The Korf Blog

The inside story: our research, development and opinions

2 July 2018
Second Flexure Prototype
First, the not so good news. Our reference Micro Seiki RX-1500 will remain out of service for quite a while. The main bearing will need to be re-lubed, and this means sourcing a special lead-based lubricant. It might take time.

The good news is, hearing of our plight, a good friend allowed us to use his TechDAS Air Force III to do our subjective evaluations. We couldn't possibly wish for a better turntable.

A couple of month ago, we started to investigate flexure bearings. We've built a prototype tonearm and ordered some laser-cut flexures. Then we've done some measurements that surprised us a bit. Now it's time for subjective evaluation and the measurement of different flexure springs.
The first prototype had carbon spring steel flexure. It didn't permanently deform under the weight of an arm, but then it failed rather suddenly. We replaced it with a stainless steel spring that behaved quite differently. Loaded with a full weight of an arm, it started visibly sagging in a few hours. Knowing I don't have much time left, I've decided to do the measurements straight away.

The stainless steel flexure started sagging almost immediately.
And here they are. There's also data for Prototype 5 with ball bearings and steel counterweight stub for comparison.
Please disregard the lower headshell resonance — I had to use a slightly different wax to attach the accelerometer, and the contact between the accelerometer and headshell turned out to be not as good as usual. I will try to redo the measurement with a proper wax when I have time.

Here we have the same nice and clean 6kHz headshell subharmonic as with our previous prototype. The main armtube and counterweight resonances seem to be slightly better controlled.

I have expected the two flexures to measure same or almost same. Interesting, but it isn't quite the case.

Subjective evaluation
First the spring steel flexure prototype.

The general character of ball bearing prototype with thick-walled steel tube remains, but there is a bit more smoothness and finesse.

Result: ★★★★☆

The stainless steel flexure prototype not only measured differently, it also sounds different. It has everything spring steel prototype has, plus more definition and more "palpability". I believe we're on to something here. This is the first "five-star" performance from our prototypes.

Result: ★★★★★



Flexures keep surprising us not only in measured performance, but also in listening. We still have a brass flexure to measure and audition — looking forward to it!
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