Apocalypse Now?—Technics sp10 problem s

Banquo, This is way out on the end of arguing the number of angels that can dance on the head of a pin, but suppose in your thought experiment that either the turntable or the tonearm pod is subjected to a vibration or resonance that is not simultaneously experienced by the other. There is NO such thing as perfect isolation. For example, the pod has to sit on some surface, probably the same surface that is also supporting the tt but in a geographically different place. The shelf itself is going to be subject to resonances that create standing waves with peaks and stationery nodes. Suppose the pod is sitting on a node and the chassis is sitting on a peak? Voila', the chassis moves, albeit at a micro level, while the arm pod does not. If the pod is coupled to the chassis, ideally not in contact with the surface of the shelf, then they both move identically in response to a standing wave of mechanical energy passing thru the shelf.

If you got an SP10 Mk2 and tonearm for less than $800, then you got a steal. I suppose the drill hole in the chassis played a role in that low price. But there is plenty of room there for you to spend some bucks on the electronics and still be within market value, not to mention you will know you are listening to the SP10 the way it ought to be heard.

Banquo, you must accept that every material is subject to vibration, it is just a question of the resonant frequency for each one. I'm not a physicist so admit I am not the best person to answer your question. But my understanding is the higher the density of a material (in general) the lower the resonance. This is why some favor high density in plinths -- to lower the resonance point below the critical 8-12 Hz range. (Which could explain why some prefer plinth less designs, if the lack of low frequency damping and a "brighter" sound better suits their systems.)

I believe this translates to tone arm mounting as well. With a secure mechanical coupling between arm and spindle/platter, material frequency differences (example aluminum and brass or acrylic) may be damped. If each stands alone, they do not damp one another, they can move independently. A further point; many do not realize the potential for urban living environmental activity. I live by a busy street. My turntable is mounted on a wall shelf for isolation. But I can put a stethoscope on the braced plywood shelf and hear traffic going by. If you have an amplifier on the same shelf as your turntable you could experience the same thing. In that environment I would not want my tonearm to be subject to micro-vibrations picked up and translated by a base that was not mechanically damped (attached) to the spindle/platter. Again, consider the extremely small movements of the stylus tip to generate signal.

I think your question on isolating the arm from table motor vibrations has two answers. A decent design will minimize motor vibrations to begin with. But if the motor is noisy, there could be an energy path from the motor, down through the shelf, then up through the freestanding arm. By the time the energy reaches the arm and then stylus, the various materials it traveled through will change its frequency, thus it will vibrate differently than the platter and record. When the arm/cartridge and spindle/platter are mechanically coupled, I believe they should at least vibrate in unison, thus minimizing the impact on the stylus in the groove.

I hope this makes some sense and perhaps another person with more technical knowledge can correct or fill in these points.

Banquo - I agree with Lewn that it is worth fixing up the sp10. I believe it will only go up in value.

Regarding this thread - you could link it to Halcro's. I will post further impressions of my set up there.

Here is the email from the designer of the ET arm I am using - Bruce Thigpen.

Chris,

The installation method looks good. It is very important that the tonearm cannot move with respect to the platter, in other words they should be coupled together. It looks like your installation meets that requirement, thanks for the photographs.

brucet

...not to mention you will know you are listening to the SP10 the way it ought to be heard.

There is a lot to be said for that. Now all I have to do is get my wife to share this perspective. She was already rolling her eyes at my bringing it to Mirko when the TT, in her words, sounded perfectly fine. Of course, she is right that it did sound perfectly fine--except when it didn't.

This is way out on the end of arguing the number of angels that can dance on the head of a pin...

I'm a philosopher by training, Lewm, so I rather like this type of argumentation :).

But I can put a stethoscope on the braced plywood shelf and hear traffic going by.

Really? Wow. Glad I don't live in NYC anymore. That's the first time I've ever said that.

Thanks, gentlemen, for offering a better picture of what's at stake.

Ct0517: but your set up is NOT coupled in the sense that Lewm and Pryso are talking about, right? If it is, then I'm really confused.

You don't need to live in NYC. The earth seems to shake easily here in California. ;^)