Amplifier Input Impedance

I have to try again. I have the same complaint on low impedence SS amps and have spent years trying to match preamp to amp. I think that the lower the input impedence, the more gain the amp has which in turn degrades sound quality. For better SQ you want low gain in amp and pre. So if company X wants to make a 200w amp, it is easier accomplished by making the amp low impedence at the input. But I don't have the technical knowledge to prove this or discuss it.

And I haven't had to deal with this issue since I got my hk990 integrated. It has a variable gain setting for the active pre which doesn't address the issue of amplifier input impedence directly (and hk doesn't say what the amp's input impedence is and hopefully hk has matched pre and amp), but it does provide a tool that affects impedence in regard to the speakers so that gain can be adjusted according to the speaker demands. If you had speakers that were 16 ohms which you could get with autoformers, a SS amp would have a lower power output.

But again I have the same complaint. Amps get gain and hence power depending on their input impedence. I'm sure someone can explain this better.

It is true that the Hovland has a pretty nasty output impedance which is just as unforgivable as exceedingly low input impedance monster amps. My point is only that this hobby hs quite enough challenges in producing great musical sound in the home, so why do some designers complicate matters with silly impedance design.

For example, the Bryston "Flagship" 28B SST2 mono blocks spec at 15,000 ohms. The Aragon Iriduim, same input impedance. These are just two examples (not trying to beat-up on these companys); there are many many other examples.

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?? ;-)