Amplifier Input Impedance

Stickman451,
it's easy to levy the blame on the low impedance of the power amplifier but your Hovland HP-100 is also to blame. It's output impedance is 2500 Ohms i.e. 2.5KOhms. That's really high for a tube amp (but maybe normal??). I've seen an ARC Ref3 have a 600 Ohm output impedance, my CAT SL1 has a 100 Ohm output impedance, several Audio-Note (UK) preamps are xformer coupled to have low output impedance. SO, I know that it's very possible to have a low output impedance tube pre - the HP-100 is not one of them tho'.

Obviously you want to keep the HP-100 so it might be worth exploring a buffer stage between your pre & yet-to-be-purchased solid-state power amp?

Recently I was in the hunt for a really good set of 'muscle amps' to use on my Magnepan 20.7's and it was a little frustrating to see just how many big-name powerful SS anps have atrociously low input impedance.

can you please let the forum know which solid-state power amps you researched? And, how "atrociously low" their input impedance was?
Thanks.

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?? ;-)

help me out here, what is 1/10th of 100kohms?
Audiolabyrinth

that would be 100KOhms = 100,000 Ohms divided by 10 = 10,000 Ohms or 10KOhms.

The general principle here is that when the output impedance of the preceeding unit is 1/10th the input impedance of the proceeding unit, the output impedance of the preceeding unit has little effect on the (music) signal transfer - you get 90%+ of the (music voltage) signal to transfer & there is (very) little loss.
hope this helps.