Building a preamp with presence/depth

[nickbme07]

Hi guys maybe you can help me here. I'm trying to build a preamp having presence and depth controls, without having the power section locally (circuit is pre PI and imto refurn fx.of an amp). Am I on the right track using the inverted signal from the first cathode follower (v2, v1 is not on diagram) as a negative feedback source? Coming from pre-tone stack, does this cause any problems that the normal output is different than the 'NFB'? I havent gotten any voltage readings yet so the resistance values are probably off and not sure if i need 'mixin resistors' at end. Any suggestions here, these are new grounds for me! Thanks in advance!

[Helmholtz]

I don't see much sense in such project.
Basically a presence control is just another (though active) treble control in the power stage, while a depth control is another bass control.
Their special sonic effect is due to the placement after the preamp and the interaction with the NFB (output impedance, damping factor) and power amp distortion (clipping behaviour).

[nickbme07]

Unfortunately I am not very versed in original design - and I am trying to 'port' over a schematic from solid state to tube.
Attached you can find where the depth and presence controls are emulated with TL072's.
I've managed to implement the depth and presence controls to the end of my tube preamp circuit, which obviously just gives the opposite output of what I want - This was a test. Now I have to move that to an inverted source and have it mixed back in, balanced, with the output. This in mind will act as a NFB and create the canceling effect emulating the depth and presence controls. But as I mentioned, I wasnt sure if pulling the signal pre tone-stack will have an impact of the final cancellation and how to get this implemented 'globally' keeping impedances correct.

[Helmholtz]

I don't understand your drawing. Where does the NFB signal come from?
What does the circle mean?

[nickbme07]

I think what you are asking, is the output. The NFB comes from the v2a grid (first stage in this schematic, v1 not shown).

[Helmholtz]

Still don't understand. What is the circle at the output?
NFB signal must come from the output.
Your phase relations look wrong.
A cathode follwer doesn't invert the phase, so the grid and cathode signals of V2b (and V3b) must be in phase.

[nickbme07]

Ah, you are right - I have the tap in the wrong spot. The phase is inverted after both stages, because its a DC coupled Cathode follower.. Let me go back to the drawing.

[nickbme07]

How does the NFB work here in the preamp? Am I not able to do similar?

[Helmholtz]

How does the NFB work here in the preamp? Am I not able to do similar?

Feedback means sending a signal back from an output to a related input.
In the example the output is the plate and the input is the grid of the first triode.