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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
 

You see that rumble filter on the plate? Rythmiks plates offer a few more options, I guess. I'm using GRs but they use Rythmik plates. Darn near bullet proof. Very versatile. I do like the finish on that sub you have though. The rumble need to be on the mains, not the sub. Still makes me wonder without one on a servo and the software doesn't understand "rumble" that could be a problem. GR took vinyl into account.

Your mains are open baffle woofers, right? They usually have a bump @ 40hz and down, I didn't even think of that.. That type of speaker is going to be more prone to pumping. Trying to dig decent bass out of the system might be a little tricky with vinyl. In non servo bass heavy systems, I've got a few, I just CUT 40 hz down. Most of the vinyl especially pre 70s the bass is cut pretty high anyways. All the 78 are cut higher than that.. It's just not on the media.

The actual mechanical "Rumble" on my new Thoren is so low they don't even publish it. But it will sure act up without a lot of work or very little work and a rumble filter.. LOL

Happy New Year

oldhvymec
5,101 posts
 

3) Cable kit with 25' phono cable for connection from controller to woofer cabinet, and a 3' patch cord for connecting the controller to your pre-amp. Speaker wire is not included.

<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<>>>>>>>>>>>>>>>>>>>>>>>>>>>>

This is from your manual. It couldn't be clearer what the longer cable was for. There is NO rumble filter consideration with this old servo unit.. WAY ahead of its time, but a guy that tried to fix one moved on the Rythmik, it was funny at the end of the article 3 or 4 months later. 

Progress March 2015

The amplifier and speaker have moved on to the next owner. They were replaced by a Rythmik Audio subwoofer.

I cracked up.. Sure take care of your stuff though.. Hats off for sure..

Regards

russ69's avatar
russ69
3,520 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! 

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