Negative feedback in preamp pedals

[Mike McLane]

I still have a love of my old 5F6 Fender Bassman. If you were to build a preamp pedal how could you emulate the negative feedback loop?

 

[RetiredUnit1]

Well, the NFB is part of the power tube circuit, not the preamp. It's the signal, inverted but at a lower power so it cancels some of the signal, modifying the resistance modifies how much is cancelled.

I'm getting ready to build a bassman 5F6A with a three way NFB resistor switch, the Bassman value, the JTM45 value and zero resistance for a 5e3-ish sound.

Being new to pedals, I'm assuming you'd want to use a pot to modify the breakup? I don't post much about stuff like this 'cuz it's better to remain silent and appear ignorant than to talk and remove all doubt

I got the mod from Rob's page, https://robrobinette.com/5F6A_Modifications.htm#3-Way_Negative_Feedback_Switch

but made my own layout

 

[Mike McLane]

I was thinking of strictly a tube preamp pedal like Sushi makes . . . no output stage. So there’s nothing to draw a feedback loop from. Just wondered if there was a way to mimic it in a “preamp only” format.

 

[owlexifry]

I was thinking of strictly a tube preamp pedal like Sushi makes . . . no output stage. So there’s nothing to draw a feedback loop from. Just wondered if there was a way to mimic it in a “preamp only” format.

https://robrobinette.com/Voicing_an_Amp.htm#Preamp_Local_Negative_Feedback

 

[vigilante398]

I still have a love of my old 5F6 Fender Bassman. If you were to build a preamp pedal how could you emulate the negative feedback loop?

@owlexifry (and also Rob R. obviously) nailed it there, resistor in series with a cap between the plate and grid of one of the later stages of the preamp is the closest you can get without a power stage.

 

[Mike McLane]