I have built hundreds of audio circuits with BC549 and 2N3904 transistors. Usually the frequency response is absolutely flat up to 400kHz. Their hfe (AC current gain, not voltage gain) is 330 at 1kHz and drops to 1 at typically 200MHz.
The circuits have never had trouble with feedback or spurious responses even when two high power AM radio stations are next door or 30 high power FM radio stations are next door.
The circuits have never had trouble with feedback or spurious responses even when two high power AM radio stations are next door or 30 high power FM radio stations are next door.
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