Turntable Rumble/Feedback

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.

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.

I had same issue. Thank you for the suggestions.

IMO, it’s never a great idea to put springs or any other flexible foot under a speaker, particularly a subwoofer.

Ooof, I struggled with this on a couple VPI setups in a "tricky" room / floor scenario. The feedback sound can range from an audible rumble to very much like a ground hum (but not one). Definitely NOT the motor. It only emerges during high volume levels (and increases with it), and it can possibly hit a "runaway" threshold.

Best I can surmise, it’s the plinth and arm (or particular materials & design) which are energized by these frequencies. Interestingly, the metal VPI unipivots had significantly less feedback than 3D wands or Fatboys. Most footers (rubbers, polymers, hard cones, etc) had almost no effect. VPI’s HW40 footers with the really squishy / compliant foam layers had some positive effect, but didn’t fully solve the issue.

Clearaudio’s Innovation with the magnetic bearing didn’t have humble / hum feedback issues, but had the woofer flapping (subsonics) PLENTY bad (which the KAB filter does solve) - haha, what a torture test for tables here in my office rig!

I’m surprised your attempt at springs didn’t solve it? But they must have been the wrong springs / wrong loading or tuning. That’s the magic of SOTA’s internal suspension - in the same room & setup, NOTHING gets past my SOTA Cosmos. No problems at any level of playback. Of course, I don’t run a sub and that will pump plenty of bass back into the system. And you still need to ensure you don’t excite the suspension during playback (rigid rack mounting - you’d be surprised how easily most racks can sway enough to matter).

I think a Townshend platform or pods with the right load rating would solve your problem, but they’re a bit spendy - but then they’ll be way better here than some of the much more expensive "constrained layer damping" audiophile platforms. Which are generally pretty useless for "macro" scale problems like this.