On Class D Amplifiers Measurements

[ahofer]

" maty said:
Hummm...
If class D has no problem with high frequencies (tweeter), why does KEF use Class AB for the tweeter even in the new €6,000 KEF LS60 wireless? "

Mostly to avoid the hiss in the tweeter.

Good performance in class D for higher frequencies is more expensive (not unattainable at all - see Hypex, Purifi). They needed far less power for the high frequencies and the engineering trade-offs are different for low power/high frequency. It's not some kind of global statement on Class D - far from it.

 

[Mnyb]

Good performance in class D for higher frequencies is more expensive (not unattainable at all - see Hypex, Purifi). They needed far less power for the high frequencies and the engineering trade-offs are different for low power/high frequency. It's not some kind of global statement on Class D - far from it.

It’s also stated it translates to marketing many customers cares about hirez even if we know it’s mostly irrelevant . Many don’t and not many of the shelf class-D amps are built for very extended hf above the audible range ( why should they it’s inaudible ) but never the less if you can stream 24/96 or better some people want the speakers to reproduce the content .

 

[SIY]

Lower power Class D amps don't have the same advantage for efficiency as the high powered ones. So there's less advantage in using one. It will then get down to economics and inventory.

 

[mocenigo]

" maty said:
Hummm...
If class D has no problem with high frequencies (tweeter), why does KEF use Class AB for the tweeter even in the new €6,000 KEF LS60 wireless? "

Mostly to avoid the hiss in the tweeter.

Which hiss in the tweeter? I have a 102Db/W/m AMT tweeter and a 100Db/W/m supertweeter with a class D amp and no hiss even with the ear glued to the drivers. I also asked my 12yo son and he also heard nothing.

Maybe KEF had to choose between a mediocre class D amp and a mediocre class AB one and the latter had less hiss. Mind you, in a commercial active speaker costing 6000€, components must be mediocre to stay in the budget.

 

[antcollinet]

" maty said:
Hummm...
If class D has no problem with high frequencies (tweeter), why does KEF use Class AB for the tweeter even in the new €6,000 KEF LS60 wireless? "

Mostly to avoid the hiss in the tweeter.

I would guess at the low power levels needed for the tweeter, it is cheaper to build class AB than a Class D. No need at all for it to be performance related.

Alternatively, perhaps so they can simply sell a story to clueless audiophiles.

 

[Head_Unit]

no hiss even with the ear glued to the drivers.

Well, but what type of glue did you use? We have to control all the variables in these scientific tests...

 

[valerianf]

I was looking at the Focal Trio 11 Be which is the top of the line of professional monitors.
There is no more class D amp, even for the subwoofer, but a new class G with very low noise floor at low level.
The tweeter is driven with a class AB amp as 25W are sufficient.
In their technical papers Focal clearly said that removing the hiss of the amplifiers was one goal.
The THD+noise of the class G is around 0,05% at 10 mW according to the provided curve.
Is a class D able to do the same for such a low level outputs?
I add that the THD measurements of the class D amps are lower because the BW used for calculation is truncated.

 

[DonH56]

I was looking at the Focal Trio 11 Be which is the top of the line of professional monitors.
There is no more class D amp, even for the subwoofer, but a new class G with very low noise floor at low level.
The tweeter is driven with a class AB amp as 25W are sufficient.
In their technical papers Focal clearly said that removing the hiss of the amplifiers was one goal.
The THD+noise is around 0,05% at 10 mW according to the provided curve.
Is a class D able to do the same for such a low level outputs?
I add that the THD measurements of the class D amps are higher because the BW used for calculation is truncated.

Class AB is often cheaper particularly for lower power level, and at very low power levels control and bias circuits reduce class D's efficiency advantage over other classes. Manufacturers will generally choose the lowest price that meets the design goals.

A look through the review index and searching for amplifiers, e.g. https://www.audiosciencereview.com/forum/index.php?pages/Reviews/ , will show a number of class D amplifiers with THD+N in the -75 to -80 dB range at 20 mW (lowest plotted in the one I checked, a Buckeye Hypex NC502MP design). If it rises to say -70 dB at 10 mW (very conservative extrapolation of the curves) that is 0.032% [100*10^(-70/20)]. As others have said, just look through some of the reviews on ASR.

The "truncated bandwidth" argument has already been addressed in previous posts, not sure it is worth continually repeating that FUD.

I would be leery of using marketing literature as an unbiased technical reference.

 

[Mnyb]

I was looking at the Focal Trio 11 Be which is the top of the line of professional monitors.
There is no more class D amp, even for the subwoofer, but a new class G with very low noise floor at low level.
The tweeter is driven with a class AB amp as 25W are sufficient.
In their technical papers Focal clearly said that removing the hiss of the amplifiers was one goal.
The THD+noise of the class G is around 0,05% at 10 mW according to the provided curve.
Is a class D able to do the same for such a low level outputs?
I add that the THD measurements of the class D amps are lower because the BW used for calculation is truncated.

Class AB is often cheaper particularly for lower power level, and at very low power levels control and bias circuits reduce class D's efficiency advantage over other classes. Manufacturers will generally choose the lowest price that meets the design goals.

A look through the review index and searching for amplifiers, e.g. https://www.audiosciencereview.com/forum/index.php?pages/Reviews/ , will show a number of class D amplifiers with THD+N in the -75 to -80 dB range at 20 mW (lowest plotted in the one I checked, a Buckeye Hypex NC502MP design). If it rises to say -70 dB at 10 mW (very conservative extrapolation of the curves) that is 0.00001% [100*10^(-70/10)]. As others have said, just look through some of the reviews on ASR.

The "truncated bandwidth" argument has already been addressed in previous posts, not sure it is worth continually repeating that FUD.

I would be leery of using marketing literature as an unbiased technical reference.

Yes class-D can do that , but i suspect for a 25w amp the effiency and size gain of class-D migth not amount to much ( as the other poster have cliamed ) . The powersupply is probably still switch mode .

 

[antcollinet]

that is 0.00001% [100*10^(-70/10)].

A small correction if I may:

THD+N is measured as a voltage, not a power, so that should be 100*10^(-70/20) = 0.032%

 

[DonH56]

A small correction if I may:

THD+N is measured as a voltage, not a power, so that should be 100*10^(-70/20) = 0.032%

Duh, brain fart, saw power and calculated as power. Corrected.

Thank you sir!

 

[mocenigo]

Well, but what type of glue did you use? We have to control all the variables in these scientific tests...

Superglue. I want tests to be thorough.

 

[Rick Sykora]

While I really appreciate that some finer points of amplifier specifications are being discussed here (and some other threads), pretty sure we would not be having much of this dialog without Hypex/Purifi supplying the degree of measurements they have.

As for the Class AB comparison, is there a supplier of amplifiers publishing comparable measurements at a price that competes anywhere close to Hypex/Purifi offerings?

 

[LTig]

Superglue. I want tests to be thorough.

If you applied it really close (in the ear canal) it's no wonder you didn' t hear any hiss ...

 

[Rick Sykora]

While I really appreciate that some finer points of amplifier specifications are being discussed here (and some other threads), pretty sure we would not be having much of this dialog without Hypex/Purifi supplying the degree of measurements they have.

As for the Class AB comparison, is there a supplier of amplifiers publishing comparable measurements at a price that competes anywhere close to Hypex/Purifi offerings?

No takers?

Ok, I will add the Outlaw 2220 as I recommended it in another post.

Not much point in an amplifier class war if you have no ammo in your gun!

 

[goryu]

As for the Class AB comparison, is there a supplier of amplifiers publishing comparable measurements at a price that competes anywhere close to Hypex/Purifi offerings?

Is there ANY manufacturer of ANY class of amp that publishes comparable measurements at a price that competes with Hypex/Purifi?

 

[Timcognito]

Is there ANY manufacturer of ANY class of amp that publishes comparable measurements at a price that competes with Hypex/Purifi?

Maybe

Outlaw 2220 Review (Monoblock Amplifier)

This is a review and detailed measurements of the Outlaw 2220 single channel amplifier. It is on kind loan from a member and costs US $399. The look is simple but elegant in its slim form factor. I like that it is just heavy enough to give you confidence but not so much that you can't lift...

www.audiosciencereview.com

 

[Matias]

Is there ANY manufacturer of ANY class of amp that publishes comparable measurements at a price that competes with Hypex/Purifi?

ICEpower, and I think they were pioneers in this level of detailed measurements. This is because they are OEM suppliers to engineers designing amplifiers, just like chip manufacturers also publish detailed datasheets of their products. It just happens that we end customers have access to those and get way more information than what usual amplifier manufacturers disclose to us "lame customers".

 

[goryu]

Maybe

Outlaw 2220 Review (Monoblock Amplifier)

This is a review and detailed measurements of the Outlaw 2220 single channel amplifier. It is on kind loan from a member and costs US $399. The look is simple but elegant in its slim form factor. I like that it is just heavy enough to give you confidence but not so much that you can't lift...

www.audiosciencereview.com

The Hypex/Purifi perform at a level above the outlaw.

 

[goryu]

ICEpower, .

They certainly publish a lot of measurements but not sure about their performance. I haven't kept up with their module revisions.