THD questions

[draden1]

Hello,

I am looking at the differences between amps and besides power, a difference I notice is THD.  The xpa-3 states at 4 ohms it is <.1 THD and the xpa-7 at 4 ohms is .2 THD. 

Are these differences audible?  Is this something to be concerned about as I have an xpa-3 for my l/c/r but was curious about the xpa-7 for setup simplicity as I could get rid of my 2nd amp for my surrounds. 

Thanks

[DYohn]

Most people cannot detect THD below 1%, and in bass frequencies below 10%.

[dkami712]

All the emo amps have low enough distortion that it won't matter. THD below 1% is inaudible.

[draden1]

Thanks for the quick responses.

[bootman]

Some greatly regarded tube amps have as much as 10% distortion.
(and its a good thing as far as tubes go. )

But in your case, you should be fine.

[AudioHTIT]

The XPA-7 is a super choice, great power in surround, and incredible power in two channel! Go for it and don't worry about that tenth.

[pedrocols]

If I ever get into HT again I would definitely consider a XPA-5 or XPA-7. I've used a UPA-500 in the past, no longer in production, and it did pretty good!

[gzubeck]

Apr 24, 2015 11:34:01 GMT -5 bootman said:

Some greatly regarded tube amps have as much as 10% distortion.
(and its a good thing as far as tubes go. )

But in your case, you should be fine.

Tube distortion is much more pleasurable to hear due to the difference in 2nd and third order harmonic distortion. That's why tube amps for guitars are so popular. Higher distortion in solid state is not so good. The lower the distortion the better.

[audiobill]

Apr 24, 2015 11:34:01 GMT -5 bootman said:

Some greatly regarded tube amps have as much as 10% distortion.
(and its a good thing as far as tubes go. )

But in your case, you should be fine.

Please tell us one "highly regarded" tube that has 10% thd when run within design parameters.

I'm very curious.

[vcautokid]

10 percent is allot, and as modern Tube Amplifiers go, yes they can't match the linearity, and distortion characteristics of solid state, when run inside their design performance envelope it will not be 10 percent. As voicing goes even order harmonics are more pleasing to the ear as they Assonant tones vs. allot of 3rd order harmonics which when overly present are rather Dissonant tones to the ear. The Fatter sound is usually from 3rd the order side of things. But that is the thing with Tubes is their personal voice. I won't get into accuracy as such, but Theoretically if you design solid state, and tubed designs well, they should both do very well.

[audiobill]

Just one example, please.

so many bs myths, just use your ears!

[bootman]

May 9, 2015 7:10:10 GMT -5 audiobill said:

Just one example, please.

so many bs myths, just use your ears!

Here is a classic.

www.stereophile.com/content/dynaco-stereo-70-ii-power-amplifier-measurements

They do sound good.

[audiobill]

Still not there, those are past rated power, into clipping.

Perhaps another example?

Or maybe the point has been grossly overstated?

[bootman]

May 9, 2015 7:56:38 GMT -5 audiobill said:

Or maybe the point has been grossly overstated?

Ok maybe a little.

[audiobill]

May 9, 2015 18:47:53 GMT -5 bootman said:

May 9, 2015 7:56:38 GMT -5 audiobill said:

Or maybe the point has been grossly overstated?

Ok maybe a little.

Fair enough, boot!

[yves]

Electronics can generate very high orders of nonlinearity such as crossover distortion or clipping. One must be very careful in electronics design to prevent these higher orders from occurring especially at low levels. The problem is that this problem is never evaluated for electronics (well certainly never shown) and I doubt that it is even tested very often. What they do show is THD as a function of level but fail to note if the low level result is for crossover distortion or noise. If it is crossover distortion (which is very high order at very low levels) then it is highly audible even at fractions of a percent. That’s the problem with THD, it just does not show what we need to know.

Several years back I developed a test for amplifiers that used a special signal and form of synchronous averaging to measure the nonlinearity of the amp well down below the amplifier’s noise floor. This test revealed significant differences in the amplifiers as the signal level was reduced into the noise floor (the THD as the signal level is raised is again not important because it is masked and “THD + noise” at low levels, as usually shown, could be all noise). These amps all had excellent “normal” specs, but under my test they were vastly different.

Again the lesson here is that if your tests don’t work then fix them. Don’t blame the philosophy and hide behind the dogma.

Source: dagogo.com/an-interview-with-dr-earl-geddes-of-gedlee-llc