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What does negative feedback do?

lv

Silver Supporting Member
Messages
10,015
Would someone explain what adding negative feedback to an amp circuit does? It can be added to the preamp and power amp, correct?

Thanks
 

riffmeister

Member
Messages
16,606
adds canceling frequencies into the poweramp section.

from Randall Aiken's site:

"Feedabck: a circuit that allows a portion of the signal from a later stage in an amplifier to be "fed back" to an earlier stage, or within the same stage. Feedback can be voltage or current, negative or positive. Negative voltage feedback decreases gain, and is used to reduce distortion, flatten frequency response, increase input impedance, decrease output impedance. Negative current feedback increases output impedance, and is used in some solid-state amplifiers to obtain a more "tubelike" response. Positive feedback will increase gain, but can make a circuit oscillate if too much is applied. Sometimes a small amount of positive feedback is used to offset the reduction in gain caused by application of negative feedback."
 

lv

Silver Supporting Member
Messages
10,015
....which makes the amp run cleaner. A side effect is that it reduces brightness somewhat.

Interesting Mike....I have an amp that has a 3 position switch - no neg feedback, slight, and a lot. In the a lot setting, the amp seems the brightest.

What is the difference in adding neg feedback to the preamp vs the power amp?
 

riffmeister

Member
Messages
16,606
The presence control on a Fender amplifier is a negative feedback control, the more you turn it up, the more negative feedback it injects in the poweramp section to make the amp brighter (by canceling lower frequencies).
 




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