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Technics SP-10 mkII speed adjustment question

Hi,

I'm on my way to complete my Technics SP-10 mkII project. Actually, a friend of mine, a professionnal audio technician, is working to upgrade the PSU, which is done but a small adjustment on the speed must be done and he need some cue on this issue.

We already asked Bill Thalmann, Artisan Fidelity and Oswald Mill audio. Plus, I'll post on DIY Audio today. We'd like to get the answer as quickly as possible to finalized this for the week-end. Hope someone on Audiogon can help.

Here's the message from my technician:

"Hello,

I'm an electronic technician and I do repair for audio equipments, vintage, hifi pro and more. I have a client here that brought me his turntable Technics Sp-10 MKII to fixed. I have a little question about it and he gave me your email because he pretended that you have some experience with this kind of materiel. So, hope that you can response my technical question.

I replaced all capacitors in the power supply and a big solder job. I checked for defect solders or capacitors on the circuit boards inside the turntable and I tied to do the adjustments . Everything seem good right now, the turntable work fine. I tried do do the period adjustment with the VR101 and VR102 potentiometers like in the service manual ( see attachment, Period adjustment method). When I looked the stroboscope at the front of the turntable, It's pretty stable but I can see a tiny rumble at 33 1/2 and 78 speed. 45 is the more stable speed for the stroboscope. So, I fixed the phase reference with T1 at 18us of period and I try to do the period adjustment at the point test T and S on the board with the O point for reference. When I put my scope probe on the T point, I can observe the stroboscope running. It is not stable at all. If I pull off my probe, the stroboscope is stable again. So When I have the 2 probes at point S an T at the same time to do the adjustment, it's impossible to fixed the wave T because it going right to the left on my scope. When I turned the VR101, the T wave going faster or slower but never stable. I tried to ground lift my scope, plug it into the same power bar and try to pull off the reference at the O point. I can't have a setup that I can see a stable T wave in my scope with the one that I can do the right adjustment. Why? Is there a problem with the turntable or maybe it's a incorrect probe or ground setup? Please let me know what you think.

Best regards"

Thanks for help,

Sébastien
128x128sebastienl
dover
2,251 posts
 
Lewm,
"With the modification to the stator mounts, there is less energy dissipated in moving the stators, more precise speed correction by the servo, and far fewer events that trigger the servo. Everything gets even smoother than it was."
But you questioned whether I could hear the error correction on the DD's, even on the "inventor" of these SP10mkIII mods system whose TT I have heard and am underwhelmed.
Halcro,
You need to denude yourself and go and sit on a crowded beach. Open your mind up. It seems clear to me that the gist of the suggestion was the amount of error correction could be reduced by providing a more stable mount for the stators or whatever. If you hear a difference from the removal of extraneous bits, as you proclaim, then why could there not be an improvement from altering the structure or support of those extraneous pieces and other essential components. Your use of referential authority in dismissing Lewms suggestions is not a persuasive argument. I sincerely hope that if you have had design input into bridges in Oz that you have considered the ground upon which they sit. I do have some dear friends over there.
Yo
lewm
13,174 posts
 
Dear Halcro and Dover,
I am trying to reconstruct each argument.
Halcro, you seemed to infer, back a few months ago, that a plinth cannot have much effect on structural rigidity of the Mk3, because of the way its spindle/bearing housing is supported within the chassis proper. Ergo, Newton and his 3rd Law go out the window. Is that a fair re-statement of your thesis?

Dover, It seems you are supporting my side, but you are also arguing with something I may have written earlier about whether you can hear the speed correction going on with a servo mechanism. Did I say that? Have you really heard the very same Mk3 that was originally modified a la what Bill Thalmann has recently done with Albert Porter's Mk3? (Bill did tell me that part of the cost of the modifications is due to some financial arrangement with their inventor.) And are you indeed saying you disliked the sound due to an aberration you attribute to audible action of the servo? I hope I was not so presumptuous as to say you cannot hear what you say you hear. I do hear a slight coloration with a fully serviced SP10 Mk2, but I cannot necessarily attribute it to servo action. However, I hear no coloration at all, or less than with any other tt in my memory, with a similarly prepped Mk3, in my slate and wood plinth. That's just me reporting my own observation, not gospel. Your re-statement of my description of the effects of the latest mod to Mk3 (and Mk2, if so desired) is spot on, by the way.
sebastienl's avatar
sebastienl OP
84 posts
 
Hi Lewm,

Regarding the modifications discussed above:

"Albert is ecstatic about the new modifications, but he really did not know much about what was done. I then talked to Bill about it. Mostly it is about dampening vibrations and firming up the stator supports. Bill notes that as the servo system corrects for speed errors, some of the energy of the motor is used up in micro movements of the stators, predicted by Newton's Third Law (For every action, etc...) (Ideally, all motor energy would go into moving the rotor/platter.) These tiny wiggles of the stator then in turn produce a tiny correction error sensed by the servo, which senses the fact that some of the torque went into moving the stators instead of the platter. This begets another correction from the servo. And so on. With the modification to the stator mounts, there is less energy dissipated in moving the stators, more precise speed correction by the servo, and far fewer events that trigger the servo...."

Do you know if you can do them on the SP-10 mkII?

Sébastien
lewm
13,174 posts
 
Bill can do it for the Mk2 as well. In fact, for some reason the cost is much less vs the Mk3. Ask Bill.
sebastienl's avatar
sebastienl OP
84 posts
 
Ok, thanks Lewm.
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