> a physics major
> it seems as if there's several stages of amplification
You studied "beams"? Bridges and such? Truss, but also just plain solid beams.
Look under your house. There's a beam down the center of the cellar. Above that are more beams (joists) crossways to the center beam. Above that is floorboards, which obviously act as beams when you stand between joists. Three whole layers of beams in a simple house floor.
Go out to a real bridge. Your basic bridge is two long steel or concrete beams which are also the side-walls of the roadway. To fill the gap between they use cross-beams, maybe every 4 feet. Then they run smaller beams (possibly rippled steel sheet) lengthwise to bridge the 4-foot gaps.
A Physics Degree should touch on beams but not when and why you might have beam upon beam. You get this by plagiarizing the works of others with more knowledge than a physics major. Much classical mechanics (what physics was before Rutherford and Einstein) consisted of explaining what untutored builders were doing. (And one of the Greats published an analysis of the Cantilever which was just wrong; it bothered physicists for years but carpenters mostly got it right.)
We "could" build a house-floor with one solid hunk of wood. Obviously it would be 30'x24' LxW, and when you estimate stiffness across a 30' or even 24' span you will want to go over a foot thick or it will come out floppy. Aside from the shortage of 24' diameter trees and the many 13' underpasses between forest and home-site, the cost and weight would be humongous.
With common building materials, a multi-beam layered approach gives best economics between point/line supports and a continuous surface (floor). Diaphragm, little beams, big beams.
OTOH, some short narrow highway bridges are built as a "single slab".
And I have heard of roofs built with a single slab of foam plastic, in places so hot that the desired insulation happened to exceed the required strength and foam plastic price was low.
> several stages of amplification
The total available power gain of a single tube or transistor is 40dB-50dB. It isn't ready to work as-is: bias and load networks tend to suck-off gain. Power gain of 20 in one device is doing good.
The gain is variable from one part to the next, we may want to slug-down the circuit so that device tolerances are overwhelmed by more-precise passive components.
We also like to have "mismatch" between one box and another so interfacing does not require annoying computations; this really means having way-extra total power gain available. In terms of beams: "stiff".
A complete audio system, from passive pickup (e-guitar, microphone) to useful output (loudspeaker) has voltage gain of 8V/0.01V or 800, current gain of 1A/0.000,000,05A or 20,000,000, total power gain 16ee10 or 102dB.
Clearly the whole system needs ab-minimum 3 devices. Fender Champ and the cheapest tube tape players are examples. It is more likely to have 102dB/20dB= 5 devices. Single-device POWER stages (where signal power is not teeny compared to device ratings) have issues; tube amps above a certain size and transistor power amps generally have at least one stage using two devices to push-pull. A basic 1972 hi-fi with Phono input might have 8 devices in 6 stages.
We often like to break the whole system into separate boxes, or at least with patch-points to break-in and go-out to external boxes. Interface simplicity suggests additional stages so that outputs can drive unknown loads and inputs will not load-down unknown sources. This often leads to more total stages and devices.
The art of electronics is putting these many stages together nicely.
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