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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
sonofjim
557 posts
 
Sebastian,
No, I never changed anything about the mkll to use a CU-180. As far as adjusting speed on the mkll, I don't even know if it's possible. I'm not that technically knowledgable but there's no pitch control built in and the speed is quartz regulated. I liked what I was hearing with the Cu-180 but given it's weight, it made sense to me to use a lighter mat which theoretically should allow the platter speed control to function in a situation closer to what it was designed for. Both the mkll and mklll are overbuilt but the mklll much more so. The added mass of the CU-180 doesn't concern me on the mklll and pitch control is present though I've never needed it. I imagine the CU-180/mkll combination may work well without reason for concern. Readily available at about $200 though, the Boston Mat ll would be my top recommendation for the mkll. I'm just a guy who's used all this stuff and by no means an expert so take this for what it's worth.
lewm
13,248 posts
 
The speed can be fine-tuned, if necessary, by fiddling with the PS. I don't know for sure what is done, but Bill Thalmann can do it. However, if the speed is altered by substitution of a heavier- or lighter- than- stock platter mat, that would be one way to KNOW for sure that the mat is too heavy or too light. That symptom tells you that the change in the inertial mass has screwed up the servo mechanism.
pryso
1,941 posts
 
Sebastien, I've offered this information to another post with a similar question.

In the manual for my SP-10 Mk2A it states, "The quartz phase-locked control system and the DC motor with large torque can maintain each rated speed of the turntable even with a load torque of up to 5 kg-cm (4.3 lbs. in.). If 500 tonearms of 2 g. tracking force were placed on a record at the same time the turntable would still maintain the rated speed."

Visualizing 500 tonearms arrayed around the platter is a bit daunting. But I would guess the real question is what weight can be accommodated by the spindle bearing without undue wear over time, rather than what will affect speed performance?
lewm
13,248 posts
 
Tim, I know you have quoted that paragraph before, but just now I stopped to think about it maybe for the first time. 500 times 2 gm = 1000 gm. That's a bit more than half a pound. So, by this statement you might say that Technics authorized use of a platter mat that is about a half pound heavier than stock. That's still way less than the 4-lb weight of a CU180 or one of those TT Weights products. Of course, you may fairly argue, Technics was also saying the motor could overcome the stylus drag of 500 cartridges at that VTF. I don't know how to translate that into real world numbers.
lewm
13,248 posts
 
Sorry, 1000 gm = 2.2 lb. What a yutz I am!
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