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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

Showing 9 responses by pryso

pryso
1,901 posts
 
Sonofjim, do you have more than one system set up? Your system photos show a VPI, but neither of your SP-10s.

I'm always looking for ideas/recommendations regarding the Technics.
pryso
1,901 posts
 
Lew, thanks as always for your info.

Not to start another war here but Bill's comments on the need to dampen vibrations seems to fly in the face of the advocates for "plinthless" installations touted in a different Audiogon Analog posting. ;^)

That makes me wonder, have you ever ask Thalmann his perspective on plinthless DD installations? Yes, that might be a redundant question.
pryso
1,901 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?
pryso
1,901 posts
 
Yes Lew, I realized and wondered about the same point after posting this time.

So not to put words in Technics' mouth, perhaps they were referring to the 500 tone arms just as an example. That was wild enough without suggesting 2,500 arms could track simultaneously at 2 g. each without impacting speed performance!

But it clearly states a load torque up to 5 kg cm.

Again, I might be more concerned with bearing wear over time than speed stability. But I'm not an engineer.
pryso
1,901 posts
 
Lew, while I'm certainly not an expert on the Micro-Seiki line, they did produce direct drive tables as well as belt drives. At least I can't find anyplace to attach a belt on the M-S DD-40 table and arm I have in house. ;^)
pryso
1,901 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).
pryso
1,901 posts
 
Technics SP-10 series plinths:

From what I've been able to find, Technics offered as many as five separate plinths (bases) for the various SP-10 motor units.

The one SP-10 I've seen (not quartz locked and no outboard PS) had a traditional wood box frame plinth. Quite lightweight and I don't recall seeing a model number.

The SH-10B3 was a 12 kg layered combination of Obsidian, rubber, and wood and offered for the SP-10 Mk II motor unit.

The Vintage Technics site lists a SH-10B4 at 5.2 kg and a lower price. I've not seen any other reference to it.

The SH-10B5 was 19 kg and all Obsidian. It was introduced along with the SP-10 Mk 3 motor unit. Technics engineers obviously felt a more massive unit was needed for the increased torque motor.

The last one offered that I found info for was the SH-10B7. It was also all Obsidian but weight was listed at 17.5 kg. I've wondered why this was slightly less than the previous model? This plinth was offered during latter production of the SP-10 Mk 3 and Mk 2A.

The dates for these plinths ranged from the mid-70s to early 80s. Obviously Technics engineers were attempting to make improvements through materials and mass as they revised plinth design. But that is not to say it is what would be designed today with 30 more years of engineering knowledge and material choices.

If there was a change with the SP-10 Mk 3 motor unit frame (or chassis as Lew calls it) I would be interested to see a reference to that. I've never see a Mk 3 but own a Mk 2A.
pryso
1,901 posts
 
Hi Lew,

Now I'm confused. What I'm asking about is the cast metal frame that surrounds the platter, and in the case for the Mk 2 and Mk 2A provides support for circuit board attachment from underneath. Since I've never seen a Mk 3 except in photos I'm not sure about it. But from the top it appears identical to the Mk 2 and Mk 2A. This is what I understood you to mean by chassis.

The Vintage Technics site, which of course is not infallible, states the SH-10B7 plinth was intended for both the Mk 3 and Mk 2A mounting. The opening in that plinth is indeed not round. See this from Vinyl Engine -

http://www.vinylengine.com/library/technics/sh-10b7-obsidian-plinth.shtml

What I'd like to know is if the cast metal frame for the Mk 3 is different from the Mk 2A? That is, were additional vibration damping methods applied?
pryso
1,901 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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