2. analog
  3. 128511-1637

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
toddverrone's avatar
toddverrone
840 posts
 
Ah, got it. Right now my rega rests on a wooden plinth that is resting on a partially inflated inner tube on my credenza. Getting rid of rubber would mean I need a new method of vertical seismic isolation for the plinth. Hence my spring inquiry..

Also, my tube pre amp is on a wooden plinth on an inner tube. So I'll need some springs there too..
toddverrone's avatar
toddverrone
840 posts
 
I thought I could just do the math and buy springs with the correct specs, but trying to find a source will be the hard part. Hence my inquiry.
toddverrone's avatar
toddverrone
840 posts
 
@slaw never mind. I read your earlier posts and saw you mentioned machina dynamica. I'll check them out
slaw's avatar
slaw
20,546 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.
More to discover