VPI Prime Sig/Lyra Delos / Feedback ...help!

Ralph@atmasphere or someone technical needs to chime on  this one.

Curious to read their take.

I have heard a number of uni-pivot arms, including two that I owned (Graham 2.2t and Basis Vector 3) and none of them suffered from any feedback issues.  These arms were used with Lyra Helikon and Titan cartridges.  If there is a feedback issue (resonance) it is either a very unfortunate combination of all of the mechanical parts of your system--the cartridge, arm, table, table support--or, a defective cartridge.  

What you are calling feedback when playing loud passages might be mis-tracking.  That mis-tracking can be a product of incorrect alignment/setup or, again, a defective cartridge.  

It is almost assuredly not an issue of incompatibility with your phono stage.  The only kind of incompatibility that would remotely sound like feedback would be an overload (too strong a signal being fed into the phono stage), but, that is not the case because you heard the same problem with different gain settings.  

My "bet" would be mis-tracking caused by a defective cartridge.

Yeah, I've fought with that on VPI tables in my "difficult room" office setup. Went though all the usual "maybe it's the cartridge / phono / etc" and tried several combinations of each. I've even used 2 different VPI tables here: Aries 3, Avenger Ref. These VPI tables and their arms do seem to pick up frequencies around 100 Hz plus/minus. The Clearaudio Innovation Compact I used prior to these didn't have any problem in these frequency ranges, but then was a nightmare in the subsonic frequencies - which are potentially dangerous to your speakers. 

If your rack / shelf / feet aren't isolating enough at these frequencies, you'll have a problem. Feet can help a little - the HW40 feet seem to mitigate it by ~ 6dB? The classic Signature feet were absolutely useless. The shelf you have the table on matters a lot. I have a Critical Mass Platinum on a Sotto Voce (very expensive) that's surprisingly ineffective at these frequencies - in fact I think it's contributing to the problem (I place more blame on the rack structure underneath). I've heard from a friend that Symposium Ultra platforms was effective for him. I think a Townshend Seismic platform would probably clean it all up, but they're awkward to use and I sold mine with the Clearaudio. 

The one really surprising finding I've made in all this - the VPI arms with 3D material pick up this feedback a LOT more readily than the older metal arms. Even unipivot vs. gimbal vs dual vs fatboy (they're all 3D material) doesn't affect thing like the actual arm material. The metal wands are simply much quieter in this frequency range! The worst wand I had was an older 3D 10" wand (shiny finish). If you have an arm+cart combo that's quieter, it's probably due to the wand, not the cart. 

One last weird finding - I noticed that even the SUT I choose, and its placement on rack, can have a big impact on feedback. I don't know if that's due to the SUT itself being microphonic, or feedback back into the arm through the cable. The Bob's Devices Sky (lightweight little boxes) gave me the worst feedback problems when positioned on top shelf next to my table, until I moved it to a lower shelf - the it quieted down. The EAR SUT (much more substantial box) has no problems on the top shelf. 

@tablejockey @mulveling @larryi @atmasphere 

so frustrating....thanks for the help ..I wanted to add that the low end rumble is basically like the bottom end is not tight & consistently ringing...even tested with acoustic guitars (no drums) still get the low end rumble..

So the latest is the arm was sent back to VPI for repair of the white lead...when it returns I'm going to try some better isolation ...incidentally my room is heavily treated with sound panels ,bass traps, sound absorbing curtains....

I might try the HW40 feet I have , they seem way shorter than the Prime Sig feet so not sure all will line up with motor? 

I might try the HW40 feet I have , they seem way shorter than the Prime Sig feet so not sure all will line up with motor?

@tommypenngotti Yep I had to shim it with hockey pucks as needed to line everything up. The HW40 feet will help for sure - it’s worth it rearranging for.

The issue as you describe it is extremely similar to what I’ve fought with. In fact with some of my worst configurations, it could get excited to an almost runaway level of that rumbly / hum noise (grows in level on its own, until I mute). And yeah, acoustic treatments won’t do a damn thing about it, either. Best I can tell, the problem is due wholly to structure borne energy, not acoustic.

The top shelf and its support underneath is what determines how much of this energy your table has to deal with. The VPI arms are sympathizing with the energy (less for the metal wands), and the table plinths don’t do much at all to stop it. Squishy feet like HW40 are really your last line of defense. Think if I had a rack with cross-bar support level (at least for the top shelf), and support discs positioned more toward the interior of top shelf, that would help a LOT (e.g. higher-end Critical Mass, or for a LOT less money Adona Reference racks, etc). As it stands, my Sotto Voce rack only supports its top shelf along the very front and back edges (with a few simple rubber bump feet) which I think is a big part of the problem in my case - the CMS Platinum shelf, substantial as it is, acts like a drum skin at the problem frequencies.

Here’s how I "test" a given configuration: lower the stylus in a still groove (turntable at rest!) and turn the system on / un-mute at your normal listening level. Modestly thump the top shelf near your table with a few fingers. That "drum" like feedback level tells you how bad that config is. The worse ones will be much louder per thump, with a very long-lasting ringing effect. Get a feel for what it is now so when you change configs you can meter it against that. An iPhone can record these frequencies just fine, so take videos for comparisons. However, you will need to playback with decent headphones to reproduce those frequencies.

The problem (obviously) gets exponentially worse at higher SPLs. Guys who cap out at 70 - 85 dB are going to be like like "huh? my table is dead quiet!" because they won’t ever hit that threshold to excite these resonances. I listen loud (up to mid 90 dBs continuous), and yeah in this small room with bouncy floors it’s a struggle. My main rig is in a bigger room with much more solid floors, and it was easier (also that table is on a CMS Maxxum which is much better).

Which exact VPI arms do you have, and which is the one that’s been the bigger problem? The metal arms are just much quieter at these frequencies, in my experience. Sure they might "ring" at high frequencies, but that is MUCH lower in level and easier to deal with.