Optimal line out level for WiiM Ultra + Audiophonics MPA-S250NC?

[dominikz]

I'm pretty sure you realised I was joking before - much appreciated.

I did. But you were also right - sometimes we make things more complicated than they need to be.
Glad you found the post interesting!

 

[harkpabst]

Well, we started off with the question ...

Which setting gives you the cleanest, most dynamic result — and why?

... and the answer is indeed: It purely depends on how much power you need.

Apart from that there's no meaningful difference.

 

[Aquaman]

While we're at it. A little further up in this thread I was having a discussion with harkpabst on what line-in voltage to use when calculating the max. output voltage and watts into 8ohms. RMS or peak?

Staying with our example and using 0.5Vrms out form the WiiM into the amp with 25.5db (18.8x) gain we come to 9.4V output or 11watts into 8ohms.

Using the peak voltage (x1.41) of 0.705Vpeak we end up with 13,3V and 22watts into 8ohms.

Assuming that the speakers may dip down to 5.5ohms (a random assumption) we would end up at 32watts (peak).

So my question is are Vrms or Vpeak input the valid starting point to assess the max required power of an amp?

 

[harkpabst]

By the very definition of power you must use the effective value of an AC voltage for this calculation. Otherwise the definition of power was different for AC and DC, which doesn't make any sense.

In the case of a pure sine wave this effective value is the peak voltage divided by sqrt(2). For other wave forms the effective value would have to be calculated differently.

But as long as we are talking about a system within its limits of linearity,.other waveforms can always be created by the superposition of individual sine waves, anyway, so there is some universal truth in dealing with sine waves, only.

I don't want to introduce the peak to peak value into this discussion to not feed further confusion.

 

[Aquaman]

By the very definition of power you must use the effective value of an AC voltage for this calculation. Otherwise the definition of power was different for AC and DC, which doesn't make any sense.

In the case of a pure sine wave this effective value is the peak voltage divided by sqrt(2). For other wave forms the effective value would have to be calculated differently.

But as long as we are talking about a system within its limits of linearity,.other waveforms can always be created by the superposition of individual sine waves, anyway, so there is some universal truth in dealing with sine waves, only.

I don't want to introduce the peak to peak value into this discussion to not feed further confusion.

I understand your approach. But I'm not fully convinved.
The output voltage of an amp is also a sine wave (AC). My simplistic mind is now concluding that the peaks of this output will follow the peaks of the input. Thus assuming that the peak output voltage will be higher than calculated using a rms input voltage.

 

[harkpabst]

It does. The output voltage has a peak value as well as an EMS value as well as a peak to peak value all at the same time. There are just different ways to characterise one and the same (continuous) output voltage.

The way you look at the voltage cannot change the power output, though. Power is always energy per time and this is well defined.

 

[Aquaman]

Yeah, I think I will leave it at that. I was just trying to look at instantaneous power instead of continuous. But that may be an invalid approach.

 

[slartibartfast]

Yeah, I think I will leave it at that. I was just trying to look at instantaneous power instead of continuous. But that may be an invalid approach.

Instantaneous power is a thing but only car stereos from the 80s use it in their specs

 

[Aquaman]

Instantaneous power is a thing but only car stereos from the 80s use it in their specs

That was when I put the first power amp in my car. Combined with rear speakers into the back panel, all connected to a Kenwood cassette radio. Days of bliss and glory.