomes equal) and offset angle goes to 0 as well. This is what a linear tracking arm attempts to mimic.

No thanks necessary for me pointing out the obvious. I'm here to help.

Raul,

The issue with the SME V is that the holes for cartridge mounting do not allow for any other cartridge position or adjustment of the cartridge in the headshell. This would be OK if all cartridges used the same "mounting hole to stylus distance." Bit there is no standard value for the position of the stylus relative to the mounting holes in the cartridge. Therefore, as the position of the stylus relative to the mounting holes changes, then so does the effective length of the arm. Since the effective length changes, so does the STP distance. Increase the effective length and the STP, and the cartridge offset angle must decrease.

So the geometry of the SME arm changes most every time there is a change of cartridge. In some cases, it seems that the cartridge offset angle will not be a good match the effective length / STP.

Even though we're talking about VERY MINUTE differences, I wonder if that might be one of the reasons that the SME V arm doesn't seem to perform as well for some users.

Bill

Dear Raul, If I understand the design of SME V then the designers assumed the exact position of the stylus in all
carts. Otherwise thy would make slots in the headshell.
The actual carts are some kind of 'movenig targets'in this
respect. So to get the right eff. lenght or those null points one must 'slide' the arm and consequently change the SPD. If I understand J. Carr correctly one should recalculate the geometry for the 'deviant carts'. BTW in some other models SME changed the headshell.

Regards,

There is a range of tracking errors that sound similar if not identical. (I would admit that with certain vinyl setups the differences may be more noticeable.) To provide some perspective: Given the gamut of alignments, including Lofgren A (Baerwald), Lofgren B, and Stevenson plus the myriad of "custom" geometries and alignments, each considered optimal to portions of the vinyl audiophile community, there is more than one "optimal" alignment geometry.

I use a SME tone arm and the differences in tracking error from one cartridge to the next are so slight that I do not worry about it. Some cartridges result in less distortion across the mid-section of the groove while others have less distortion at the beginning and end of the groove. I've learned to accept the range of alignments and would be hard pressed to detect the differences with many if not most records anyway.

So when we start to nit pick over the merits or disadvantages of specific modulated groove radii, null point radii, and nominal effective lengths, I believe we're teetering on the edge of being bumptious if not dilusional.

I would agree that certain combinations of cartridge and tone arm may not play nicely with certain alignments and that there are some cartridges with atypical mounting hole parameters that will not work well with fixed headshell offset angles, but within the range of typical cartridge and tone arm geometries there is a range of alignments that play and sound just fine.

Or not. :-)

TomTom