Neg. Feedback Question

Marshall Amp Discussion

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matt1969
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Joined: Tue Aug 10, 2021 10:54 am

Neg. Feedback Question

Post by matt1969 »

What kind of a change in sound would I expect if I change my neg. feedback from 47K / speaker jack to 100K / 4ohm tap?
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martin manning
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Re: Neg. Feedback Question

Post by martin manning »

matt1969 wrote: Thu Jun 29, 2023 4:11 pm What kind of a change in sound would I expect if I change my neg. feedback from 47K / speaker jack to 100K / 4ohm tap?
Similar to turning a Presence control down. IDK what tap you are on now, but going down, 8 ohm to 4 ohm, say, reduces feedback voltage 30%, so you will get increased power amp gain, reduced bandwidth, and reduced presence control effect.
matt1969
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Re: Neg. Feedback Question

Post by matt1969 »

cool thanks. i'm connected to the speaker jack & I use the 8 ohm setting with my cab.
Stevem
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Re: Neg. Feedback Question

Post by Stevem »

Here’s a simple graph that shows how that as feedback voltage increases (in closed loop) bandwidth/frequency response increases and gain goes down.

Also note case with any amp one it drops out of running in closed loop, distortion will take place much faster.
Guitarist who use their playing dynamics a lot tend to like amps better that have no feedback/ closed loop circuit.

If you play any amp loud enough that has feedback and learn to listen for this change over point then you will never not hear it again.
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