Amplifier Input Impedance

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.

http://www.audioholics.com/audio-amplif

The above site agrees with some above comments from Bombaywalla and others. To summarize, according to the source, high input impedence in SS causes high voltage gain which in turn causes noise. It can also cause bandwidth to decrease. And finally it can introduce DC offset.

My head is still spinning from trying to absorb what I read in 15 websites which destroyed my misconceptions.
But apparently high input impedences can cause more harm than good.

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?

Not really. The fact of the matter is that all amplifiers have less distortion driving higher impedance speakers. Some speakers are lower impedance as some solid state amps will make more power (sound quality is being traded off for sound pressure in this case). Many speaker designers don't realize that though. And this **is** in fact what we are talking about with the term 'sensitivity'. But none of that has anything to do with the input impedance of an amplifier.

www.audioholics

The above site agrees with some above comments from Bombaywalla and others. To summarize, according to the source, high input impedence in SS causes high voltage gain which in turn causes noise. It can also cause bandwidth to decrease. And finally it can introduce DC offset.

This is mostly bogus! Input impedance has 100% nothing to do with gain. A high input impedance does not have to have anything to do with noise either unless the design and execution is shoddy. We get 300KHz with 100Kohm input impedance, clearly the bandwidth thing is problematic. Think about a 6AU6 vacuum tube which is very high impedance but can operate easily at 10MHz. Finally, input impedance has nothing to do at all with DC offsets, and cannot introduce it.

I would stay off that website as it is a source of misinformation, and that is being kind.