Feedback presence Q

[lowell]

I have a feedback loop with a 47k from the speaker jack to the cathode of the gain stage pre-concertina. The gain stage has a 2.2k/3.3nf on its cathode. I'm trying to determine what cap I want to bypass Rk with for a fixed presence setting. Here's my math, is it correct?

1/(2piRC)
1/(2pi*47,000*3.3nf)
=1026hz

Negative feedback at frequencies above 1khz is basically non existent right?

Or does the 2.2k play a part here? My thought is that the voltage at frequencies below 1khz is divided by a factor of 47/2.2=21.36.

[loudthud]

I think the resistor you want to plug into the formula is the 2.2K because it's the one in parallel with the cap. Think of it this way: At low frequencies the cap is an open circuit and the resistors set the feedback. At high frequencies the cap is a short so there is no feedback. In between those extremes the cap will start to come into play when it's reactance is 2.2K. With a 3.3nF, that's about 22KHz. You need a bigger cap. Maybe 68nF.