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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
sebastienl
pryso
1,501 posts
 
Albert, I wonder if your objective in your plinth design was to "sink" vibrational energy rather than synchronize ("sync") it. But maybe synchronizing vibration frequencies for turntables is related to British thin-walled speaker cabinets? ;^)

But seriously, with Lbeichev's question, I might guess that Technics engineers did make their best effort to design a suitable plinth -- for that point in time. If one checks back they will see Technics designed and offered a total of four different plinths for their SP-10 series of motor units and three out of four increased mass over the predecessor. The point is that much has been learned since the '70s when there were designed and sold. Just look at developments over the last 5-6 years in rim-drive turntables (Garrard, Thorens, Lenco) and how their performance has been improved. I suspect the current interest in DD tables followed what was learned with rim drive units (meaning mass and stability).
sonofjim
557 posts
 
Lewm et all,
Sorry, I missed this thread initially. I have heard the SP-10 mklll with Krebs mods. In fact I have it in my system currently. I had some mechanical issues getting the table reinstalled in it's current Artisan Fidelity plinth but having resolved those it's running very quietly. I'm very happy with it's performance at this point.
I also have a mklll in a Dobbins plinth which has been my reference as far as silent operation is concerned. I would say the performance of the two tables is very similar at this point. It's hard to imagine better vinyl playback or machines more user friendly in everyday use.
Which would I recommend? Both. If carried out to their ultimate endpoint, both designs are reference quality in my opinion and a winner would be hard to chose. It may depend more on the look you're after. Hope this is helpful in some way.
albertporter's avatar
albertporter
4,927 posts
 
I will leave it to Audiogon members to decide who copied what. Take a look at ads and dates.
albertporter's avatar
albertporter
4,927 posts
 
Albert, Why do you think the Technics engineers were able to make the best turntable, but they were not able to design a suitable plinth?
Lbelchev (Answers | This Thread)

For the same reason Technics did not know to do the Krebs mods which raise speed stability and improve transparency and dynamics.

There are precious few products manufactured 25 years ago that cannot in some way be improved through modern materials and technology that simply was not available back then.
albertporter's avatar
albertporter
4,927 posts
 
Sonofjim (Kent),

I'm surprised that all the phone calls and email messages we exchanged you never mentioned the mods done by Bill.

Are you saying the two tables are almost the same performance (with and without) the mods?

Your tests certainly did not result in the same outcome as here. Also, Bill explained the issue you had with noise on the (non) Dobbins version of the MK3. That was a huge noise generator easily wiping out any benefit of the mods.
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