new hybrid A/D amp

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#3
Class ad audio amplifier - Google Patent Search

It looks like a switching current booster for a standard linear amplifier.
Quite interesting, but keep in mind that the linear stage will have to carry (and dissipate) the whole ripple current of the switching part.
It must be the reason why the linear part has a "switching" cascode implementation.
Possibly the efficiency or maximum swing go down at 20kHz, because the class D part either injects the ripple current to linear amplifier or has a very limited bandwidth.
Another downside is the series sense resistor directly at the output, which limits maximum possible damping factor.

Otherwise it looks like a very nice hybrid in styley cases and lots of functionality.
 
#5
I did simulations with such a topology about 12 years ago. THD looked promising, but pure class-d is still much more interesting. Didn't expect it to be too interesting for being patented (there is even an old patent by some Australins that could probably kill this one here) back then.

Regards

Charles
 
#9
Well ....... let's see:

The main advantage of class-d is its efficiency.
The main advantage of conventional linear amps is that every other performance figure (apart from efficiency) can be made very good with known and easily implemented topologies.

It may thus sound logical to "marry" both of course. But now we will get an amp whose efficiency is still lower than a class-d's efficiency and which is certainly more complicated than either kind of amps alone.

A modern pure class-d amp can achieve the same small-signal- and power- bandwith - something that can't be taken for granted for many conventional linear amps and certainly not for switching/linear hybrids.

Furthermore one has to take into account that class-d is enough mature nowadays to make most conventional amps obsolete. It is only a question of a few years when pure class-d will rival the best conventional amps out there.

Regards

Charles
 
#10
How about 'floating' the ground rail with a class-A amplifier, needing full current capability, but at low voltage (and power-/cooling-) levels. Wouldn't this give class D power and efficiency and simplify/cheapening te class-A amplifier?
 
#11
This idea is feasible and it isn't new either. I don't know whether there is any commercially available product using it however.
You will find quite some info on hybrid amps in AES and IEEE papers.

Nowadays pure class-d is mature enough for not needing bandaids like that. Commercial products are in most cases cost-sensitive. Something like two amps per output doesn't help in this respect.

I have seen measured performance of a new class-d prototype that rivals many conventional amplifiers. I am convinced it will cause quite some hype as soon as it is released to the market.

Regards

Charles
 
#12
This integtated amp has been reviewed in the Hi-Fi News April 2010 issue and got an ecellent verdict. According to the review the analog inputs were not nearly as good as the digital "direct" ones though. There is a brief technical explanation about the function of the amp. For my part I don´t care that much about some specifications as there is very little evidence that the amp that measures the best is the best one. Thus all new (?) ideas are very welcome. I have yet to hear a "pure" class D amp that awakes praise in my mind.

The review in pdf format is here:
http://www.absolutesounds.com/index.php?page=press_view&article_id=367
 
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#13
"Another downside is the series sense resistor directly at the output, which limits maximum possible damping factor."

and

"It may thus sound logical to "marry" both of course. But now we will get an amp whose efficiency is still lower than a class-d's efficiency and which is certainly more complicated than either kind of amps alone."


Read the review in Hi-Fi News. Firstly, the output impeadance is exceptionally low - and the sense resistor is inside the system feedback loop - no need to wory about this. Efficiency of this amp is around 90% . . . . this is as good as leading edge integrated clas s D amps (100-150W).
 
#14
Bonsai said:
"Another downside is the series sense resistor directly at the output, which limits maximum possible damping factor."

and

"It may thus sound logical to "marry" both of course. But now we will get an amp whose efficiency is still lower than a class-d's efficiency and which is certainly more complicated than either kind of amps alone."


Read the review in Hi-Fi News. Firstly, the output impeadance is exceptionally low - and the sense resistor is inside the system feedback loop - no need to wory about this. Efficiency of this amp is around 90% . . . . this is as good as leading edge integrated clas s D amps (100-150W).
Click to expand...

Hi Bonsai,

If you are in Tokyo, the Devialet D-Premier can be heard at the mythic store Dynamic Audio HAL, on the 7th floor among other amps like Goldmund, Behold, etc.
DEVIALET&H.A.L

It was selected for their D300 system (about 3 million yens system) and is in the permanent selection.
 
#15
Hi all,
certainly is a project very professional, very nice especially the section ACD / AD but the end result can be achieved by simply by class D.
ingredients in my opinion and my experience are:
custom drivers, ultra-fast with a particular phase of the DT, this is responsible for defining the sound at high frequencies and thd to load.
this stage should have 25-30ns for "DT" and 30ns maximum propagation delay.
this stage will dissipate about 25W to the mosfet.
Interestingly, DT 25ns to 70ns dynamic realtime controlled by the output current.
after this you may think to develop the rest.
50 ns conversion time and a new scheme for the feedback (no classic) I think that listening can be very similar to class A, AB.
I have developed (for research only) a special class AB with inverse principle of class D. instead of sample, frequency of interruptions are generated proportional to the frequency signal is ingresso.result 75% efficiency, without output filter.
problem is the high cost.🙂


Best Regards
 
#20
I have yet to hear a Class D amplifier that sounds as good as a very good Class AB. The Devialet IMO is ridiculously overpriced and does not interest me. The Primare 132 does not sound as good as my own 120 watt Class AB amplifier and I completely disagree with the Hi-Fi mags reviews on the Primare. I found the Bel Canto S500 to be totally unlistenable. At first switch on it sounded OK but then its unrelenting bright sound made me turn it off , I had to return it to the supplier who loaned it to me. The small size & efficiency of a Class D is very good but IMO these amps are just not musical or organic enough yet. They also appear to have a frequency range restricted to 20kHz
 
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