The Korf Blog

The inside story: our research,
development and opinions

10 September 2020
Alex, What is Taking You so Long?
An engineer friend of mine has recently discovered this blog. He scrolled all the way back to April 2017 and exclaimed: "What's taking you so long? The tonearm is just a stick on a gimbal, go sell one already!"

Today, I'll show you another small glimpse into why the high performance tonearm isn't just a stick on a gimbal. And why building one that we could be proud of takes some serious time.

The common tonearm-side SME type receptacle for the headshell is usually quite simple. It consists of the housing, the isolator, four sprung pins and a locking collar. The housing is usually attached to the armtube with one or two tiny screws. This description covers about 90% of all removeable headshell tonearms ever built.

The slightly better arm designers realize the importance of coupling the housing to the armtube. Quality arms can incorporate the little flat spring that takes up the slack between the housing and the inside of the tube. I had one but lost it, so we'll have to do without an illustration.

A typical commercially avialable SME-type headshell connector
Early on, we've decided that both approaches are not for us. We'll need something a lot more rigid and sturdy. Eventually, we've settled on a press-fit housing. It's located in azimuth by the pin that goes into a slot in the armtube. There is a screw too, serving as a second locating point and a check on correct positioning of the isolator inside the housing.

Yes, this means that azimuth adjustment by rotating the connector in the armtube is no longer possible. Don't think this loss should be lamented. This approach is just too crude, and I simply can not accept the resulting loss of rigidity.
Everything is, of course, custom-made.

The housing is high strength steel instead of the more usual aluminium. The gold-plated pins are continuous, having no break in them. The isolator is 3D-printed (laser sintered) out of nylon. The production versions would have either PTFE or PET isolators. In fact, the only off the shelf parts are the springs under the pins.

This is the approach we take with all the parts of the new tonearm. We design to requirements, instead of trying to fit off the shelf parts. This takes time: even the antiskating mechanism has custom magnets in it. The search for a manufacturer who could precision bend and cut some slots in a thin wall seamless steel tube is worthy of a separate post.

I can only hope that once all the parts are in place, the results would speak for themselves.

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