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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
 
12-09-12: Lewm
I guess I will ask another question and also bump this thread. Albert, did you have any truly objective way to know that the Krebs mods made a significant improvement in your Mk3's performance? Or are you reporting a subjective impression, which is perfectly OK?

I've had several MK3s. Two here now, one of which is beyond totally restored and for sale here at Audiogon.

When my MK3 got the electrical upgrade from Bill Thalmann the Krebs mod was not available. I had hundreds of hours to listen since my first MK3 and I've tested over and over the effect of plinths, mats, clamps, damping, isolation and tonearms.

My Krebs mod was gotten to quickly as mine was first in line. We still had the other table here as well as my ultimate reference of Studer tape and collection of master dubs.

The first 30 minutes with Krebs mod was such a surprise I could not take in the experience. Not that it was difficult to hear the difference, quite the opposite. My shock was the AMOUNT of difference this made.

I'm going to go out on a limb but the Krebs mod might be a bigger upgrade than going from Technics MK2 to Technics MK3.

As time has passed the upgrades improved. I know why since I have some knowledge of what is involved. However, unless Richard chooses to share "why" I will not go into that.

Based on the massive copy cat designs fostered by my Panzerholz plinth (soon to be 5 years ago) I can understand why Richard and Bill might be mute on the topic.
dover
2,247 posts
 
Lewm et al,
If you look underneath your Kenwood L07D you will find the archilles heal of the Technics SP10mk3.
lewm
13,110 posts
 
Dover, I think I know what you mean. The L07D represents a very different approach to direct-drive, compared to the Technics one. IMO, the L07D is vastly under-rated compared to the Mk3, which is not to say that the latter is not superb.

BFalls, I responded to your Audiogon message. Evidently you did not receive it. Audiogon may not want us to talk privately.
dover
2,247 posts
 
The Technics SP10mk3, Victor TT-101, Denon DP80 are all what I would call upside down turntables. That is they are designed to drop into plinths and the motor/mainbearing assembly hangs like dogs balls below the plinth - waving in the wind. The connection points to the "plinth" are on a flimsy exoskeleton/cover into which the motor/bearing are screwed.
The resultant structure lacks rigidity and the path for energy dissipation from platter to ground is compromised. Its a labyrinth from the platter to the ground, and the unstable reference of the tonearm to platter is counterproductive in measuring the groove accurately.
Compare this to the Kenwood L07D, where there is a massive cast foot underneath onto which BOTH the motor/bearing AND armpod are BOLTED.
see
http://www.l-07d.com/plinth.htm
This is a far superior construction in my view in maintaining rigidity between the arm/platter and the platter/turntable/arm/cartridge loop.
If you check out the Exclusive P3 this also has a motor/bearing/arm mounting system with a superior motor/bearing/arm platform that correctly references the arm to the bearing/platter. see
http://audio-database.com/PIONEER-EXCLUSIVE/player/p3a-e.html

The Denon's use a decoupled platter arrangement to keep motor energy way from the cartridge, but they do not address the lack of rigidity from the upside down design.

In my view any serious attempt to replinth theSP10mk3 would include throwing away the exoskeleton and motor covers and bolt the motor, bearing & tonearm mounting base rigidly to a common subchassis to maximise rigidity and minimise any potential movement within the platter/turntable/arm/cartridge loop.
I'm sure dropping the SP10mk3 into a slate or panzerholz "plinth" makes a difference but it is only a half pie solution in my view.
lewm
13,110 posts
 
All points well taken, altho thankfully all of the turntables you mention are more attractive than the metaphor you chose to describe them.
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