You might want to read Christian Punter of HiFi Advice's review of the STA's "little brother" the ST-10.
I think Noah is referring to Evolution STA not AMG STA.
No offense was meant - they were honest questions. The body thing was an explicit question because I *appreciate* the focus on power supply that your marketing docs have, but usually that focus also shows up with doubling between impedences.
Thanks for asking. Usually that's the case because most vendors don't design their amps (using modules from Hypex, IcePower) or power supplies. But since we design both, we tend to optimize the power of 8 & 4 Ohm (obviously speaker's impedance is not discrete, so 8 and 4 are just spec)
Lets say we start with a design with a 200W PSU. Perhaps we ended up with 100W @ 8 ohm and 200W @ 4ohm spec. If we buy off-the-shelf amp modules, that's what we ended up with. But we could also design an amp for 200W @ 8ohm and 200W @ 4 Ohm, with the same 200W PSU.
One might argue that why not put in a 400W PSU. Well, the same logic goes where you ended up with 200W@8ohm and 400W@4Ohm. So why not design an amp for 400W @ 8 & 4 ohm.
But that was dropped for the STA - I was curious as to why.
The assistant engineer forgot. I will get the info later this week. I recall it is around 750K Ohm, still very high, but not 1M Ohm.
We emphasized so much about 1M Ohm for Evolution One and AMG series, why did we drop the input impedance for Evolution STA? Well, 1M Ohm is just a number, 750K is still very large but for Evo STA design, it works better.
