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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

Showing 2 responses by millercarbon

millercarbon's avatar
millercarbon
12,531 posts
 

Just a guess, but I'm thinking you should use only 3 springs per corner for that turntable- and maybe only 2! I see all 7 in the picture, so even after taking some out you probably need to remove another 1 or 2.

The Nobsound should be compressed to only about 1/4" space, and the turntable bounce very slowly when adjusted right.

Then take the removed springs and use them under the sub. Use a 1/4" drill bit to make divots for the springs like the Nobsound feet. Use wood, MDF, anything to hold the springs. You will probably have enough but if not order another set because isolation is the solution to your problem and the sorbothane just ain't cutting it.

Ultimately your best will be Pods, a lot better than Nobsound, and Podiums under the speakers. This won't just eliminate the rumble it'll greatly improve all aspects, like a new system.

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.

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