How to isolate turntable from footstep shake or vibration

@lewm , as far as F22 avionics are concerned I doubt the government would publish such information. For certain as you suggest the "brain" is oriented to gravity and it knows it's altitude and ground speed. It also knows how to fly the plane. There is no way you can protect the brain from the wild forces applied to it during aggressive maneuvering. The plane is capable of pulling at least 6 G's in any direction, more than any human could stand without a flight suit that supplies counter pressure. That would pull the wings off a 737. This is a lot more force than any coincidental vibration and there is no way to protect the electronics from this. They are just built to take it. I seriously doubt there is any "micro instability" Would you strap yourself into a Mach 2 fighter plane that relied on micro unstable electronics? I wonder what "micro instability" of 20,000 pound thrust vectoring would do?

You would think just looking at a tube with it's delicate appearing insides that it would be sensitive to vibration. Is this reality or lay instinct? I use a tube phono stage which uses 6922's. It is not the tiniest bit sensitive to vibration, at least as far as I can hear and I have done some pretty crazy things. I have 25 foot long RCA interconnects from my Krell amplifier days so we put my turntable and phono stage on top of a subwoofer just for fun and to prove that the Sota was impervious to vibration. I had no intension of testing the phono stage. But, tonearm interconnects are only so long so the phono stage went with the turntable.

@mijostyn  In case you are still looking for proof, please take my comments here as such that can be demonstrated **very** easily. What your test above didn't take into account was how much vibration was actually getting from the sub into your phono stage. At any rate its unimportant; the word 'microphonics' exists for a reason; it refers to a sound that an active device like a tube can make when its vibrated. For this reason Ampex iso-merically mounted the circuit boards in their famed 351 vacuum-tube tape electronics, just as we do. So as a tube equipment manufacturer I can tell you that not only are **all** low signal level electronics (like a phono section or line stage) affected by vibration, but when you take steps to prevent it, the electronics will perform better. This is both audible and measurable. And yes, I'm including solid state electronics here- if you think they are immune, you are incorrect, although they are certainly less susceptible than tube electronics. But that is different from immune.

Damping materials, anti-vibration platforms and stands will all help low signal electronics in this regard.

a tube phono stage is not a fly by wire computer, or 4 of them. 

While you might not find all that much about the particulars of the F-22 avionics detail design, you can learn a bit by looking for details on MIL specs for things like conformal coatings, potting, circuit boards damage, damage tolerance. ….

Some of us, who have built, tested and supported advanced systems will have a deep understanding of vibrational impact on both structures, analog and digital..including effects of EMP…

( in a time long ago, i had something to do with the F-22…. just a bit part…Let’s call it a third…. )

Aesthetix and Vandersteen both employ HRS products in or below products  for good reasons.

enjoy the music.

Shock/vibration isolation of avionics is documented and easily accessed - examples  Microsoft Word - avioinics_iso_revC.doc (vibrationdata.com), and compressed_PC6116_AerospaceandDefenseIsolatorCatalog.pdf (lord.com).  Exactly what shock & vibration performance the avionics has to survive can be classified.

@atmasphere,

in my prior post I should have gone into greater detail, but for the OP, when the floor bounced in the upward direction, the turntable spring went into compression.  But because the spring was not stiff enough the spring fully compressed at which point the 'suspension' essentially bottoms-out and now there is no suspension and the force is transmitted directly to the table. 

In your circumstance, I suspect that the floor is resilient/soft enough that foot fall causes a ripple effect which then has vertical force component and a horizontal force component.   Use of ball bearings to absorb horizontal vibration is well documented; ergo, they worked for you. These vibration reducers originally were developed for audio use - Vistek - Designing with Series 320 Vibration Isolation Bearings (newport.com).

Mijo, Mijo, Mijo. You consistently mistake your own observations and opinions for science and facts. Tubes are microphonic, some more than others, and most tube gear does benefit from isolation and dampening. Not necessarily with spring suspension. Like I said, some guys even isolate, suspend, or dampen their solid-state gear, although the rationale for that is perhaps less obvious. If you ever looked inside a Halcro preamplifier, for one example, you would see that the entire printed circuit board has been sprayed with a rubbery coating to dampen vibration of the individual components. And that is solid state to the utmost.