The Korf Blog

The inside story: our research, development and opinions

4 October 2018
Arm Tubes Revisited — Prototype 11
Last December, we've completed our experiment with various arm tube and arm wand configurations. However, a month or so ago I came across some new materials that made me want to go back and do a few more measurements. To say that the result surprised me would be an understatement.

Prototype number 11 is ceramic. Recrystalised Alumina, to be precise. It has an outside diameter of 10 mm and the inside one of only 6 mm, so it's quite heavy. At 35 grams, it's the heaviest of all we've ever measured.
It was quite difficult to balance such a heavy tube. Eventually, the heaviest Lenco counterweight we had plus a couple of stopper rings did the job. Ugly, but it works.

For vibrometry, we have a very rigid Prototype 5 (steel tube with 0.5 mm walls) and a carbon fiber Prototype 6 on the chart for comparison.
No significant surprises here, other than some strange high frequency hash I've put a blue frame around. Don't know what that is, probably some kind of reflections.

In all other aspects, it measures just like a steel tube. Counterweight peaks are a bit different because our counterweight arrangement is, ahem, "different". I thought the ceramic tube would be stiffer than the steel one, but no — it's about the same.

Subjective Evaluation
Onto the TechDAS it goes, and... What a surprise!

I don't know what impacted the sound more — the sheer mass of the resulting tonearm, or any specific qualities of recrystalised alumina — but the result is absolute magic. So much better than anything we've built so far.

I liked the arm so much that the prototype stayed on the turntable for a few days. It had all the positives of Prototype 5 and Prototype 6, plus the authority and stability only the best tonearms can achieve. The stereo image, while not larger or broader, was very sharp and accurate. Timbrally, all the richness a humble AT7V cartridge could extract was preserved.

Result: ★★★★★

As a side note, this prototype seems to confirm our findings about the low-frequency behaviour of tonearms. A very heavy tonearm with a relatively compliant cartridge should've had at least some problems, right? Skipping on warps, perhaps? Nope, Prototype 11 tracked as well as the lighter arms, if not better.

Might it be possible that most tonearms are simply built way too light? Please tell us what you think!

Can't really say now what will be the subject of the next post, because we have so much going on. Measurement of turntable main bearings? Entirely possible. A new flexure bearing tonearm? Can be, too. Yet another armtube material? Can't rule that out. Please subscribe to make sure you'll always get the updates!
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