The Korf Blog

The inside story: our research, development and opinions

7 April 2017
The Test Arm Configuration
For the armtube comparison, I would not build a dedicated tonearm from scratch. Using parts from an existing arm is quicker, cheaper and does not introduce new variables and surprises into the test.

An OEM version of Ortofon AS 212 is mechanically simple, is known to sound good, has very few vices and is inexpensive enough to play with. I have a couple, taken from Telefunken S500 turntables. In my previous tonearm experiments I have used them to good effect.

The picture on the right is from the Ortofon page about this arm.

But AS 212 isn't perfect. Some things are less than optimal. Take geometry: first, its horizontal axis is perpendicular to the armtube, and thus the up-down motion introduces azimuth error. Second, the horizontal axis sits a lot higher than the plane in which the stylus rides. This geometry results in a slight variation of tracking force in relation to the LP groove amplitude. I will write about these geometric problems in a lot more detail later.

AS 212
The plastic part is marked 6 in the original Ortofon illustration
Also, I do not like the configuration of the part that holds together the vertical bearing, armtube and counterweight stub. It is a soft plastic thingy that has deteriorated with age. Replacing the arm tube without damaging it is next to impossible.

As you see above, the AS 212 has a JIS connector for a straight industry standard headshell. This requires a bent armtube that is difficult or impossible to manufacture in most of the materials we want to test. So I have changed the geometry to a straight armtube and an offset headshell, a la Linn Ittok.
These changes called for a new central part and a new headshell. Here is what I came up with. I am using Onshape cloud-based CAD for this project, and you can go check out the designs here.
To make sure the parts fit and the geometry is correct, I have sent the designs off to a 3D printer. Once I have the plastic parts and am sure they fit as they should, I'll order CNC aluminium ones.
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