NEGATIVE FEEDBACK ON A POT?

[ViperDoc]

Is it possible to put the NFB on a pot to dial it in on the front or back of the amp?

[xtian]

Do you have a specific schematic in mind?

For gNFB, from OT primary back to PI, I've successfully used a pot in-line to adjust. But maybe LNFB is so early in the signal chain that it's more prone to interference? Probably "depends"!

[ViperDoc]

Do you have a specific schematic in mind?

For gNFB, from OT primary back to PI, I've successfully used a pot in-line to adjust. But maybe LNFB is so early in the signal chain that it's more prone to interference? Probably "depends"!

No, no schematic as of yet, but I was actually thinking of NFB, not LNFB like I asked initially. Seems like it might be cool to dial in! I’ll find a drawing later.

[Doug R.]

Sure...I have seen this done before.

[Colossal]

I do this on Plexi builds and it is a very useful mod, in my experience.

[roberto]

I do it in all my amps since 2001. Power amps have control on presence, depth and feedback.
It’s a game changer on the character of the amp and the feeling it has under the fingers.
Do not overdo: usually a 100k lin or 250k log (with a 22k in series) are the way to go if the original resistor is 47k or 100k. Define the limits you would apply by checking different resistor values, then fit the decide resistor and the pot.

[ViperDoc]

I do it in all my amps since 2001. Power amps have control on presence, depth and feedback.
It’s a game changer on the character of the amp and the feeling it has under the fingers.
Do not overdo: usually a 100k lin or 250k log (with a 22k in series) are the way to go if the original resistor is 47k or 100k. Define the limits you would apply by checking different resistor values, then fit the decide resistor and the pot.

Sounds great, thanks for the recommendation!

[wpaulvogel]

I use it and I call the control “Temper” because it controls the aggression of the amp.

[BobSimpson]

Aspen Pitman amps had a Soul control ( or something like that... ). Variable global NFB, If I remember right.

Bob Simpson

[ViperDoc]

Aspen Pitman amps had a Soul control ( or something like that... ). Variable global NFB, If I remember right.

Bob Simpson

I like it, Bob! It sounds like a no-brainer.

[BobSimpson]

Those would be Groove Tube Soul-O amps.
Should be plenty of schematics to point you in the right direction.
With my brain, no brainers work just fine...

Bob Simpson

[Travis_HY]

I added this mod to another amp build with Marshall tail and PI values recently and I forgot how great it is-particularly if you also have a 5K "scratchy pot" Presence control in the circuit as well. The negative feedback control is almost like being able to control the fidelity and frequency response of the power amp while also changing the character of the graininess of the power amp clipping itself.

Not to toot my own horn but I love this circuit...still rockin' it a year and half later. The negative feedback control is labeled "Focus" in this schematic.

[roberto]

Rivera calls ot Focus on most of his amps.

[Roe]

An essential mod if you use negative feedback. it controls response, breakup, bandwidth etc. Typically I use less NFB with a tele than with an es335 for instance.

[MakerDP]

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