Pickup SRA - starting from a 500x microscope

Hi O_holter. Sorry for not having seen this thread previously, and many thanks to the forum members who pointed it out to me. I very seldom visit this forum, and would not visit the Amps Preamps forum in the expectation of finding threads specifically about phono cartridges.

There have many threads about this same topic, and not only on Audiogon. For example, this one.

http://www.whatsbestforum.com/showthread.php?536-The-importance-of-VTA-SRA-and-Azimuth-pics

I have made relevant posts on page 13 and 14, maybe more.

FWIW, I know for a fact that LPs are not all cut at the same SRA, and the stylus used to cut LPs, being made of sapphire rather than diamond (for noise reasons), doesn't last very long. The chuck used to install the cutting styli allows a certain amount of freedom in adjusting the angle and how much the stylus protrudes, and not all cutting engineers have the same preference. Nor are the cutting stylii all made the same.

I have been told that that cutting engineers usually go for the setting that gives them the cleanest and quietest cut (test lacquers are usually cut before the real one). The cutting temperature also affects how easily and cleanly the stylus goes through the lacquer, so a number of interdependent variables are involved. Whether this results in a final cutting SRA of 92 degrees or not, depends on the cutting engineer, the individual cutting stylus, the lacquer blank, the master tape signal content (how much ampliftude, how much deep bass etc.), and more.

I also know that the photos of the same cartridge have been sent to the same expert on separate occasions (sometimes the same exact photo), resulting in different opinions on the SRA (too low, too high, just right). Undoubtedly visual assessment of SRA leaves room for individual interpretation (even by the same person).

The Lyra cartridges are made to deliver their best sound when the cartridge body is parallel to the LP. However, each cartridge has a slightly different optimal VTF (which changes according to the ambient temperature), and the proper VTF is critical to getting the cantilever rake angle and SRA right. At rest (no VTF applied), the Lyra cantilevers are designed to deflect downwards by about 3 degrees. Applying the proscribed amount of VTF (1.75g or thereabouts) should reduce the cantilever angle to 20 degrees, and the SRA to about 92 degrees. The recommended VTF range is only - +/- 0.05g, and this tight range is necessary to properly dial-in the cantilever, stylus and coil angles.

Today's tonearm designs pretty much guarantee that VTF will change as a function of the VTA adjustment mechanism. I trust that those who experiment with SRA are meticulous enough to check the VTF after each SRA adjustment, and readjust the VTF if it has changed? Note that the effective tonearm length and overhang will also change when the VTA mechanism is adjusted; these should also be remeasured and reset, otherwise the change in sound could be due to different VTF and different overhang together with SRA.

I don't think that the audiophile community (as well as tonearm and cartridge manufacturers) is yet at the stage where targeting a specific SRA angle is sufficient for optimal sound. I still think that it is best for audiophiles to adjust by ear, using the cartridge manufacturers recommendations as a starting point, hopefully re-check and re-adjust the VTF and overhang while the VTA adjustments are proceeding, and then use microscopes to find out what the SRA became. Put 10s or hundreds of such measurements into a database, and the information should begin to approach some semblance of validity that cartridge manufacturers can act on.

I also think that today's single-minded obsessiveness with SRA sends out the wrong message to cartridge manufacturers, because along with it comes the idea that cantilever rake angle does not matter as long as the SRA is 92 degrees. Although this is a case of reductio ad absurdum, there are cartridge models on the market with measured cantilever rake angles that are all over the place.

http://www.vinylengine.com/turntable_forum/gallery/image.php?album_id=97&image_id=16471&view=no_count

http://www.vinylengine.com/turntable_forum/gallery/image.php?album_id=97&image_id=16472&view=no_count

In reality, the vertical compliance of the cartridge increases in stiffness as a function of higher cantilever rake angle (calculate the sine of the cantilever rake angle), while the horizontal compliance does not change. What the cartridge should have is equal compliance in both the vertical and horizontal directions, and for this lower cantilever rake angles work better.

kind regards, jonathan

Hi Ralph: No, I missed that post of yours, but it is a good one. Much of my knowledge of the LP cutting process comes from Takawa-san and his boys who were responsible for all of the King Super Analog series, and also Joe Harley, who has produced many a LP, but it is nice to be able to check my information against yours.

Guys, Ralph owns and operates an LP cutting lathe, and when he writes something about LPs and the LP mastering and cutting process, his words are based on first-hand experience!

BTW, I have absolutely no desire to dissuade anyone from using a USB microscope. As a firm believer in the importance of correlating objective measurements with subjective listening impressions (or at least seriously trying), I strongly encourage the use of azimuth checkers, digital scales, USB microscopes and anything else which can attach numbers to what we hear.

My prime suggestion in this case is that the ear be used as the principle guide, and the microscope used to translate the optimal setting into numbers that can be replicated or independently confirmed.

I'd love to see a database containing the SRA findings of hundreds of audiophiles. The greater the number of SRA reports, the more the outlier cases will be down-prioritized, leading to more meaningful results for us cartridge manufacturers. It would also be nice to have cantilever rake angles (which the microscope software should be able to supply) as well as the SRA, since the cantilever rake angle must also affect how the cartridge responds to the LP groove (as I wrote in my previous post).

kind regards to all, jonathan

Hi O_holter. When you raise the SME pivot by 6-8mm, you are not only changing the SRA, you are also increasing the VTF, and reducing the overhang along with the tonearm effective length.

In order to isolate your findings to SRA only, you need to compare the VTF before and after raise and add the difference in VTF to the before raise position, or subtract the difference in VTF from the after raise position.

Also, you need to quantify how much the stylus position has moved and either pull the Atlas back a skosh in the before raise position, or nudge it forward a skosh in the after raise position.

I am not poo-poohing your findings at all, but good science demands that only one variable is changed at a time - even though you will have to fight the tonearm design to accomplish this.

Once you have confirmed the above and hopefully pinned the reason for the sonic improvement down to SRA increase and nothing else, I would be very interested in knowing what SRA and CRA (cantilever rake angle) your USB microscope reveals.

kind regards, jonathan