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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
sarcher30
596 posts
 
Sonofjim, Thanks for your input. I have changed back and forth a couple of times between the cu-180 and BA-1 and still prefer the cu-180. Maybe I should try the BA-2 one of these days.

Lewm and Sonofjim, Do either of you guys plan on having Bill Thalmann do the latest mods on your MK3 like Albert Porter has recently done? I wonder if Albert has changed his prefence of mats after the mods were completed.

Sean
lewm
13,362 posts
 
Sarcher and Pryso, 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. Everything gets even smoother than it was. There is also some work done inside the PS, about which I know nothing. Anyway, Albert likes. I will get it done, but the cost is $1200, so I am waiting a bit before I can commit those bucks.
sarcher30
596 posts
 
Lewm, Cool. Thanks for the additional info on the mod. I understand Bill is working on introducing a similar mod for the mk2 according to Albert.
lewm
13,362 posts
 
I think the Mk2 mod can be had also, at this time and for much less cost.
pryso
1,956 posts
 
Lew, thanks as always for your info.

Not to start another war here but Bill's comments on the need to dampen vibrations seems to fly in the face of the advocates for "plinthless" installations touted in a different Audiogon Analog posting. ;^)

That makes me wonder, have you ever ask Thalmann his perspective on plinthless DD installations? Yes, that might be a redundant question.
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