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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
billwojo
397 posts
 

JVC didn't rebrand other tables. They were a top engineering company that designed their own tables and built some high end TT gear that is very desirable even today. They also designed and built some world class tonearms along with supplying motors and drive electronics to Micro Seiki.

For some reason most of the JVC tables shipped to the US had light weight plinths, they can be prone to feed back. In Japan, a lot of the upper tier JVC tables used constrained layer plinths, very massive and heavy. My guess is it added a lot to the cost to ship the better tables over here.

 

BillWojo

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.

4krowme's avatar
4krowme
542 posts
 

oldhvymec,

 

  Yah, I agree with the cartridge being a transducer, like a mic. 

 There was a moving iron cart that I had recently that caused a hum problem just due to the fact MI carts are more prone to being affected by AC fields. They also can lose their strength over time, which means that you will be turning up the volume and noise is higher because of it (at least with the phono pre I had at the time). 

  So some here are thinking about the TT itself having an issue, and others say cart. There were other thoughts as well, and I hope each can be eliminated or somehow realized that there may be a combination of devils. This is a good thread to follow. It is bound to lead somewhere should the OP pursue it.

bicyclejoenyc's avatar
bicyclejoenyc
5 posts
 


BIG_GREG "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." 

Thanks Greg , I've had the JVC QLY-66F since 1982 when I bought it new. It seems to rumble more as it gets closer to the spindle, I was hoping I could adjust the tracking angle to raise the bottom of the Clearaudio Maestro V1 body a wee bit.
Think it may be too close. My table is sitting on a slate bar about 3 feet from my JBL 240Ti, but the angle of the drivers is not facing that table
I am going to take a look for the feet you recommended. And clay I've enquired about getting a new plinth  but seems the layout is too difficult to adapt according  to the custom shop I contacted so clay it is. thanks for the tips.

 

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