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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
russ69's avatar
russ69
3,501 posts
 

Something to try: Move your sub up between your speakers and turn it on its side facing forward. Just as an experiment. It might not energize your floor as much.

oldhvymec
5,101 posts
 

russ69 they work from 18-85hz there is NO rumble filter cut. The factory solution "in the manual" was to give the sub a 25 foot extension cable for phono. READ what they said. LOL  BTW it didn't come with the cable it was optional for phono use..

Regards

ct-ken OP
11 posts
 

Sweet sub with a ton of adjustment options, lucky guy. I did order a rumble filter that will hopefully be here next week. I think I can put that between the turntable and preamp only, but may experiment between preamp and power amp, not sure what would be best. I also ordered a minidsp 2x4HD so I can tweak my room, it’s something I’ve had in my mind for a while. Yep, mains are open baffle with long throw woofers, so not helping the situation, lol. 
 

Happy New Year to you as well! 

ct-ken OP
11 posts
 

Old Heavy,

Actually, the servo cord is not a standard audio cord, it’s a five pin cord with a connection as pictured below. The manual does not mention an extension as available. I think it’s a standard five pin DIN so I ordered a 25 footer from Monoprice. Assuming that works I can move the sub far across the room. The later Velodyne subs used a phone cable as you noted. That will get the sub out of the way. If the mains continue to wreak havoc, I’m counting on the rumble filter and modeling clay to correct the problem.

Thanks,

Ken

 

ghdprentice
6,965 posts
 

I don’t have any great insight into the nature of this problem. I find it curious. But my rule is never to put in filters or other symptomatic relief, there will always be unintended consequences. I would recommend working until finding the root cause and fix that. I might have had some problem very early on, but if so it is lost to my poor memory.

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