A question about tone controls ground connections...

[archaos]

...and DC-coupled cathode follower. BTW, perhaps the answer seats in the title (?)

Hi guys, I'm somewhat stuck with my new project : I know that the grounded pin of a volume pot, for instance, if it is located at the grid of the second tube section, should go to the local common point for that second tube section's cathode resistor and bypass cap.
Yet, how about tone controls located between cathode follower & PI (AC-coupled long tailed pair) ? Does the ground connection ought to be made at the follower's cathode load resistor, Rk2, or at Rt/Cg2 ground junction ?

To my eyes, it should be the former solution, since Rk2 is closer to the tone stack in the circuit, but I'm uncertain...

Any suggestions/help highly appreciated. 

[HotBluePlates]

The tone circuit is between the output of one circuit (the cathode follower) and the input of another circuit (maybe a phase inverter input in your amp?). The ground for either of those circuits probably works just as well.

If there is a large physical distance between these points, go with the one that is physically closer.

[archaos]

The tone circuit is between the output of one circuit (the cathode follower) and the input of another circuit (maybe a phase inverter input in your amp?).

That's it.

go with the one that is physically closer

Thanks for the tip. ;-)

[tubeswell]

I ground any component part at the same ground return point as the filer capacitor from which that part is taking its power supply - following the system described in this article http://valvewizard2.webs.com/Grounding.pdf for the reasons therein. So provided that the ground return for the volume point is going to the same ground return as the filter cap from which the previous stage* is drawing its power supply, it'll probably be okay. (If the next stage comes from the same power supply node, then it probably won't make any difference)

* on the assumption that the pot forms part of the AC load for the previous stage, and the role of micro-wobble in the ground return at contributing to unwanted hum is likely to be more significant as part of the output impedance from the previous stage, than it is as part of the input impedance of the following stage (I stand to be corrected on this assumption BTW - not because I suspect I may be wrong - because I don't, but because somebody else may have a more thorough and convincing argument, and my personal philosophy is not to put myself in the position of being beyond being able to be persuaded to an opposite point of view. Just sayin')

[archaos]

I ground any component part at the same ground return point as the filer capacitor from which that part is taking its power supply - following the system described in this article http://valvewizard2.webs.com/Grounding.pdf for the reasons therein. So provided that the ground return for the volume point is going to the same ground return as the filter cap from which the previous stage* is drawing its power supply, it'll probably be okay. (If the next stage comes from the same power supply node, then it probably won't make any difference)

Same thing for me, see actual circuit attached (single channel AC30 TB) :

anyway Merlin is one of my prophets 

Thanks for your explanations !