Class D Amp Specs

[Deward Hastings]

Re: Class D Amp Specs

OEM Class D amp manufacturer's are often of the opinion that there is too much emphasis on amplifier distortion figures, considering the level of distortion in loudspeakers is much higher.

There is also the argument (probably more correct than not) that the kind of distortion and output level at which it occurs matters as well. It is not uncommon for a Class AB amplifier that measures very low simple harmonic distortion at high power nevertheless sounds terrible at low power where crossover distortion dominates. This is the area where Class A and Class D amplifiers shine . . . while they often measure with slightly higher simple harmonic distortion (which is nevertheless for all practical purposes inaudible at any level) the lack of crossover distortion generally results in a much "cleaner" sound at the low output levels (the "first Watt") more common in home listening.

[Sydney]

Re: Class D Amp Specs

There is also the argument (probably more correct than not) that the kind of distortion and output level at which it occurs matters as well...the low output levels (the "first Watt") more common in home listening.

No disagreement there: Tube amps may not have the lowest HD measurements at the extremes of their performance envelope, but this is less objectionable than non-harmonic distortion. Regardless of how they measure they still provide satifaction for many and "Nirvana" for some.
The top portion of the "envelope" is where the brief peaks occur: That area of power output will be of more signifcance: If a wide crest factor or dynamic range is required and the speakers are not sensitive.

[CUtiger]

Re: Class D Amp Specs

There is also the argument (probably more correct than not) that the kind of distortion and output level at which it occurs matters as well. It is not uncommon for a Class AB amplifier that measures very low simple harmonic distortion at high power nevertheless sounds terrible at low power where crossover distortion dominates. This is the area where Class A and Class D amplifiers shine . . . while they often measure with slightly higher simple harmonic distortion (which is nevertheless for all practical purposes inaudible at any level) the lack of crossover distortion generally results in a much "cleaner" sound at the low output levels (the "first Watt") more common in home listening.

Interesting I was unaware of this but after getting a new amp recently which I believe is based on class D topology(B&O ice module) the first thing I noticed was that it sounded better at lower volumes. I thought it was less noise from the fully balanced upstream signal path but wonder if this has anything to do with it?

At moderate levels the differences are not nearly as noticable.

[Deward Hastings]

Re: Class D Amp Specs

class D topology(B&O ice module) the first thing I noticed was that it sounded better at lower volumes. . . . wonder if this has anything to do with it?

At moderate levels the differences are not nearly as noticable.

I'd venture that it has everything to do with it . . .

[Face]

Re: Class D Amp Specs

Than what does win races

For example, take a car with 350 at the crank, with the stock converter it will have @ 295rwhp and run about run 13.0. Now add a torque converter optimized to the engine's torque curve, in this case say a 3500 stall. It will pull less HP on the dyno, but will run faster down the quarter mile as long as traction still isn't an issue.

[dpasek]

Re: Class D Amp Specs

What is this "torque converter" thing?

Certainly nothing that exists on any automobile worth anything!

It's the coupling between the engine and the planetary gearing for the Turbo Hydramatic 400 that has been very popular for many years in drag racing because it's almost bullet-proof. Those aren't worth anything to some people but worth their weight in gold to others. Depends on your priorities.

[Face]

Re: Class D Amp Specs

It's the coupling between the engine and the planetary gearing for the Turbo Hydramatic 400 that has been very popular for many years in drag racing because it's almost bullet-proof. Those aren't worth anything to some people but worth their weight in gold to others. Depends on your priorities.

Should read, worth their weight in gold to bracket racers.

[dpasek]

Re: Class D Amp Specs

... What I really love are the new DTV final amps. Channel 9's "blockhouse" I've been in. 7.8 megawatts effective output at 0% distortion. ...

Heavy duty stuff, but for how many octaves of bandwidth? .00XX?

Audio systems are really asked to make some extreme performance contortions as compared with the RF domain. Zoom camera lenses have a comparable problem: Try to design a really good 20:1 zoom with imperceptable pincushion, barrel, and chromatic aberration throughout its range, and at reasonably fast apperture. There are ~3:1 fast zooms that are nearly perfect, but beyond that, the compromises start showing.

[dpasek]

Re: Class D Amp Specs

Tube amps may not have the lowest HD measurements at the extremes of their performance envelope, but this is less objectionable than non-harmonic distortion.

Tube amps have a different HD characteristic than solid state amps due to the nature of the devices. Tubes show more even harmonic content, probably due to soft clipping that works more like a compressor than the hard clipping seen with solid state devices. Even harmonics seem more pleasant to the ear while odd harmonics sound harsh. So tube preamps are a popular addition to solid state systems for their second harmonic content.

Some speaker distortions may also not be particularly objectionable, such as the nonlinear responses near the excursion extremes of the voice coils. This is also probably more of a soft clipping situation as long as they don't run into a hard stop.

As for an example of non-harmonic distortion, I have seen only a fleeting mention of intermodulation distortion other than to note that it is quite objectionable.

[dpasek]

Re: Class D Amp Specs

There is also the argument (probably more correct than not) that the kind of distortion and output level at which it occurs matters as well. It is not uncommon for a Class AB amplifier that measures very low simple harmonic distortion at high power nevertheless sounds terrible at low power where crossover distortion dominates. This is the area where Class A and Class D amplifiers shine . . . while they often measure with slightly higher simple harmonic distortion (which is nevertheless for all practical purposes inaudible at any level) the lack of crossover distortion generally results in a much "cleaner" sound at the low output levels (the "first Watt") more common in home listening.

This also seems to be a good argument in favor of bi- or tri-amping following an electronic crossover. Decent class D amps make this architecture very practical. Put this in or near the speaker cabinets and you get the popular powered speakers that also eliminate any frequency response twist caused by wire resistance.

[dpasek]

Re: Class D Amp Specs

Yes, and that's the point - using a number that is unqualified or creating a testing methodology that is not representative of typical operating conditions to obtain desired results.

Yes, indeed. A radar transmitter can have a peak pulse power in the megawatts with an average power only in the hundreds. Peak gives big numbers that superficially sound impressive, but that is not the operating mode for audio except as it relates to transient response.