Negative feedback

So I have a Music Man HD-130 210 with the 12ax7 P.I. that I got a little while back. The previous owner installed a neg. feedback switch on the amp. Stock is negative feedback on and when you throw the switch there is no neg. feed back. My question is what exactly does this do and what exactly is neg. feedback and impact on sound without ?
Thanks


Edit:
I'm getting some answers on the Shock brothers section.

I'm lost. If you have the amp, why don't you know what the sound difference is with the switch on/off? Throw the switch and tell us:)

A negative feedback loop takes negative energy from the speaker and feeds it back into the circuit at the phase inverter/driver. The effect is partial phase cancellation (the negative feedback is out-of-phase, relative to the "regular" signal), resulting in greater clarity and less distortion. A flick of the switch will be a better description than words, but that's what's going on. It depends on the amp, how "hot" you're running it and what you need whether negative feedback is desirable or not.

I did this on a blues jr. At lower volume with no NFB, it sounded bigger and looser and a hair noiser. For the blues jr, no NFB at low to mid volumes made it a boutique amp. Also increases the touch sensitivity. Got rid of the boxy sound.

But if playing with a lot of people and loud, you probably want NFB because it keeps the amp tone more focused and less extreme excursions especially on the low end (or at least turn the bass down).

You can also put in a variable resistor and dial in what you like.

I'm lost. If you have the amp, why don't you know what the sound difference is with the switch on/off? Throw the switch and tell us:)


I think he meant the electro mechanics, he obviously can hear it. :rolleyes:


:mrgreen:

Negative feed back loop... Usually the missing link in amps claiming to be class A.

I think he meant the electro mechanics, he obviously can hear it. :rolleyes:


:mrgreen:

thanks, I wasn't going to state the obvious :smile: