Greetings,
I go nuts when manufacturers won't divulge a simple spec. like effective length.
I've been trying to find this number for the Well Tempered arm for someone, and Well Tempered treats this number as if it were a military secret.
Don't these guys want their products to sound good? I consider an arc protractor to be an essential tool for vinyl playback and actually put up a dedicated page to Yip's product in my accessory section. I consider it to be be that important.
Rant off ...
How good are you at using a ruler? You can find a good enough working number for effective length for Yip to make you a protractor.
The easiest way to measure this is as follows:
1. Put a thin strip of masking tape on your headshell - between the two cartridge mounting slots and extending forward to the front of the headshell.
2. Move your cartridge midway (front to back) in the headshell slots.
3. Find the midpoint between the two cartridge screws and mark this point.
4. Measure forward of this point by 9.25mm (9 and "little bit").
This is the point where the "average" cartridge's stylus is located. This offset differs by manufacturer and is one reason for the slots in the headshell. The other reason is to allow for fine rotational adjustments to compensate for skewed cantilevers.
Now, measure the distance from the tonearm bearing pivot to this point where your virtual stylus is located.
This is your effective length, and all that Yip needs (other than your record spindle diameter).
Note, that a few of my customers have gotten confused by tonearms with offset mounts like your JMW, the Tri-Planar, and the Schroeder Reference. They mistakenly think of the center of the Tri-Planar's VTA tower knob as being the bearing pivot.
The with your JMW, this should be a bit more intuitive. If you remove the arm wand assembly and do this job on your desk, you won't inadvertently measure the distance to the VTA knob. It's too far away (grin).
As long as you're within 1 or 2mm, you'll be fine because you'll be able to compensate for various cartridge brands (having differing stylus offsets from the mounting holes) by moving the cartridge in the headshell slots.
Let's say you arrive at a 290mm effective length and later discover that the "real" number is 288. Don't lose any sleep. The difference is meaningless and don't let any "experts" tell you otherwise. As long as you align to a 290mm arc you'll be grinning ear to ear.
Cheers,
Thom @ Galibier
