NEGATIVE FEEDBACK ON A POT?

[ViperDoc]

Even better, put it on a push-pull pot so you can defeat it altogether!

Here is an example, and where I got the idea... the AX84 October...

https://ax84.com/archive/ax84.com/stati ... 090519.pdf

Thanks for the link. Where does the NFB pot lug 1 go to, nowhere? It looks connected to the presence pot only. What if the presence pot is dimed?

[sluckey]

Where does the NFB pot lug 1 go to, nowhere?

That's right. I would connect lug 1 to the wiper.

What if the presence pot is dimed?

Makes no difference.

[beasleybodyshop]

Was/Is a very popular tweak on modded marshall type things. Dave Friedman does this on his BE100/BE50 deluxe

[MakerDP]

The presence circuit is dependent on the amount of NFB. For example, if you do decide to put your variable NFB on a push-pull pot to defeat it altogether, then the Presence knob has no effect on the tone at all.

Aiken's page has a great explanation of how they work together here...

https://www.aikenamps.com/index.php/wha ... e-feedback

Near the bottom, section called "Frequency response shaping via feedback."

And yes, that extra lug on the pot just floats. It works as an inline variable resistor, as opposed to a voltage divider like when you typically put it ground.

Rob Robinette's website also has some great info on using a 3-way switch to go between three fixed values (one of which can be defeated altogether of course.) Also worth consideration.

[jcool666]

If you're familiar with uncle doug on youtube, he adds a variable nfb control to amps regularly. He even refurbed an old electromuse from the late 40s that had a variable nfb control from the factory. They labeled it brilliance. I'm working on a champ (5F1) and planning on adding a variable nfb and presence. Ought to add a ton of versatility to a one-knob circuit.

[ViperDoc]

The presence circuit is dependent on the amount of NFB. For example, if you do decide to put your variable NFB on a push-pull pot to defeat it altogether, then the Presence knob has no effect on the tone at all.

Aiken's page has a great explanation of how they work together here...

https://www.aikenamps.com/index.php/wha ... e-feedback

Near the bottom, section called "Frequency response shaping via feedback."

And yes, that extra lug on the pot just floats. It works as an inline variable resistor, as opposed to a voltage divider like when you typically put it ground.

Rob Robinette's website also has some great info on using a 3-way switch to go between three fixed values (one of which can be defeated altogether of course.) Also worth consideration.

Thanks for the link! Lots of useful data in there.

[ViperDoc]

If you're familiar with uncle doug on youtube, he adds a variable nfb control to amps regularly. He even refurbed an old electromuse from the late 40s that had a variable nfb control from the factory. They labeled it brilliance. I'm working on a champ (5F1) and planning on adding a variable nfb and presence. Ought to add a ton of versatility to a one-knob circuit.

Uncle Doug is awesome, I enjoy every one of his videos. The dry humor is a huge bonus.