Cartridge Setup / Alignment - Microscope Anyone?
 

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...

Josh.......I use a Bausch & Lomb glass 10X loupe.


http://www.cepeitalia.net/foto/341/178in082.jpg

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.

Thanks, jdandy!

tima - I was actually reading the Fremer article again last night before I posted this.

I've been using the Dr. Feickert Alignment Tool, but I've also read threads by you and others about the UNI-Protractor / SMARTractor. Perhaps I should continue to set VTA by ear and consider investing in one of those tools. Maybe I'll get lucky and find one on the used market - though it isn't likely!

Well, you can't set alignment by ear. :-) The first version of the Feickert includes a nice tool for measuring and setting P2S - I'm glad I kept mine for that reason. I found the actual alignment facility so-so. Have not tried his second (mirrored plastic) version. As far as Acoustical Systems goes, while I have the UNI-Protractor, based on price I'd go for the SmartTractor if buying today. But if you think the Feickert is doing a good job for you, then great. I believe one needs to feel comfortable using whatever tools.

Configuring a 3-D object in space (the stylus) is challenging, though the tools available today put us much farther along toward doing that in a repeatable way than were had last century. After P2S, VTF and alignment are, imo, most critical. I'd put SRA and azimuth on par with each other, as these depend somewhat on the cartridge. Different carts have different sensitivities, with azimuth more critical than SRA for some, and just the opposite for others. Of course both count. There should be enough info on the Web describing ways to set both using your ears. Let me know if you need info on those techniques.

Wally Malewicz sells a simple tool he calls WallyVTA whose sole purpose is getting your tonearm parallel to the record. That position should be the starting point for however you proceed with SRA. When experimenting I found it valuable to have a known baseline to return the 'arm to.