Amplifier Input Impedance

Most solid state amps are designed to work with typical all SS pre-amps/systems, not higher out impedance tube pre-amps.

I think its that simple.

With ongoing popularity of tube gear in high end audio, some lines are designed with higher input imepdance to work well with tube pre-amps as well. But it is a niche market so still not as common as would be the case otherwise.

Impedance matching is important for optimal sound quality,but many might not notice otherwise or care. Plus practically its really only a significant issue when a higher out impedance tube pre-amp is involved.

How much power are you looking for ?

Good Listening

Peter

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?? ;-)

02-11-14: Bombaywalla
How come Almarg hasn't spotted this thread as yet?? ;-)

Even the great and powerful Al needs a little vacation time every now and then. ;)

02-11-14: Bombaywalla
How come Almarg hasn't spotted this thread as yet?? ;-)

02-11-14: Jmcgrogan2
Even the great and powerful Al needs a little vacation time every now and then. ;)

:-). Thanks, guys. No vacation time needed, though, as I'm always on vacation (i.e., happily retired).

Actually, I had spotted the thread. But having never designed an audio power amplifier, I can't speak knowledgeably about what the tradeoffs would be if a solid state one were designed with a high input impedance. Certainly it's readily doable, but I don't have a good feel for what the inevitable tradeoffs would be.

In addition to those tradeoffs, of course, as John and others have noted I don't doubt that in many cases a significant factor is a lack of motivation to provide compatibility with tube preamps.

Best regards,
-- Al