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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
lewm
12,524 posts
 
If EMI is a real problem, one could also make a shield expressly to treat that problem; the shield can be placed under one's mat of choice. I did exactly that for my Kenwood L07D, which uses a stainless steel platter mat, which you would think is by itself a decent shield. Nevertheless the L07D sound was improved by using TI Shield (a Texas Instruments product). I bought one square foot and cut it in the shape of an LP so it fits under the SS mat. Works very well.

What is the weight of the cu180? This is an old and pointless debate, but using a much heavier than stock platter mat in theory is not a good thing for a servo-controlled direct-drive, where the system was designed to cope with a certain inertial mass. Note, I say "in theory". I realize there are practical exceptions. And actually I think the cu180 is within shouting distance of the weight of the standard mat, about the same as the SAEC SS300, which I know does no harm on the Mk2. Not as crazy as some of those very much heavier TT Weights mats.
sarcher30
596 posts
 
Lewm, The cu-180 is 4 lbs. I had the same concerns about too much weight affecting the servo in a negative way. In practice this is simply not the case. If anything it's affecting it in a positive way.

I had some TI Sheild that I put under my Boston mat. TI Sheild is very springy stuff. If it's not perfectly flat it will not lie flat unless you have a heavy enough weight on top. The Boston mat is not heavy enough. A heavier mat negates any weight saving advantage. It is conceivable someone could get it flat enough to work but it's very difficult. I ruined the TI Sheild I had messing with it. I could get some more and try it under my cu-180 and see if there is any improvement.

Will your stainless steel mat from your Kenwood fit on your SP-10 mk3? That would be an interesting experiment. I believe Albert Porter is using a SS mat on his mk3.
sebastienl's avatar
sebastienl OP
84 posts
 
As I said above, I am considering the Micro-Seiki CU-180 mat from a seller who's serious and from whom I already bought. The seller tell me that the mat is brand new and was made in 2011. I'm a little bit surprised because I was sure that Micro-Seiki was not in the business anymore and this mat not in production for already few years. Is there some of you that can confirm the time that the production of the CU-180 ended?

Thanks,

Sébastien
sarcher30
596 posts
 
From what I found online it looks like Micro Seiki went out of biz in 2001.

It must be a copy.
lewm
12,524 posts
 
Dear Sarcher, If the CU180 weighs 4 lbs, I personally would to use it on a Mk2, as the stock mat weighs only about one lb. The whole platter weighs ca 8 lbs, I think. So by using the CU180, you increase the inertial mass by nearly 50%. But this is all theory, and if it sounds great, just ignore me.

Since the Kenwood L07D stainless steel mat weighs 5 lbs, you can bet that it flattens out the TI Shield "real good", to quote Big Jim McBob from SCTV. Flat as a pancake; you cannot even see it's there, because I cut it to be very slightly smaller in diameter than the ss mat. I hadn't thought about that issue you bring up in relation to using it with a lightweight mat. Further, the TI Shield has to be grounded in order to work as a shield; I am not sure it would be grounded if used under a non-conductive mat, like the Boston Audio products. Maybe so if the platter itself is bare metal, i.e., not painted or coated with something that insulates.

Albert is lately using the Boston Audio Mat2, on his Mk3. As mentioned above, I use the Mat2 as well on my own Mk3. We arrived at the same place coincidentally. I like the Mat2 a tad better than the SAEC SS300. By the same token, I would be reluctant to use the Kenwood mat on my MK3, because it weighs 5X the OEM rubber mat.

I got this notion about not violating the inertial mass of the stock design from, of course, something I read on the web. I have always meant to check it out with Bill Thalmann, who has worked on both my Mk2 and Mk3, but it does make sense.
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