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
@bdp24 ha, I had no idea. I have a teak cutting board on an inner tube.. 

Where did you get your roller bearings? I'd love to DIY, but I haven't found good cups.

Todd, I learned of roller bearings from audiophile recording engineer Barry Diament, a leading proponent of them (using them under every piece of his gear, even his Maggie MG 3.7’s!). He had his own "cups" machined locally years ago, and on his website blog details their design. Contributors on his site have offered their homemade versions of the isolators, usually of very low cost with a corresponding reduction in effectiveness (due to the softness of the bearing cups, often of plastic, wood, or cheap pot metal).

There have been a few professional/commercial companies making roller bearings over the years, most famously Symposium Acoustics with their Roller Block, it’s cups machined from aluminum. The Jr. model is the best deal, a trio of 1-7/8" double-cups with a half inch ball bearing between the upper and lower cup, priced at $180/set. The major difference between Diaments design and the Symposium Jr. is in the Jr’s use of top and bottom cups, in contrast to Diaments preference for a single cup, with the ball bearing itself in direct contact with the bottom of the component.

There is a small company in Canada making two versions of a roller bearing, Ingress Audio Engineering. Their Model 2 is identical to the Symposium Jr, just without the Jr’s black anodized finish, priced at $120 for a set of three double-cups with ball bearings. They also offer their Model 3, made to Diaments specs, a single 1-7/8" Alcoa 7075 aluminum cup with a very large 2" diameter "bowl" machined into it. The gentler slope of the bowl resulting from it’s larger size results in the bearing having a lower resonant frequency, therefore possessing greater isolation properties. The cups are also polished to a smoother finish than are the Model 2. The Model 3 sells for $175 for a set of three cups and ball bearings. The Ingress email is ingressaudio@gmail.com, phone number (519)981-2031.

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!

My main listening room is on the second floor, carpeted on a suspended subfloor.  I do not have the luxury of moving the sound system away from the speakers due purely to room size (15' x 15' x 8') and layout (open on two sides - second floor game/media room).  I feel my table is shielded from mechanical vibrations.  The VPI Aries 3D has the mini-HRX feet, this sits upon a 2.5" layered birch platform with a cork top which is on 4 isoblocks that sit on my marble-topped audio console.
My main listening room is on the second floor, carpeted on a suspended subfloor

Is the 1st floor,  the main house floor also suspended ?  Do both floors use horizontal wood beams?