Korf Blog, getting deep.......

[BillWojo]

http://korfaudio.com/blog95

Alex Korf's latest blog on direct drive tables is a bit out there. I posted a link to it on DIYAudio forum and it was also posted in VE. I usually respect what he has to say although I don't always agree 100% but this post is pretty far out there.
The graph near the end showing a "top quality late 1970s Japanese DD turntable", his words, is showing speed irregularities from 32.4 RPM to 34 RPM!
He also claims that there is major flux leakage from the DD motor that is causing issues with cartridge's.
The only thing I can think of is that Korf want's to introduce his own table and is trying to discredit any DD table like the British press did.
It's a shame, I used to look forward to his blog entry's to see what he was working on. Now, not so much. Seems he has an agenda.

BillWojo

 

[Colin86325]

Hi Bill, thanks for linking the article. Like you, I enjoy reading the Korf blog. I'm puzzled by the speed variation cited for "top quality" DD table; I suspect something was wrong with the unit measured.
A good way of representing speed variations is through a "polar plot" aka "radar map." Where the speed is represented as a ring as it tracks though 360 degrees. Speed variations are shown as deviations from a true circle. I think this is a far better way of displaying data vs a histogram/bar charts.

As an aside, I recall seeing something on the L-07D page he links, where an owner reported an improvement by using something like a mu-metal shield under the patter mat. I had pondered trying the same, or looking into adding powdered Nickle to a resin and pouring that in the underside of my platter, where it would add mechanical damping and magnetic shielding--assuming powder dispersed in a resin would work for that. But haven't gotten around to that. I don't have any issues with magnetic flux that I'm aware of, but it sounded like a fun project to try anyway...

 

[gadget73]

yeah that much speed variation seems strange to me. If he was able to measure it, why was noone else able to measure this 30-40 years ago?

 

[Mark 1234]

Something was definitely wrong! I have three Denon DP80's and the worst I have seen them after tons of measurements is 33.28- 33.4. It stays the same even with a really heavy record weight or a lighter one.

 

[MX117.MC7150]

Yes. Looking forward to his next blog to see what other past century DD ills he uncovers. His 'flux interference' is starting to smell.

 

[mr_petit]

As an aside, I recall seeing something on the L-07D page he links, where an owner reported an improvement by using something like a mu-metal shield under the patter mat.

...
I don't have any issues with magnetic flux that I'm aware of, but it sounded like a fun project to try anyway...

MM/MI cartridges are already cased in mu metal (if they are designed well)
MC cartridges have virtually no issue with this.

Too bad this Korf blog is also filled with assumptions and (wilfully?) missing data, (wilfully?) missing measurements, undefined statements and terminology and unnecessary comparisons that say nothing and are impossible to prove or disprove.

 

[kbwhaaland]

Well. It is a blog, folks, and AK is after all selling stuff.

I find this interesting:

The speed was taken 5000 times a second with a proprietary contactless Korf Audio system

This should, if I'm not completely off, make it possible to measure speed fluctuation frequency peaks as high as some 2400 Hz.

 

[Beobloke]

Has anyone with a functioning pair of ears ever actually referred to the Kenwood L-07D as "sonically mediocre"?!

As far as I can see, there's a flaw in his assumption about the effects of the motor's magnetic field on the cartridge. The flaw in question is circular and 33cm in diameter...

 

[jrtrent]

Alex Korf's latest blog on direct drive tables is a bit out there. I posted a link to it on DIYAudio forum and it was also posted in VE. I usually respect what he has to say although I don't always agree 100% but this post is pretty far out there. . .

I've never heard of Korf before, so thank you for the link. I think I'm going to wait to see the expected future blog entries on direct drive turntables before deciding how far out there or agenda-driven their treatment turns out to be.

 

[tabarddn51]

Hi, I have a highly refurbished Lenco 78 & a SP15, with the same 12'' arm & cart (not easy to set up, but can be done, because I did) I can not tell the T/T's apart. Theory is all very good, but if it cannot be heard then it becomes academic.


Cheers

 

[adnick]

None of my tables hit 32.4 rpm, that includes a DD, it would be immediately apparent. No need to sample speed 5 x and/or 5000 x per second when it’s slow

Now in a protracted time sampling, say an hour, I could believe an average that was + or - 33.3 rpm, it’s actually fairly interesting to do a 20 min speed test….

VR
Andy

 

[mr_petit]

None of my tables hit 32.4 rpm, that includes a DD, it would be immediately apparent.

yeah to me that also looks fairly impossible.
That would immediately show up on a strobe ring, and for people who claim that that variation could be really fast and not detectible by eye: that would require a lot of energy to drop and speed up again at that speed, and would also be almost impossible to do without an overshoot. It's a bold claim when using a "proprietory system" that is not shown or explained in any way and no raw data is published.