Presnce 4k7 shunt resistor

[RockinRocket]

Im wondering what exactly a higher value resistor in place of the 4k7 presence shunt would actually sound like? Lets say 10k

I'm thinking this would have less feedback as a whole.

Trying to figure out if using a larger value pot in a vintage Marshall presence circuit is contributing a small % to a beefier low end in my current build than in previous builds. Pots typically have a high 10-20 tolerance. 4k6-5k6 is what I normally measure.

[pompeiisneaks]

I can't recall the exact reason, but I do recall someone clarifying that it will make no impact. something about the way it works is that with a 4.7k resistor and the stock original pot was basically the max range of resistance that has impact on tone. Adding more resistance just means the pot's impact range is smaller, but the same effect, i.e. turning a tiny amount makes a bigger impact but the total impact is the same.

I'd bet someone remembers and can explain why lol. I'm too starting to forget too much,.

~Phil

[sluckey]

Increasing that resistor will decrease the current flowing into the PI tubes. This will lower the PI output signal.

[RockinRocket]

Slucky I need K-5 grade here
Amp will have less PI/Powertube breakuo at high volume?

[sluckey]

Increasing resistance in the blue path will cause the PI to conduct less, decreasing the outputs.

[roberto]

...and the negative feedback will increase, because the voltage divider from the output of the OT will be different.

[martin manning]

And, if you don’t change the parallel cap, the presence shelf will shift down about an octave, increasing emphasis of lower frequencies as the presence control is turned up.

[RockinRocket]

Great. So if I was to select pots that had a lower value in a vintage Marshall circuit I should be able to get a bit more drive out of the Power amp.
As miniscule as it might add I'm interested in how to fine tune the circuit.

[martin manning]

It'd be much easier to put a shunt across the pot, or adjust the value of the feedback resistor, and find out what sounds best to you.