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Discrete transistor based circuits can not run at very high frequency due to the capacative loading and possibly other issues like propagation delays.
Talking specifically about discrete transistor circuit based BJT amplifiers, is there any use of them besides making audio amplifiers?
The keyword here is "discrete" transistor circuit that is "analog circuit" and not IC design or digital design.
BJTs are used in a lot of applications, from DC to microwaves.
Some low frequency applications besides audio are DC amplifiers, voltage regulators, function generators, and video circuits. Linear power supplies use BJTs as pass elements, as well as for error and reference amplifiers.
At higher frequencies they are used as RF amplifiers, both in receivers and transmitters. They are used as RF power amplifiers up to kilowatts of power. BJTs exist that function into the hundreds of Gigahertz frequency range.
Think of almost any electronic device made around 50 years ago (between the time vacuum tubes were dominant and the time ICs became prevalent) and it probably used bipolar transistors.
I'm a scientific instrument designer: I don't do audio. I use plenty of BJTs in many roles. Advantages of BJTs relative to FETs include:
Besides the historic use of BJTs in TTL logic, there is an inherent problem with hFE Max/min ratios in production. Some companies such as ROHM specialize in binned BJTs with low hFE ratios and essentially lead the industry in digital transistor switches.
Naturally, BJTs have been used for many applications such as RF, high-speed analog switches using common base mode with many for multiplexing channels or level shifters and high voltage switches with FET inputs called IGBTs.
Early Scopes and TVs used BJTs for everything from power supplies, voltage regulators, video clamps, video DACs, high-speed SRAM, and hundreds more applications.
You can review ROHM's digital transistor options here. https://www.rohm.com/products/transistors#bipolar-transistors
Solutions include: https://www.ecstuff4u.com/2018/05/application-of-bjt.html
Socratic search method of using coarse then finer search and answers in a web search.
e.g. web search
W. K. C. Guthrie in The Greek Philosophers sees it as an error to regard the Socratic method as a means by which one seeks the answer to a problem, or knowledge. Guthrie claims that the Socratic method actually aims to demonstrate one's ignorance. Socrates, unlike the Sophists, did believe that knowledge was possible, but believed that the first step to knowledge was recognition of one's ignorance. Guthrie writes, "[Socrates] was accustomed to say that he did not himself know anything, and that the only way in which he was wiser than other men was that he was conscious of his own ignorance, while they were not. The essence of the Socratic method is to convince the interlocutor that whereas he thought he knew something, in fact, he does not."[8]
I conclude that this Socratic (web search) Method should be better called the Guthrie Method. Assume you know nothing about the answer. Whereas this site uses experts who know something about the answer but the question needs better scope details prompted by comments. (Socratic Method).
There is an online electronic simulator written by a programmer named FALSTAD. You will find lots of basic designs built in to simulate.
It can do FFT and users can choose hFE , but it is constant not nonlinear when saturated to 10% of hFE.
For what it's worth I can say that I've built AM radio amplifiers with the common & ordinary 2N3904 BJTs.
Even a transistor with a fT of only 300 Mhz like the 2N3904 can easily handle up to 10 Mhz (and more with good design), let alone AM radio up to 1.7 Mhz. The discrete design of Common Emitter between Emitter Followers worked great, whereas if I had used ordinary Op Amps - it wouldn't have worked, because an Op Amp with a 3-4 MHz bandwidth probably can't amplify more than 0.5 Mhz and even that's a lot for such Op Amp. I might have needed a more expensive Op Amp that's also not available for breadboards (in DIP form).
The main point also is that inside chips it's the same BJT transistors in the same configs as used or could be used discreetly. Broadly speaking, there isn't one design in chips and another discreetly. It just a matter of form factor.
In particular, while discrete designs are not associated with a feedback loop as often, all the same feedback is not a chip property and could be added discretely just as easily - I've had a chance to build a 15 transistor BJT OP Amp discreetly and used it in negative feedback configs - by wiring the output back to the inverting terminal.
On Mouser and Digikey there many BJTs with transition frequencies of dozens of GHz (& accordingly they have a much lower capacitance than ordinary).
The transistors inside chips also don't have very different capacitances than discrete ones, & as a result are limited in frequency in a similar way to discrete ones. Although the more compact form factor of ICs helps with transmission line issues.
