NFB question 2204

[joesatch]

I know this board focuses more on fender style builds but i feel there is more knowledge here than other boards. I'm putting this depth circuit on my NFB.  The 2204 build has a 100k NFB resistor on the board. I'm going to run KT77's.  Should i be replacing the 100k with a 47k and running the NFB out from the depth circuit to the 8 ohm tap? This is a high gain build with switchable Jose clipping, additional tube SIR #36 stage as well as other component changes for high gain.

[sluckey]

The original uses 100K connected to the 4Ω tap. Changing to 47K and connecting to the 8Ω tap will give very similar results. But since you are adding the resonance circuit into the NFB line, you may just want to experiment with the 100K resistor until you find a value that suits your ears.

[pdf64]

The original uses 100K connected to the 4Ω tap. Changing to 47K and connecting to the 8Ω tap will give very similar results…

My thinking is that a 47k series feedback resistor sampling the 8ohm output will result in quite a bit more NFB being applied than using a 100k resistor sampling the 4ohm output.
Might you have been thinking of 100k resistor sampling the 16ohm output?

… I'm going to run KT77's.  Should i be replacing the 100k with a 47k and running the NFB out from the depth circuit to the 8 ohm tap? …

Are you asking because you’re changing the output valve type, or because you’re tinkering with the feedback network?
If the former, on the face of it , there shouldn’t be much difference, as the two types have broadly similar gm and gain factors.
If the latter, yes, the stock degree of NFB is pretty low, so to make presence / resonance controls more effective, a greater degree of feedback may be useful.

[joesatch]

adding more nfb and changing tubes both 

[sluckey]

The original uses 100K connected to the 4Ω tap. Changing to 47K and connecting to the 8Ω tap will give very similar results…

My thinking is that a 47k series feedback resistor sampling the 8ohm output will result in quite a bit more NFB being applied than using a 100k resistor sampling the 4ohm output.
Might you have been thinking of 100k resistor sampling the 16ohm output?

I said that backwards. Thanks for proofreading.

[PRR]

>47k ...sampling the 8ohm  .... 100k resistor sampling the 4ohm

Also note that the voltage ratio from 4Ω to 8Ω at the same power is 1.4, not 2.

[joesatch]

i'm going 100k into 8 ohm. Will test with 47k after build is complete