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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
rotarius
431 posts
 
My tonearm is only 32" away from my speaker but slightly behind the baffle. There is no issue with feedback at all.  Airborne seems unlikely from my experience. 
totem395
390 posts
 
lewm
"Start with implementing room treatments rather than
applying this or that band-aid." Isn't there an internal contradiction in that sentence? Some would classify room treatments as a bandaid.

I guess it all comes down to the proverbial "chicken and the egg"

If a room has particular issues ie modes that propagate and are not dealt with any amelioration down the chain is in my mind the "band-aid".
In a studio or other professional venue the first thing that's considered is the room, since that will always be the limiting factor for whatever follows.

Is the room in the OP's case the problem? The way to confirm is to run a sweep and determine where and why the anomalies are present.

Personally the whole room treatment subject is one of the most 
overlooked and discounted topics considering its effect on whatever 
gear, tweaks or changes follow. Thats my take on it.






bdp24's avatar
bdp24
10,080 posts
 
Todd, the Townshend Seismic Platform (the "original" Seismic product, which I have and use, not the current "spring-in-a-bellows" Seismic Pod design) actually IS a slightly inflated inner tube inside a metal frame. The top and bottom damped metal platforms are separated by the inner tube, and it provides, as you say, a lot of vertical isolation. I then have roller bearings on top the platform for the lateral isolation they provide. The combination works real well.
toddverrone's avatar
toddverrone
840 posts
 
@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.
bdp24's avatar
bdp24
10,080 posts
 

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.

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