Author Topic: Amp-in-a-pedal and negative feedback  (Read 250 times)

Max

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Amp-in-a-pedal and negative feedback
« on: March 14, 2020, 05:09:51 AM »
Hi All, I've had some experience building some distortion pedal derived from famous amps, especially from runoffgroove, and after experimenting with my take on the Orange MkII (check the 2019BOTY contest for more) I'm now trying to understand a bit more about the negative feedback.
From what I get, this is used to bring part of the signal from the output transformer back to the cathode of one of the preamp valves, where the signal phase is opposite w.r.t. the anode, in order (for example) to tame the highs or increase/reduce the distortion.
Now, some of the older projects from runoffgroove (i.e. Professor Tweed, Thunderchief and Flipster) as well as the orange project I started from, follow the original amp schematic 1:1 leaving out the final tubes and the output transformer, but include the negative feedback which, instead of taking the signal from the output transformer, takes it from the output of the pedal, which, correct me if I'm wrong, is equivalent to taking it from the output of the preamp.
My question is: without the output transformer, doesn't the negative feedback just suck signal from the output without really affecting the tone as in a real amp? Maybe this is one of the reasons runoffgroove moved away from this 1:1 philosophy to get better sounding circuits in terms of fidelity to the inspiring amp.
EDIT:
this is probably the best explanation I've seen of the negative feedback:
https://youtu.be/H5fFb5_9xyA?list=PLhv-fcfLlQdrnP4wn5wWaaO8_Y8IFrPxx
« Last Edit: March 14, 2020, 06:30:33 AM by Max »

koolaide

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Re: Amp-in-a-pedal and negative feedback
« Reply #1 on: March 14, 2020, 06:09:39 AM »
It is my understanding that negative feedback is simply an out of phase signal that is fed back into the circuit usually to help stabilize the circuit / control gain.  Others that know more will respond.

Cheers,
Jim