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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
slaw's avatar
slaw
21,864 posts
 
toddverrone,

Once you figure out the weight of your Rega and wooden plinth, you'll have another decision to make, IMO.

The standard thought would be to go with 4 springs suited to the weight of your equipment. Here's another thought...what about three springs? Depending on the weight, 3 springs will give you a somewhat horizontal isolation effect in addition to the vertical because it won't be as stable as a 4 spring approach. Of coarse you can buy four and try each way. You won't be out much money. Food for thought?

Later, you can try cones under your wooden plinth as well/and/or some sort of discs under the springs. I use carbon fiber discs at some locations, dependent upon the final sound.  Lots of options.
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.
slaw's avatar
slaw
21,864 posts
 
There is also the issue of leveling...especially for a tt. You can find the "sweet spot" if you don't have a base structure that has the ability to adjust level.


slaw's avatar
slaw
21,864 posts
 
I use different sizes/weights of bags filled with lead shot to match the load when needed.
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.
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