Best tonerarm match for Acutex M320 III STR cartridge

Dan
You may find the MyMat helps, not sure as never had a feedback issue.
I assume at just 1mm thick you will be placing this on top of the copper plate.

Curious as to the statement  " sounds spectacular until feedback sets in"

Is it at a certain frequency or pitch that it starts or purely volume level dependant?

I love the Acutex 320STR III, and I have used it on my Dynavector DV505 and (believe it or not) on my Fidelity Research FR64S, where it really should not work because of the high compliance/high effective mass mismatch. I did use a lightweight (8 gram) headshell on the FR. The DV505 and 501 would have very low effective mass in the vertical plane and high effective mass in the horizontal plane. That is the deliberate intent of the design. There is no reason your Acutex should not work well on the DV501. I would suggest you look elsewhere to solve your problem, but buying a new tonearm is always an adventure, if that’s what you’re after.
Sorry, I did not see the above post where you say you would prefer not to replace the DV501. I agree.  Can you say in more detail what you hear that you call "feedback"?

Uberwaltz, Lewm,

The feedback is volume dependent. It happens when I turn up the gain to where it's how I like to hear it, below the clipping point on some of my lower powered amps. And, as I mentioned, it sounds spectacularly good until the feedback begins. The signal has a "fluttery" sound, or like a vibrato.

Lew, I looked at your Lenco, is that a slate plinth it's in? Thinking about this, I've had this cartridge for years, and I don't remember having this issue before. The only thing that's different is a change in line stages, I went from a kit built Transcendent Sounds Grounded Grid to a Modwright SWL 9.0 Line Stage, which is much more musical, but I don't know how that would cause this feedback issue, although it does seem to have quite a bit more gain. 

I hope get a handle on this, the M320 III STR is my favorite cartridge now, I kind of miss its use.

Regards,
Dan 

Dan
A lot more gain could certainly contribute.
Do you know what gain?
I run 44db gain most of the time on my Nova 3 although not had the acutex mounted for a while and not with the Nova. Last time I used it was with a Chinook at 40db gain.
The 320str has over 3mv output so really should not need any more than 40db gain IMHO.
Is it possible to reduce the gain at the Phonostage?
Yes you would then need more preamp volume to bring you back to the volume level you decide but if it is Phonostage gain related you may have your answer.

Uberwaltz, I have not changed phono stages, just the line stage. In any case, the MM gain is 50db, and MC gain is 66db.The gain provided by the line stage is 15db.

I've been using the same Modwright SWP 9.0 SE Phono Stage for around six or seven years now, this seems to be a new issue I don't remember encountering before. I remounted the Acutex again today, I'll try and sleuth out the problem some more. I'll get back to 'ya.

Thanks, and Happy New Year,
Dan