Victor TT 101 vs TT 81

Dear HWS,  Bill Thalmann's shop is about 20 minutes from me, and Bill has worked on my TT101, twice.  Bill has also worked (successfully) on several of my other DD turntables and on one of my Beveridge direct-drive amplifiers. But when my TT101 was in Bill's shop (last year), the problem was intermittent, and the unit worked fine, for 2 weeks, on Bill's workbench.  We could not make it fail over there.  In my house, it was working OK much of the time but would occasionally malfunction in a way I will describe.  In search of a cause, we (Bill and I) surmised that there was a bad solder joint somewhere. (This is after Bill had already replaced every electrolytic except one and also re-soldered many of the joints.)   At that point, Bill was understandably rather tired of fooling with it.  I am a fairly decent DIYer myself, but not with ICs and not so experienced with any sort of solid state gear.  However, in my spare time and because I have other tt's to use,  I went in there looking for possible bad connections.  I suspected that there may be a cracked wire going into one of the many beige-colored multi-prong connectors that connect different PCBs to each other.   Two in particular on the board that is tucked up under the top escutcheon, housing the servo mechanisms, seemed loose.  So I cut off the beige connectors and hard-soldered those wires to the prongs.  (Both are 4-prong connections.) Along the way, I also replaced the one electrolytic that Bill missed doing earlier; it sits alone in that servo board up under the top piece. 

The result of my labors was to make an intermittent problem into a permanent one!  Here is the failure mode:  The tt comes up to speed based on the tach reading "33.33", but very shortly thereafter, within less than a minute, you will see readings suggesting the speed is off, 33.32 then 33.34, etc, typically.  At that point, the motor shudders significantly and shuts itself down; the platter coasts to a stop with no brake action.  The tach goes blank, except for the decimal point.  That's the story.  This is what it used to do only intermittently.  I must say though that I had not detected the motor shudder symptom earlier, but that may have been because the tt was then bolted into a sturdy  and heavy plinth.  To work on it on my bench, I built a lightweight jig which enables me to flip it upside down easily without risk of damage to the innards.  The jig is supported only by 3 metal threaded rods, which is probably why the motor can shake the whole assembly. The bearing is dead silent throughout all this failure mode.  There is no rubbing sound or other friction noises.  My hypothesis is that the servo is failing in one of the two directions such that the correction mechanisms are fighting each other; that's how I explain the motor shudder prior to shutdown.

I have thoughts of taking it back to Bill, now that the problem is sure to occur in his hands.  He is a superb guy in all ways.  However, I thought perhaps you may have a guy who is steeped in servo technology who might provide some insight.

Hi Halcro,

Thanks for all the links you have provided.  Although I had read them in the past, it was good to revisit.  I was surfing the Vinyl Engine JVC turntable section and I came across the QL 66F.  One of the threads you directed me to references your experience with a lower QL version (A5??), and how it impressed you.  It appears the 66F was one of the last higher end tt JVC made.  I don't care for its automatic controls, but it seems its motor borrows much the TT 101's tech, even more than the TT 81 did.  The 66F also uses a coreless motor and servo controls.  Have you ever had a chance to examine one?  Reading a couple of threads on the net suggest that it benefits from a lot damping of the plinth.  Considering it probably does not sell for much on the used market, I wonder how difficult it would be to remove its motor and motor electronics to use elsewhere. 

Hi rgs,

In the Vintage DD Thread, there are some Posts by HiHo
https://forum.audiogon.com/discussions/vintage-dd-turntables-are-we-living-dangerously?page=12
who is very knowledgeable about all the Victor models made only for the Japanese market, and we discussed the QL66F among others.

You started this Thread asking about the ’sonic’ differences between the TT-81 and TT-101.
To me, there appears to be none.
If, as it appears now....you are wedded to a Victor coreless motor.....that’s another kettle of fish altogether and I would strongly recommend that you wait for a good TT-101 to come along.
Good luck...👍😎

Thanks Halcro.  You are right, initially I thought I would go with the TT 81 if it was the same, but I think in the end my bias towards coreless will reign.  TT 101 it is.