Class D

"NT"

** Why on earth should it ?? ** No such thing as precise answer to a vague question.

How much do you understand about class B, AB, G or H amplifiers ?

Know much about the issues and drawbacks associated with class D ?

Class D only has one real advantage and often this is not very important.

.... Phil

Except for embedded

--
Dirk

http://www.neopax.com/technomage/ - My new book - Magick and Technology

And portable very high power PA with some kW

Marte

"Marte Schwarz"

** Not even there.

AC power is plentiful and the advantage in efficiency is marginal over class H or G.

More useful is to have an active PFC corrected PSU in every amp.

.... Phil

Very briefly: B: unbiased output devices, crossover distortion an issue. Efficiency better than AB

AB: biased slightly on, no crossover distortion, but less efficient. Most widespread audio amp topology.

G: Switched psu rails. More efficient but added psu costs

H: Tracking psu rails. Even more efficient but more psu cost.

AIUI Class D has the following advantages

1. Power efficiency. usually not very important in engineering terms for audio amps
2. Less heat generated means more compact and/or cooler equipment, less heatsink metal, less battery drain.
3. Smaller cheaper psu.

But also disadvantages of

1. Higher upfront cost, both BOM and design time, for amp + psu
2. Generation of spurious audio frequencies
3. RFI

So, the core of my question is are there other downsides to D?

NT

Audio performance of most Class D audio amps are not as good for full range use. Most class D amps on the market now are for low frequency operation. Can a class D be designed for good high frequency performance, yes, but they just don't tend to since in music, the high power consumers are the subwoofers.

As for the golden ears....They have a hissy about Class AB switching between two transistors as opposed to a Class A... Lets not even talk about tubes.

Now of you brought a Class D tube amp to the market...lookout. :)

nt.

ge

ion.

hey

So, if I'm understanding and extrapolating correctly, the extra costs of D (control circuitry, inductors, design time) aren't justified at low & medium powers.

... which leaves class AB squarely in the frame as the audio amp of choice for 98% of cases.

een

.

hmmm :)

NT

"NT" "Phil Allison"

Very briefly: B: unbiased output devices, crossover distortion an issue. Efficiency better than AB

AB: biased slightly on, no crossover distortion, but less efficient. Most widespread audio amp topology.

G: Switched psu rails. More efficient but added psu costs

H: Tracking psu rails. Even more efficient but more psu cost.

AIUI Class D has the following advantages

1. Power efficiency. usually not very important in engineering terms for audio amps
2. Less heat generated means more compact and/or cooler equipment, less heatsink metal, less battery drain.
3. Smaller cheaper psu.

But also disadvantages of

1. Higher upfront cost, both BOM and design time, for amp + psu
2. Generation of spurious audio frequencies
3. RFI

So, the core of my question is are there other downsides to D?

** You are too dumb too see the nose in front of your face.

There is no good reason why class D should be ubiquitous - and so it is not.

.... Phil

I have designed both class AB and class D and they sound pretty much the same across the audio band.

I dont know who started the rumours about class d only being good for bass but it is totally untrue.

"Roger_the_Dodger"

** The best class D audio power amps have near equal performance to the best class AB designs and no audible issues.

Only a tiny few makers have been successful a producing reliable, high powered class D amps - notably Crown Audio in the USA and Powersoft in Italy.

The Crown K series amps ( released in about 1996, now deleted) showed how it could be done.

The topologies used by Crown and Powersoft are covered by patents, which seem to have prevented others following suit.

.... Phil

t.

s

On occasion you say something sensible and constructive, but I guess not today.

NT

"NT" "Phil Allison"

On occasion you say something sensible and constructive, but I guess not today.

** Fuck off - you tenth witted, stinking damn troll.

Subwoofers and other bass loudspeakers are currently built using very small boxes, requiring speaker elements with low efficiency and thus high drive power, compared to old 3-30 W tube driven systems with large boxes. In subwoofers the class D switching frequency can be quite low, thus allowing slower, more robust switching transistors to be used. It might be a good idea to move the switching frequency just above the audio range, say 25 kHz, to avoid any possible switching frequency break through and also simplifying the output low pass filter design (the slope can be several octaves long).

A full range class D amplifier would require a switching frequency in the 250-500 kHz range, needing faster transistors and steep output filtering.

IMHO, the higher octaves are best served by linear amplification stages.

I still do not understand why anyone are still building loudspeaker boxes with passive crossover, good quality inductors and bipolar capacitors are expensive compared to the cost of current power amplifiers. The amplifiers driving different elements could be better tailored for the frequency range and power range needed.

A 1-50 kW AM transmitter followed by a full wave rectifier ?

On a sunny day (Wed, 27 Jul 2011 10:47:53 +1000) it happened "Phil Allison" wrote in :

Phil, a question. Sometime ago there was a discussion on that Philips (IIRC) patent that used a very simple circuit to make class D audio. Think it was called UcD, and at that time I found several very small modules for sale on the web.

What do you think of that?

"Jan Panteltje" "Phil Allison"

** Post all questions to the NG.

** Send me one so I can bench test it.

I have already done this with a Crown K series and several Powersoft amps.

They were both staggeringly impressive.

The Crown K2, because without being told I would not have been able to pick by testing alone it was a class D design at all.

The Powersofts, because they were of 1 rack unit size and produced circa 3.2 kW of audio power at low THD ( 0.05%) and with pure sine wave mains current draw.

.... Phil

Indeed! I was using bi-amps and active filters ~35 years ago.

...Jim Thompson

[On the Road, in New York]

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I love to cook with wine.     Sometimes I even put it in the food.

lol. Love ya Phil Doesnt life feel enjoyable when youre like that.

Hi snipped-for-privacy@downunder.com,

(very unusable name here in Europe ;-)

I don't see any reason why anyone should do this. 50 kHz should be enough for all. The filter charakteristik above all frequencies anyone can hear should also not be any problem. Shure you can measure the differences in the signal but who cares, nobody would hear the differences.

Marte

"Marte Schwarz"

** Then you are a fool.

** How did you get that silly idea ??????

PWM is not the same as Nyquist sampling.

All high performance PWM amplifiers use 250 kHz of higher switching.

So they all use MOSFETS.

..... Phil