NFB wiring question

[catalin gramada]

Hello. For a new project I want to mount the nfb series and shunt resistors directly onto the speaker jack then to run a twisted pair to the relative tube grid and its ground point. The shunt resistor will be 100 ohm or so tied to the speaker jack , then 10-12 inch of twisted wire back to inverter grid and its grounding point. My question is should I add a parallel -with shunt 100ohm- grid leak to the tube ( say 100k-1M) close to the tube socket ? or should I add a ( say 100k) grid stop resistor ? Just asked to avoid from the plan any stability problems caused by the layout please ... Thanks.

[Helmholtz]

Not clear. Please post a drawing.

[catalin gramada]

I.m in traffic so I cannot make it mare clear. Hope is readable.... grid stopper and grid leaks help to improve potential problems please ? Thx

[Helmholtz]

Info not sufficient. Need to see the PI wiring.
Isn't the 100R NFB shunt resistor part of the tail?

[catalin gramada]

No. Nfb goes just into the grid of non inverted stage. I have a ccs in cathodes. I just want to af a grid leak and a grid stopper to the non in erted input/ nfb point. Without nfb those input is directly tied to grou d Does it worth ?

[catalin gramada]

Want to make oth inputs more symmetrical. I have 1M into inverted grid and 100 ohm shunt nfb at the end of 30 c of twisted wires in the non inverted grid

[Helmholtz]

If it's a LTPI the grid will sit at some elevated DC. So a grid leak to ground makes no sense. Except if you're using a negative tail supply?
I hate to speculate without seeing a schematic.

Why don't you use a shielded cable instead of the twisted pair?
I would be more concerned about creating a ground loop than instability.

[catalin gramada]

There is no a loop in grounding. The OT common will be grounded just through the nfb return which is tied just to the relative ground of the stage where nfb is applied. Forgot the inverter and consider nfb is applied to any gain stage to make it simpler please

[catalin gramada]

I don't have a stereo shielded cable for wiring . Mono shielded meant the nfb return will run through the shield...no good

[Helmholtz]

Mono shielded meant the nfb return will run through the shield...no good

Who says so?

If one of your wires is at ground potential it doesn't need a shield.
Shielded cable is always better than a twisted pair in unbalanced connections.

[catalin gramada]

I make it more clear I hope. Does it make any sense to use a grid leak and a stopper ? This circuit make no sense of course but simplified just to ideea to treat non inverted stage input as any input of whatever gain stage

[catalin gramada]

This is the inverter I want to apply, kind of... considering 1k series and 47ohm shunt tied directly to the output jack socket

[Helmholtz]

I don't see a reason not to use a shielded cable here with shield connected at both ends.
This is assuming your output jack has no chassis ground connection.

The 1M grid leak is not necessary as there's already a DC path from grid to ground.

Not possible to predict if there's any benefit from a large grid stopper here.

[catalin gramada]

I don't see a reason not to use a shielded cable here with shield connected at both ends.
This is assuming your output jack has no chassis ground connection.

The 1M grid leak is not necessary as there's already a DC path from grid to ground.

Not possible to predict if there's any benefit from a large grid stopper here.

The output jack ground is a signal return point, I don't see any reason ever to be conected to chassis but to the signal ground instead. Of course using nfb will be returned to it relative grounding point

[Helmholtz]

Just mentioned it to make sure.
Many commercial amps use a chassis grounded output jack though it could be avoided.