02-10-14: Cobra2
Low input impedance is an advantage regarding noise...
I might be missing something here but in an audio power amp we are considering only voltage gain & not power gain. So, how does input impedance factor into noise when we are considering only voltage gain (in an audio power amp)?
02-10-14: Arnettpartners
I should keep my mouth shut because I'm ignorant, but I have read that it's hard to design a SS amp with high input impedence and still get enough power or ...
again, I could be missing something - how does input impedance figure into the voltage gain of an audio power amp? If we were talking power gain then I could see input impedance figuring into the overall (power) gain calculation.
02-10-14: Atmasphere
Stickman451, you are correct as is Jmcgrogan2. Its easy enough to design a solid state amplifier with a high impedance input (100K);...
so, what sets the input impedance of an audio power amp?
My understanding was that an audio power amp's input impedance could be increased by using global negative feedback (which is a no-no 'coz of all the other issues this brings with it) & by selecting the type of semiconductor device used for audio power amplification. If the designer uses BJTs the input impedance is going to be lower than if the designer used a MOSFET or even a JFET. What are the ways to make it arbitrarily high in a s.s. amp?
In tube amps this might be different as the designer can put a resistor of arbitrary large value in series with the tube input. Is that why you say that the amp input impedance could be arbitrarily high, Ralph/Atma-sphere??
How come Almarg hasn't spotted this thread as yet?? ;-)