I am not sure I agree with all the discussion about what is and is not a good isolator, BUT in this case I think the problem is air-borne vibration, not mechanical from a shaky floor up through the stand and the shelf.
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.
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rotaries is absolutely correct; cones and spikes are not isolators, they are couplers---at least, in the very low frequencies needed for turntable isolation. The idea that cones and spikes provide wideband isolation seems to be a deeply-entrenched misconception amongst hi-fi fanatics, one that persists in spite of overwhelming proof to the contrary. Cones and spikes DO provide some isolation above around 10Hz, but below that frequency couple, not decouple, two physical bodies (such as a table and the shelf/platform it is sitting upon). The Newport and MinusK isolation tables are state-of-the-art (providing deep isolation to at least 2Hz), but rather expensive (over $2000). A cheaper, and admittedly less effective, method of achieving isolation is with a combination of lateral and vertical decouplers---roller bearings for the former, air springs (or metal ones) for the latter. A mid-priced solution is the Townshend Audio Seismic products, available as single pods, platforms, and speaker stands. Audiogon member Folkfreak employs the Townshend Seismic products in his excellent system. |
@miner42, you are not isolating anything with rigid materials like brass cones and spiked feet. Once you realize that most of that is useless BS, you can start to look at real isolation methods. Browse through some industrial catalogs and look at how isolation feet are designed and what materials they use. See how sensitive lab equipment is isolated. http://www.newport.com/c/vibration-isolators |
As lewm pointed out could very well be a room issue, If you walk around the room, even behind your speakers do you notice any exaggerated frequencies? Does the the issue arise even when not using the sub? Room treatments may be the solution or hold on to your hats adding another sub, as in "distributed bass" and room mode anomalies. |