Vintage DD turntables. Are we living dangerously?

Henry, As I now understand it, the 300 series Acutex's are induced magnet types (of that I am certain), but the later end of run 400 series cartridges are conventional moving magnet types.  So, it would not surprise me if they sound very different. I own a 420 and a 412, but I have never heard either one.  The LPM series has an optional "headshell", which word I put in quotations, because it does not look like a headshell, more like a P-mount.  This is called the "Saturn V".  The LPM320 has a compliance of 42, which makes it even more strange that it works so well on the FR64S.  Using the Saturn V mount with the LPM320 would reduce the total effective mass by at least 5-10g, so it may be worth trying to re-mount my LPM320 into the Saturn V.  (I've got one.) Based on a OEM compliance of 42 and an estimated effective mass of (FR64S plus DV505 headshell plus LPM320 in conventional adapter) at 30g, I calculate an expected resonant frequency of around 5 Hz.  Maybe this is cool, as long as the LP does not have a warp or the floor does not shake.  My best guess is that because the 320 is now pushing 30 years old, the compliance is reduced from its OEM value due to aging of the suspension, which may be working in my favor on the FR64S.

Either you or your machinist is very talented to have made that beautiful and probably effective mounting system for your TT101. Congrats.

JB, I am glad you are happy with the Krebs mod; I've been touting it for months after hearing how it positively affected my Mk3.  I was previously a skeptic. As far as I know, the mod is less expensive when applied to the Mk2 vs the Mk3, so doing it on a Mk2 is even more of a no-brainer.  Also, it will get even better over the first 20-50 hours of use.  At first, I was not sure whether I was really hearing it or whether it was partly my imagination and listener bias.  Then after 10 hours or so and counting, all self doubts evaporated.

Lewm, 


What does the "Krebs mod" consist of ?

Thanks in advance


Peter

No one really knows.  There's the rub.  The idea is to stabilize the stator (in the Mk2 and Mk3) so as to lessen the effect on the stator of torque inputs prompted by the servo sensing a speed inaccuracy.  The thesis is that very minor displacements of the stator due to torque input lead to spurious or unnecessary further speed corrections, which results in the colorations that some hear with the big Technics DD turntables. You want all the energy to go into the rotor (which essentially IS the platter). Newton's Third Law of motion says that there must be an equal and opposite force (torque) on the stator; the attempt is to cancel the effect of that force.  How this is achieved is a proprietary secret, apparently. Before I re-assembled my Mk3, after getting it back from Bill Thalmann who did the Krebs mod on it, I could easily see that "something" had been done to the structure around the stator, but nothing was obvious about it. Richard Krebs tells me privately that he experimented extensively before arriving at his solution, even ruined a Mk3 in the process, I think he said. I'm sure he's here somewhere.

I shouldn't have written that "no one really knows" the nature of the Krebs mod.  Obviously, Richard and Bill do know.  But they ain't talkin'.

My experience agrees with what Richard wrote about "run in".  As I wrote earlier, the differences were at first subtle and now obvious-er and obvious-er.