[tima]

Originally Posted by livestrong

Is anyone using a microscope to help set the rake angle? It seems to be one of the most critical pieces of cartridge setup / alignment, yet one of the hardest to actually measure/set. Would love to hear if anyone has any experience with this - I'd like to properly setup my new Sumiko Pearwood Celebration II cartridge the best that I can!

Would love to hear if anyone here has any recommendations...

I'm assuming you're talking about using a USB digital microscope rather than trying to eyeball small differences in degree. Such a tool can help get you close to the somewhat theoretical SRA (stylus rake angle) of between 91.5° and 92.5°. In the end you'll still need to listen (trust your ears) to get things optimal, but a 'scope can get you to a starting point for that.

Here are things I've encountered using a USB digital 'scope to measure SRA:

- Before using a 'scope, make sure the pivot-to-spindle distance is per the tonearm specs and the cartridge alignment is as perfect as you can get it.

- Before using the 'scope make sure you've set VTF (vertical tracking force) where it needs to be. Then after any adjustments for SRA, check it again and adjust as needed.

- I remove any anti-skate force before measuring SRA.

- Decent microscope resolution is important: 2MP or 1280x1020 is okay.

- The lens of the 'scope on many designs needs to be very very close to the stylus to obtain proper focus. On the oft-chosen Dinolite models that means removing the plastic lens protector is necessary to get close enough.

- Absolutely critical is a decent stand that allows positioning the 'scope near the record edge and holding it steadfast. (You can not do this by hand.) You will adjust the position of the scope in the stand to obtain best focus on the stylus.

- Since many of these 'scopes' lenses are round, it is important to position the lens such that the surface the stylus sits on is at 0°. Placing a lined white index card behind the cartridge can help establish a baseline.

- The 'scope should be one that comes with measuring software that can be used on the snapshot of the stylus, or some alternative software that can draw lines and do angle calculations from them. I'm vaguely recalling Visio has such a function, but I haven't used that.

- Using the drawing software can be tedious and prone to inaccuracy. If you're off by a pixel when tracing the edges of the stylus, that can change the angle calculation. The clearer the picture the easier that is to do and is the reason why a high-resolution 'scope is helpful.

- Measure the angle of each side of the stylus relative to the surface. Start with 180 degrees, subtract the first measured angle, add the second measured angle and divide by two.

- Adjust the SRA according to the abilities of your tonearm. Then measure again. A 1° change on a 9" 'arm means a 4mm height change at the 'arms pivot end.

Credit for much of the work on this measurement technique goes to Wally Malewicz and was publicized by Mike Fremer. The number of 92° comes from an article (PDF) by Jon Risch and Bruce Maier.