Technics SP-10 mkII speed adjustment question


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:


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,

Lbelchev -
Why do you think the Technics engineers were able to make the best turntable, but they were not able to design a suitable plinth?
I think the answer to your question is probably explained by the end use of the product. The Technics was primarily going into radio studios - hence the drop into a top plate/plinth makes sense. Conversely the Kenwood L07D and Exclusive P3 were primarily intended for domestic use, they did not have to consider dropping their TT into a DJ or studio worktop.
Kudos to Albert and others for generously sharing their knowledge with us.
Albert is on the money with product improvement. I think in the 70's cost was no object , but since then knowledge shared ( internet ), new materials and the lower cost and portability ( no pun intended ) of CNC machines means that the opportunity is ripe for re-engineering improvements at relatively modest costs.
Conversely we are in the age of mediocrity, convenience & cost cuts and some things are worse and were better built back then. Many materials due to shortages of trace elements and health & safety police have declined in quality.
I apologize. I'm not saying that the performance was the same before and after the mods. I'm saying that the mklll with Krebs mods and the Dobbins style direct mount produce similar results. Yes I had issues with rubbing on the chassis and even sent the table and platter back to Bill after the mods. He ran it out of the plinth for two weeks without issue. When I got it back I was more careful putting it back into the plinth to make sure it sat flat and not over tightening anything. I now believe the chassis was torqued or slightly twisted when the rubbing was occurring. It now run very quietly rivaling the direct mount in silence.
To me this is a question of eliminating noted or perceived performance issues with the original table(direct mount) or mitigating these issues with modifications, band-aides if you will. In my experience the band-aides are quite effective. I think it makes sense because both methods address the same issues.
I do agree that ANY rubbing or friction completely eliminates the benefit of the modifications which is why I went to such lengths to figure out the problem. Kudos to Bill for going the extra mile to address that.
I don't want to offend or argue with anyone. I've worked now with all three major plinth makers to good end. No single product has been perfect in every way but all work very well with tweaking. That's the nature of these vintage machines. The headache of getting them maximized is rewarded in the end. It's been a long journey for me but I finally seem to have reached a satisfying end point.
Dear Sonofjim, Thank you for your detailed response. I am treading on "little cat feet", but I have come to understand that a Krebs-modded Mk3 in a Dobbins plinth would not be too much of a good thing. Mr. Krebs was kind enough to send me some photos of his personal Mk3, and it is sitting in a Dobbins-type set-up, i.e., the motor is taken out of its chassis and directly mounted into his plinth. Likewise, I would guess that a Krebs-modded Mk3 in a Porter plinth is pretty fantastic. But I had no intention of starting a controversy about after-market plinths.

IMO, the difference between now and 25 years ago is mainly the zeal with which those of us in the here and now are approaching the art of playing a record. There was not much of a market for such craziness back then, except the tiny niche occupied by Merrill and a few others. Suspended tables with flimsy plinths, a la Linn, were also more in vogue back then. Fashions change with time. Remember the Woody Allen movie "Sleeper", where he wakes up after 200 years to find that steak and ice cream sundaes are health foods?