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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
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..

ct-ken OP
11 posts
 

Based on recommendations here I ordered modeling clay from Amazon and will pack the open cavity in the plinth with it when it comes. I also moved the sub further away- about eight inches, lol. That’s as much as the servo control cable would let me move it, it’s not as long as I remembered. The sub is on a sheet of MDF and the MDF is on sorbothane feet, I suppose I could add an extra layer of each to try to further decouple. The sub crossover is set in the Velodyne controller at 85HZ and is not adjustable, unfortunately.  As for the Nobosounds, I had tried removing springs on the old rickety rack to no avail, it’s a good idea to repeat with the new rack to evaluate. Also, ordered a rumble filter. I appreciate the help here guys!

big_greg
6,570 posts
 

There is some talk of filling the underneith of the plinth with modeling clay to dampen the plinth.

Are you sure that you listed the correct model number for your turntable?  I searched on Google and couldn't find it.

If it is an older JVC model, the above "fix" may be very beneficial. 

I have a JVC QL-Y66F.  It's a beautiful table, but the plinth is super resonant.  I stuffed a few pounds of plasticlay inside and replaced the feet with feet from MNPCTECH.  When I first got it, it howled like a banshee.  After taking those two steps and also putting it on a Symposium Ultra platform I could play it as loud as I wanted with no issues other than a little woofer pumping at high volumes.  That was with a Rythmik dual 15" F25 sitting literally right next to it.

erik_squires
15,990 posts
 

Oh, sounds like the room may have been used as a meeting or conference space. Lucky duck!!

Then don't add bass traps without measurements. :) You may be OK, but the room may also be too dead.  If there's no diffusion you are going to get a very headphone like presentation.

ct-ken OP
11 posts
 

Eric,

Yep, it was used as an office by the previous owner of my home, so someone spent money I didn’t have to, lol. I do have a minidsp mic that I have yet to use, but have been boning up on YouTube videos to learn about it. The room may, in fact, be too dead but a measurement will help determine that. 

Slaw,

I just removed all but three springs in the nobosounds and that made a huge difference in volume ability before feedback! So, I’m definitely hearing an improvement, thanks for the suggestion! On the right track!

Greg,

Good catch on my typo in my original post, it’s a QL-5 or QL-50 depending on which designation you read on the table. I’m sure it’s an older unit, guessing nineties. I purchased all of the gear from my best friend’s estate after he passed and he was a big fan of 90’s gear.

 

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