How much amplifier power do you really need?

[thumb5]

There is nothing mysterious.

If you calculate power by squaring the power supply rail voltage and dividing by the load impedance, you're calculating peak power. Amplifier ratings are normally (at any rate, should be) quoted as RMS with a sine wave signal. The peak power for such a signal is exactly twice the RMS power.

Example: 140 Pro PSU rail is 41 V, so peak power into a 6-ohm load is 41^2/6 = 280 W, vs quoted power 140 W RMS.

[Pim]

All this technical stuff above goes way over my head but just below that sit my ears. And they tell me more power means better sound. So can anyone translate the above so my ears understand please?

[Jean-Marie]

Since they occur in the section for ADH config, I'm going to guess that the line for Voltage defines the setting for the class A amp which supplies the voltage and the 51 V that it shows for Jean Marie's 220 equates to the voltage for 220 W output per channel for a 220 in stereo mode. 

"Puissance" seems to translate to power. There's a setting in the configurator's speaker section where you can set maximum power output and the maximum you can set is your amp's specified power (that's also the default setting) but you can limit to to a lower output. I suspect that the 220 shown in Jean Marie's file indicates that he has chosen to leave that setting at the maximum for his 220. If you have a dual amp setup I suspect the maximum/default will be the mono output so for a 440 which is comprised of 2 220s the figure shown would be 440 which would be the power output from 51V for bridged mode for the amp.

If you limit the power output I think you'd see a lower number for Puissance reflecting the lower wattage limit you've set and that the lower output would be reached at a 0 dB volume setting. Maximum power output, whatever you set it to, will always be reached at a volume setting of 0 dB. I don't know whether the voltage value will also change if you limit maximum volume but it may also.

Basically, taken together, I think those 2 values control the settings for the Class A and Class D amps respectively given the maximum power output you choose in the speaker settings in the Configurator.

Just a guess as I said but there''s no reason to specify ADH configuration if you don't give the user the option to vary maximum power output and given the fact that the Devialet is a Class A/Class D hybrid it would seem to make sense to have separate values for the Class A and Class D stages if you are going to be able to vary output.

I've got a 140. That section of my config file shows 41 V and a Puissance of 140. I think if I added a companion to make a 210 the file would show 41 V and Puissance 210.

The logic behind your hypothesis follows but some of the math is still elusive.  Looking at the 220, max voltage is set to 51V at 0dBFS and the corresponding impedance at this voltage is 6 ohms.  Power in this case computes as 434W which is almost twice what the 220 is rated for.  @Jean-Marie suggests this to be peak power.  If we apply the math to the 140 using your figures power computes to 280W peak which is exactly twice what the 140 is rated for continuously.  If power from the Devilet 140 and 220 are not artificially limited (somewhere in the code) then where did the peak power go?

According to HiFi World the Expert 220 Pro reached a peak power of 190W into 6 ohms which is nowhere near the 434W computed from above.  @Jean-Marie suspects this is due to the evaluation unit being tested with SAM enabled. However, Audio was unable to measure the peaks of the Expert 140 Pro because the sophisticated power protection circuits prevented it...   

"It is worth mentioning the presence of a special protection circuit, which, after exceeding a certain input voltage (sensitivity), does not allow distortion of the terminals, so distortions do not increase, but stop at a level even lower than the standard THD + N = 1%. Hence, our results concern such conditions, because it is the highest power that can be obtained."

It would seem peak power may never be reached regardless of the amplifier's ability to produce it because it's trying to play it safe.  If this is true then the 220 has a major handicap.  I confirmed with Devilalet that continuous power of the 140 and 220 is as follows...

                 Expert 140 Pro            Expert 220 Pro
8 Ohms      105 W                        165 W     
6 Ohms      140 W                        220 W
4 Ohms      210 W                        330 W
2 Ohms      420 W                       330 W

If peak output power is limited to continuous output power (as multiple tests have shown) because of the protection circuits then that can be a problem for people with speaker impedances that dip below 3 ohms and mine do.  For the people that still believe more power sounds better than less power, have some crow.

I think peak power can be reached for a very short amount of time. you really need to take the crest factor into account. Once again for a pure sinusoidal tone, the peak power is twice the RMS power and RMS is always what is stated.

I did a bit of experimentation with the configurator on the D250 which is an interesting case:

For a D250 stereo, the ADH sections is:
"ADH_CONFIG":{
    "VOLTAGE_0DB":55,
    "PUISSANCE_0DB":250
  },

And for the D250 stereo, the same section becomes: 
"ADH_CONFIG":{
    "VOLTAGE_0DB":55,
    "PUISSANCE_0DB":1000

55V under 6 ohms is a power of 504W, so about twice the rated 250W RMS

The way you bridge your amplifier (turning it into mono) is that instead of connecting your speaker between the black post (connecting to the ground) and the red post (swinging between -55V and +55V) is that you connect it between the two red posts and you invert one channel. So each red post still swing between -55V and +55V, but because they are in opposite phase, the difference between the two is not double, swinging between -110V and +110V between the two.
Guess what, 110V is 2016W under 6 ohms, giving once again the rated RMS power of 1000W for a pure sinusoidal tone.

@RebelMan what does continuous power means? I am reading as RMS power on a pure sinusoidal tone (or tones) that the amplifier can provide on a continuous basis. With that meaning, the peak power of such signal would still be twice the RMS power. This is intrinsic to the nature of the Sinus.
The only way for it not to be true would be to use a very different kind of signal where the crest factor would be much lower than 3dB, which is possible but quite unlikely in my mind because it would be very different from any measurement protocol of audio equipment that I know of (but I'm not pretending to know every one of them.)

Jean-Marie

[thumb5]

Nigel Tufnel's take on it: https://www.youtube.com/watch?v=KOO5S4vxi0o.

[Confused]

   

[RebelMan]

There is nothing mysterious.

If you calculate power by squaring the power supply rail voltage and dividing by the load impedance, you're calculating peak power.  Amplifier ratings are normally (at any rate, should be) quoted as RMS with a sine wave signal.  The peak power for such a signal is exactly twice the RMS power.

Example: 140 Pro PSU rail is 41 V, so peak power into a 6-ohm load is 41^2/6 = 280 W, vs quoted power 140 W RMS.

Your math agrees with the calculations I posted, in theory.  In practice, however, peak power is not being reached because of hidden code or the protection circuits are kicking in too soon preventing it.  Audio tested the 140 and could only produce 102 W in to 8 ohms and 203 W into 4 ohms before the protection circuits kicked in.  This was also the case with the 220 when HiFi World tested it, "...using 0.2 sec sine wave bursts, power measured 144 Watts (34V) into 8 Ohms and 290 Watts into 4 Ohms.  Into 6 ohms, burst power is 190 Watts, slightly below the 220W figure quoted but not a consequential shortfall."   

Using theses figures in your example the math becomes... 220 Pro PSU rail is 34 V, so peak power into a 6-ohm load is 34^2/6 = 192 W, vs quoted power 220 W RMS.  Which again supports the observation that peak output power is being limited to continuous output power levels.

[RebelMan]

All this technical stuff above goes way over my head but just below that sit my ears. And they tell me more power means better sound. So can anyone translate the above so my ears understand please?

Yes. Your ears lied!  

[petrik]

There is nothing mysterious.

If you calculate power by squaring the power supply rail voltage and dividing by the load impedance, you're calculating peak power.  Amplifier ratings are normally (at any rate, should be) quoted as RMS with a sine wave signal.  The peak power for such a signal is exactly twice the RMS power.

Example: 140 Pro PSU rail is 41 V, so peak power into a 6-ohm load is 41^2/6 = 280 W, vs quoted power 140 W RMS.

Your math agrees with the calculations I posted, in theory.  In practice, however, peak power is not being reached because of hidden code or the protection circuits are kicking in too soon preventing it.  Audio tested the 140 and could only produce 102 W in to 8 ohms and 203 W into 4 ohms before the protection circuits kicked in.  This was also the case with the 220 when HiFi World tested it, "...using 0.2 sec sine wave bursts, power measured 144 Watts (34V) into 8 Ohms and 290 Watts into 4 Ohms.  Into 6 ohms, burst power is 190 Watts, slightly below the 220W figure quoted but not a consequential shortfall."   

Using theses figures in your example the math becomes... 220 Pro PSU rail is 34 V, so peak power into a 6-ohm load is 34^2/6 = 192 W, vs quoted power 220 W RMS.  Which again supports the observation that peak output power is being limited to continuous output power levels.

Do you know were these measurements done properly - like was the SAM turned off? The SAM can limit the power.

[Pim]

All this technical stuff above goes way over my head but just below that sit my ears. And they tell me more power means better sound. So can anyone translate the above so my ears understand please?

Yes. Your ears lied!  

It must be the two instead of one power cords that you use with dual mono that makes the difference then. My ears don’t lie. It’s like listening to my dog barking versus the labrador next door. It’s different.   Clearly

[Gerronwithit]

Between -20Db and -13Db, below that I have drunk too much. I find that a mathematical solution promoting huge peak power to guarantee some sort of musical or aural integrity very dubious.