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Feedback through turntable

My system consists of a McIntosh C2300 preamp, MC452 amp, MCD500 SACD player, VPI Aries 3D with Ortofon Cadenza MC cartridge, Manley ChinookSE phono stage, PS Audio P5, Sonus faber Cremona Auditor M speakers and REL B1 Sub bass system.  My issue is with turntable use only; SACD has no issues.  On my pre when volume is +55 (peak at 45watts) I start to get feedback through the turntable - a sort of low freq sound, back off volume and it goes away.  My Auditor M speaker is about 3 ft away and in front of turntable.  I do have a rumble filter (KAB) installed between preamp and phonostage to help with sub woofer pumping.  Due to room layout I cannot rearrange the setup/move turntable.  My turntable is on a 2.5" block of wood and that sits on 4 isolation blocks via spiked feet.  Any thoughts how I can eliminate this problem?  Harry Weisfeld with VPI states he has 4 15" woofers (JBL Everest) near his Prime Signature setup with no issues at all.  Why am I having this problem and how can I eliminate it?  Thank you in advance for all feedback.
miner42

Showing 7 responses by geoffkait

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geoffkait
23,365 posts
 


stringreen
Marble is awful for a VPI.....it rings like a bell. DO try Bearpaws as I mentioned above. Roller bearings are no good for VPI...it must be anchored to the center of the Earth. Anything that allows motion doesn’t work. ..springs, Gingko balls, etc.

I have isolated many VPI turntables on my spring systems, including the new very heavy VPI Flagship turntable (on my new Super Stiff Springs), with great success. By the way, marble as the base under the component on a spring based iso system doesn’t ring. Anyone care to guess why not? The earth is not a stable platform, it is a springy one.
geoffkait's avatar
geoffkait
23,365 posts
 
Todd, post this over on the tiny bowl thread and I'll consider answering.

cheers,

Geoff Kait
Machina Dynamica 

geoffkait's avatar
geoffkait
23,365 posts
 
"So far I like the sound of the butcher block on springs better than on the inner tube. As far as leveling/ mass loading, my butcher block is 2" thick and plenty heavy, especially when the tt is on it. When I drilled the holes for the springs, i made sure they were as equal in đepth as possible. That, combined with the self leveling nature of springs has made leveling a non issue. I also thought of using three springs, but it was too wobbly when I tested it."

sadly the geometry of inner tubes and air bladders is all wrong. The contact surface area is much too large and the rubber material damps too much, compared to springs.

geoffkait's avatar
geoffkait
23,365 posts
 
Springs are self leveling. Absolute level is obtained by slightly moving one or more spring using thumb and forefinger. Obviously the load should be distributed uniformly when level is an issue. Tip: for CD players absolute level of the spinning disc is usually not the same as the level of the top of the chassis.

Addendum: I actually like brass just slightly more than I like lead, which I loathe. They both seem like such a good idea, too. Glad to hear you're are able to live with them. 😃
geoffkait's avatar
geoffkait
23,365 posts
 
I’m not crazy about lead. It's a non audiophile-friendly material. Messes up the bass. Don’t take lead for granite. It resonates throughout the system. Try substituting a different material just for grins and I think you’ll see what I mean.
geoffkait's avatar
geoffkait
23,365 posts
 
Going from 4 springs to 3 springs won’t buy you much. Neither 4 springs nor 3 springs provide much, if any, horizontal isolation since springs are inherently stiff in the lateral direction. There is some isolation in two rotational directions IF the springs are actually matched to the load and the ISO SYSTEM is not too stiff. The ISO SYSTEM resonant frequency will be lower for lower number of springs.

All things being equal I usually recommend preloading the springs with mass such as granite or marble, if needed for matching the (relatively light) load to the spring rate of the springs.
geoffkait's avatar
geoffkait
23,365 posts
 
Just to mention the roller bearing assemblies actually provide very good isolation in not only the horizontal plane (all horizontal directions) but also the three rotational directions - twist, roll and rock, as a consequence of the shallow cup and bearing motion when forced, which are also important since the seismic vibration produced by Earth crust motion, traffic, etc. arrives at the house or building in the form of waves, like waves on the ocean passing under a boat. My first product, the Nimbus Sub Hertz Platform, isolated in all six directions and had a resonant frequency as low as 0.5 Hz!

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