Musical Power

Just how much power can you expect to get out of your little Sonic Impact amp?
Tripath rates the chip at 6 watts per channel continuous into 8 ohm with 0.1 THD.
See these measurements.
I can tell you that the new Sonic Impact version of this amp begins to clip at about 10V P-P. So that does work out to about 6.25 watts RMS into 8 ohms. My early measurements showed 8V peak, but better power supplies seem to help - a lot.

Why won't you get the full power rating out of this amp (or any other) on a musical signal? It has to do with the very nature of music and the way that CDs are recorded.
6 watts RMS is the MAXIMUM value that his amp can supply without terrible distortion and clipping. All music should be BELOW this peak level. Here is why.

With digital sound it is very easy to determine what the absolute maximum level is. When all bits equal 1, then the highest level has been reached, the output simply can not go any higher. Now that we know what this absolute maximum is, we can work backward toward an average musical level. We will call this maximum level 0 dB.

Of course music is not recorded at peak value all the time. But where is it recorded? Mostly at -18dB RMS below peak. This is the standard for most popular music. For classical music the average level is -22 dB below peak while modern pop mixes are "hotter", at -15dB. This is very consistent across all CDs, as it is the industry norm for mastering. FWIW, heavy metal is even hotter than pop, with an RMS value of -10dB. Very little dynamics there, but plenty of sound to bang your head by.
Now that we know that music is generally 18 dB RMS below maximum or 0dB, we can calculate an average musical power level.

Let us take the Tripath chip as an example. It can deliver about 10V peak before clipping. Let us take this 10V maximum level before clipping and call it 0dB. The average musical signal is 18dB RMS below this. Thus: 10V -18dB (RMS) = 1.25V.
That's 1.25V RMS, as the -18dB below peak is an RMS value. The peak is 0dB (10V) and the average level is -18dB (1.25V RMS).

1.25V RMS into 8 ohms will give us… not much. Only about 0.2 watts RMS. about 1/5th watt or 0.4 watts RMS into 4 ohms. That's all.
So if you want to run this amp WITHOUT CLIPPING, average musical power will be only 1/5th watt. (More or less depending on the music you like, see above)

We can see from this that you will need some pretty efficient speakers if you hope to run this amp at a realistic listening level. These calculations apply to any power amp, just change the maximum peak value to suit. You can also calculate in the other direction to see how much power you might need with a certain set of speakers.

You can always push the amp louder, it can supply the power up to about 6 watts. But if you do push it, it will clip the peaks. This clipping does not sound pretty on the Tripath chip. On a good old tube amp the clipping will be nicely rounded and will not sound nearly as bad, as harsh. That is one of the main reasons why tube amps of an equal power sound more powerful than a SS amp. You can push the average level up higher before clipping starts to sound awful.

But as long as the peak clips are few and far between, you probably won't notice them. So you can cheat, a bit.

Summary:

10 V peak before peaking.
7V RMS before peaking
6 watts RMS into 8 ohms.
0.2 watts/channel average musical power
before clipping into 8 ohms.