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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
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albertporter
4,949 posts
 
Bury the hatchet would be to drop the subject since my last reply was short.

Additional short answer is my plinth has no relation to the stock Technics plinth other than the radius around the perimeter.

Your's on the other hand copied our iron block and rod, recessed chassis, arm board design, rubber grommet and plate outlet for umbilical cable, metal interior plate sandwich to Panzerholz and pretty much all interior and exterior dimensions.
lewm
13,110 posts
 
Dear Tim, I think my original response does address what I think is your question. From the top side, the Mk2 and Mk3 "chassis'" are indistinguishable, as you suggest. What I was describing is that the part you don't see when the two are installed in any plinth is very different from one to the other. The SH10B7 plinth may indeed work with both units, but if you use the Mk3 in an SH10B7, there will either be empty space where the circular shape of the Mk3 motor housing does not conform to the square shape of the Mk2, OR there may have been a factory supplied insert that makes the SH10B7 fit the Mk3 snugly. Since Albert is among us, I need not speak for him, but I believe his plinths made for Mk2 can be adapted to Mk3 by adding some sort of wood inserts, or so it seems from one photo I once saw. Perhaps AP will comment.
catastrofe
87 posts
 
Albert, move on man. Continually bashing your competition reflects more poorly on you than it does on them.
lewm
13,110 posts
 
Tim, I should have added that because of the drastic difference in shapes, a plinth custom-made for a Mk3 would not fit the submergible portion of a Mk2 chassis. It's a square peg into a round hole, where the side of the square is at least the same as the diameter of the hole, and maybe bigger. Vice-versa mismatch would "work", as described.
pryso
1,933 posts
 
Lew, thanks for your clarifications.

I think I should have approached my question a little differently.

Since I have a SP-10 Mk2A I'd be interested to hear from anyone who modified their Mk 2 chassis. Since the number of Mk 2 and 2A (same chassis I'm sure) so greatly exceeded the production of Mk 3 motors it seems reasonable there might be more interest in Mk 2 and 2A upgrades. I'm not interested in going to the extent of eliminating the chassis and mounting the platter/motor directly to a plinth but if performance upgrades (reduced resonance) can be achieved by chassis modifications (damping) I would like to hear about specific recommendations.

Thanks.
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