@richardbrand Thank you for responding. (I chuckled at your reply to Elliott Necomb above.) Yes, it certainly seems your electrical diagnosis is correct. The same thought has occurred to me. I’m going to have to remove The Vessel cartridge to verify, but I believe the top of the cartridge is plastic. The stylus insert’s exterior is plastic. The only metal part is under the black plastic on top and behind the red stylus plastic in front. The cartridge mounts with bolts and nuts, so there is no metal-to-metal contact at that point.
So . . . I’m wondering if the metal portion is acting more as a shield than as a conductor; and that, as a shield, it needs a connection to ground. I would need to provide that connection, at least to the cartridge.
The tonearm has a 5th black wire that provides the ground into the tube. That is to say, the wire is connected to ground at the same terminus as the grounding wire on the interconnect— the wire that runs back to the screw on the case of the phono stage. [Edit: The switch may interpose here, bringing 100 Ohm lift in and out of circuit, not sure, need to check, see more below.] At the ELAC phono stage I can choose betwen either a screw labeled ‘signal’ and one labeled ‘chassis’. The other end of the black wire , as I said, disappears into the rear of the arm tube at the bearing end and does not appear at the connector at the cartridge end of the tube. My Ohm meter tells me the connection from the wire in the plinth to the front portion of the tube is good. I don’t think the front portion of the tube is electrically connected to the tonearm tower or bearing, see below.
The shielding of the tonearm wires inside the plinth (if the term applies) is interesting. A short length (2-3”) of bare ‘woven’ shielding (the kind that resembles so-called Chinese handcuffs, in which tugging at the ends shrinks the cross-section, in the ‘handcuffs’ tightening down on each finger inserted into the ends) which is soldered to the same ground wire potential as the aforementioned ‘black wire’ above, and, at the other end, is secured to the tonearm tower. This coonection scheme, in my opinion allows the ‘shield’ to serve as both a shield and a conductor. Somewhere in there (I would have to open it up again), there is a 100 Ohm resistor that ‘lifts’ the signal ground from the chassis ground.
I think I might need to investigate this aspect of the grounding. The purpose of the switch I added on my first go-round with this turntable was to allow me to switch from chassis to signal ground at the turntable and give myself the same choice at the turntable as I had at the phono stage.
Finally, you are right about some cartridges using one of the pins for grounding. The ‘ground strap’ for the left channel (-) signal (blue wire) on the Stanton cartridge is exposed and labeled ‘GND’. The same (necessary) connection may be required by The Vessel, but the connection is hidden within the body. I guess I could break out my Ohm meter to investigate.
