Amplifier Input Impedance

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

Input impedance has nothing to do with gain.

You can have a high input impedance on a solid state amp by using FET devices at the input.

Large solid state amps with a low input impedance often do have a lot of gain as they are designed for use with loudspeakers that need a lot of power. You need gain for that- 30 db might barely be enough. Conversely if you are driving a horn speaker you don't need nearly so much gain so many SETs don't have all that much- sometimes 15 db is plenty.

So there is a rough correlation but it is not based on input impedance => gain.

OK. So are not some loudspeakers designed with very low impedences so that they will audition better because they are louder? (and I understand that this is not the same as sensitivity.) Does that not relate to input impedence in amplifiers?

I'm not arguing with an audio engineer--just asking?

If I remember correctly, some years ago Mr. Wilson in an article in the Absolute Sound reported that there were some advantages to using low impedance DC coupled components in audio.