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Turntable Rumble/Feedback

Hi All,

I have the following set-up:

Nakamichi Pre-amp

Krell FPB 600

Velodyne ULD-15 Sub

JVC PL-50 Turntable with Grace tone arm and Audio Technica Cartridge

Carver Amazing Speakers

I have been trying to unsuccessfully eliminate a low frequency audible feedback when attempting to play vinyl. If I turn the sub off completely I can play a record, but really no bottom end. The Velodyne servo control has a low pass filter that I think cuts at 85 hz before getting to the Krell. With the sub on, I can play very low volume. Turning the volume up causes an audible rumble that gets louder in a feedback loop.

I originally had the table on top of a rickety old component rack and figured that was a large contributor. I had racket balls cut in half under two layers of MDF and also a set of springs under the table feet to no avail.

I received a Pangea Vulcan rack for Christmas and filled the tubes with layers of wax, sand and wax to try to add damping and assembled it tightly. Just took it for a test spin and same result. I previously had a set of Vandersteen’s hooked up which behaved the same way in terms of feedback.

The sub is sitting on a layer of MDF that has Sorbothane feet under it. The rack and Carvers are sitting on a hardwood floor. The sub is only about five feet from the rack.

So, I’m looking for advice on how to eliminate this rumble/feedback. I read in another post about using a KAB RF-1 filter, but not sure it will work as appears the application is for woofer pumping subsonic. Was also thinking about a mat below the turntable, but not sure if that will help as if I tap on the Pangea shelf I am not hearing it through the speakers.

As a final note, the problem occurs not only when playing vinyl but also if the turntable is off and the needle is fist sitting in the groove, so should not be motor noise. Thanks in advance for any advice here!

Ken

 

ct-ken
Post removed 
slaw's avatar
slaw
21,043 posts
 

Have you experimented with removing some of the springs in the Nobsounds? They will be more effective when around halfway compressed. 

I agree that you could use some bass corner traps.

millercarbon's avatar
millercarbon
12,531 posts
 

I had almost this exact same thing, only my rack is a lot more massive so mine wasn't as severe. But same exact thing. Right down to Nobsound under the turntable. 

Problem is different things isolate at different frequencies, and Nobsound are not effective enough at this frequency. Replaced them with Townshend Pods, and that was the end of that.

You might be able to get away with moving the Nobsound to under a sub and using Pods under the turntable. But as severe a problem as yours might well call for the Full Monty of speakers on Podiums, subs on Pods, and turntable on Pods.

I would try slaw suggestion first, remove some springs it looks like your Nobsound could be compressed more. This will shift the resonant frequency lower, possibly low enough to suffice. So try it. But don't get your hopes up. Mine were optimized, still no luck. Nobsound are great for the money, but just not in the same league as Pods and this is one of those areas that highlights the difference.

aberyclark
1,355 posts
 

Looking at the pic, to me it just looks like a whole lot of vibration going on in a confined space. Is the hardwood floor on concrete or is there a basement, crawl space underneath? I know it would be a pain, a rug or runner underneath your rack and sub could not hurt. Double check your sub crossover to make sure its as low as possible for your speakers. You have some big ol' speakers and subs moving a lot of air in that space. Keep curtains closed. What would happen if you moved your rack to in between the main speakers? 

oldhvymec
5,101 posts
 

I can’t get over how close that type of sub is, to the rack and it’s NOT decoupled. It’s on a mat? That won’t work. That type of sub rattles the heck out of the floor plane, the one that is CLOSE to your TT. Bla, Bla, Bla everyone, that won’t work, I don’t care how it sounds, "it sounds best there", that does not mean it sounds good at all. There is ZERO dampening in that set up. Everything is going to vibrate. It’s not hard to SEE if you just look. No carpet, traps, drapes, and then pack a sub right next to the rack..

There I said it.. Sorry if I hurt anyone feeling.. LOL Like I give a crap.. Ground up, not paint first.. It’s like talking about 600 horsepower engine in a car with a flat tire and a broken windshield. Fix the flat and the glass, first.. Mercy.

Happy new year..

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