FWIW ... I own a tricked-out Classic 1/2 plinth with a Classic 3 tonearm/base. I agree with everything Stan (Stringreen) said about checking the arm. My VTA, VTF and azimuth are pretty stable. I check every couple of months when bored. No changes.
I also agree with the advice about making sure the hex on the VTF counterweight screw is tight ... but not overly so. I also assume you're using the S-S counterintuitive gizmo. That's a big help.
Let's go back to the wires. In the past, I noticed that VTF and azimuth would change when measured at different places on the record if the tonearm wire that tied into the juntion box was over-twisted. IMO, less is more. I use a one donut as a bias weight on the anti-skating mechanism and err on the side of just a mild twist in the tonearm wire. If the wire is over twisted , the torque will affect azimuth and VTF a little.
Also, make sure there's clearance if you're using the AS mechanism. You may have to loosen the little AS ring that hooks onto the tone arm and move it around a bit as needed to ensure clearance with the VTA tower. My VTF and azimuth jumped around a bit until I properly set the AS ring.
Last point. VPI reconfigured the heavy azimuth stabilizing counterweight ring that attaches to the bottom of the heavy bell housing. The newer azimuth ring has larger counterbalance ears. That helped me a lot.
Hope this helps. You're not alone out there. To quote Mike, VPI service rep, if properly set up, the VPI/JMW arm combo sings. I agree.
I also agree with the advice about making sure the hex on the VTF counterweight screw is tight ... but not overly so. I also assume you're using the S-S counterintuitive gizmo. That's a big help.
Let's go back to the wires. In the past, I noticed that VTF and azimuth would change when measured at different places on the record if the tonearm wire that tied into the juntion box was over-twisted. IMO, less is more. I use a one donut as a bias weight on the anti-skating mechanism and err on the side of just a mild twist in the tonearm wire. If the wire is over twisted , the torque will affect azimuth and VTF a little.
Also, make sure there's clearance if you're using the AS mechanism. You may have to loosen the little AS ring that hooks onto the tone arm and move it around a bit as needed to ensure clearance with the VTA tower. My VTF and azimuth jumped around a bit until I properly set the AS ring.
Last point. VPI reconfigured the heavy azimuth stabilizing counterweight ring that attaches to the bottom of the heavy bell housing. The newer azimuth ring has larger counterbalance ears. That helped me a lot.
Hope this helps. You're not alone out there. To quote Mike, VPI service rep, if properly set up, the VPI/JMW arm combo sings. I agree.