Non-practical Question - Input Impedance/other input circuit behaviour

[JimChjones]

This is just a desire for random knowledge question, not in any way a practical query, and its probably for the serious amp designers.
Simple minded amateurs like me tend to think of electronic circuits as everything happening in one direction from input to output. I had my mind somewhat blown as a teenager when I learned that the cabinet affected the impedance of the speaker, and even more blown when it occurred to me that this must also affect the output power of the amplifier at different frequencies. I think I understand from @agedhorse posts that the effects can be rather more complex than that. So I've recently got to wondering: how far back into the amplifier do such effects reach? Do they even get as far as the preamp or even the input circuit?

Oh, and is input impedance a constant or does it vary with frequency, and do the characteristics of the instrument affect the input circuit behaviour? I hope these questions aren't too compromised by ignorance/naivety to be answerable.

Jim C

 

[agedhorse]

It depends on the design, but yes the input impedance of an amp can be affected (slightly) by the load. This is sometimes referred to as reflected impedance.

input impedance of an amp can certainly vary with frequency (and usually is to some extent).

 

[Old Garage-Bander]

This is just a desire for random knowledge question, not in any way a practical query, and its probably for the serious amp designers.
Simple minded amateurs like me tend to think of electronic circuits as everything happening in one direction from input to output. I had my mind somewhat blown as a teenager when I learned that the cabinet affected the impedance of the speaker, and even more blown when it occurred to me that this must also affect the output power of the amplifier at different frequencies. I think I understand from @agedhorse posts that the effects can be rather more complex than that. So I've recently got to wondering: how far back into the amplifier do such effects reach? Do they even get as far as the preamp or even the input circuit?

Oh, and is input impedance a constant or does it vary with frequency, and do the characteristics of the instrument affect the input circuit behaviour? I hope these questions aren't too compromised by ignorance/naivety to be answerable.

Jim C

In electronics and especially seen in speaker specs, impedances are "nominal", in name only.
Impedance, by its very nature, is frequency dependent.