class D vs. class X

[Haunz 10+ year member]

the key seems to be the power supply. Without further knowledge, its uncertain what they mean by "digitally controlled" power supply. no mention is made of what the controller's goal is. Plenty of amps do use regulated power supplies for consistant performance. JL uses one to allow a wide range of speakers to be used equally well. Class G/H amplifiers use one to improve efficiency. Class D itself has a few variations to improve efficiency or accuracy as well.
my best guesses are that the supply is regulated* just like other class D amps. it may adjust itself as a class H amp would. this would bring about an increase in efficiency as switching losses would scale with the output level. but again, thats just a guess.

* keep in mind the "same power at any load" part of JL's RIPS is the I, not the R...

That is a negatory...

the PSU is loosly regulated, and the rail voltage does not swing with the input signal as it would with a class H design...

Its just a run of the mill class D amplifier...

 

[pawn man 10+ year member]

from what i understand the x class is a type of digital class amp. most d class amp are only 75% - 95% eff. i have also heard that the hk4000 were current hogs.

 

[dcole18 5,000+ posts]

20 bucks will get you the answer

 

[Enellz 10+ year member]

Class X is not a recognized class of amplifier design. Sounds like the creation of the marketing department.

BINGO! LIES, I tell you, ALL LIES!

 

[helotaxi 5,000+ posts]

from what i understand the x class is a type of digital class amp.

No such thing as a digital amp. Switchmode, sure. Digitally controlled, possibly (though the amp in question I can pretty much guarantee isn't) But a digital amp? Not possible. Digital would mean 1's and 0's and those are what they are, you can't make a 1 louder.

most d class amp are only 75% - 95% eff.

Only? That's funny. Especially when compared to Class A/B which might muster 70% at full power and get less efficient at lower power levels.

Curious as to what you would gain by varying the rail voltages on a Class D amp. I understand the benefit with a Class A/B and especially a Class A but why would you bother with an already almost perfectly efficient design?

 

[pawn man 10+ year member]

jmdc said d class amps were 100 % eff. i know ab class amps are not as eff. as d class amps. a lot of manufacturers call d class amps digital amps.

 

[Ed Lester 10+ year member]

How about Digital Op amps?

I have built them.

 

[helotaxi 5,000+ posts]

An Op amp is not a power amplifier.

 

[Haunz 10+ year member]

Curious as to what you would gain by varying the rail voltages on a Class D amp. I understand the benefit with a Class A/B and especially a Class A but why would you bother with an already almost perfectly efficient design?

I don't know of any class D amps that use a signal tracking power supply.. but I wouldn't be surprised if someone makes one...

class Ds are typically very efficient at full swing, but at lower output levels you will find efficiencies closer to 60%-70%. Infact, a class D amp is least efficient when it's not producing any power at all. This is because the outputs are still being switched, and that generates considerable losses. For that reason having a rail voltage that tracks the signal could significantly increase the amplifiers overall efficiency.

Class BD amplifiers address this problem in a different way and have an output stage that operates with a zero pulse width when no input signal is present...

 

[helotaxi 5,000+ posts]

^^^That does not at all fit my understanding of how a Class D amp works. The biggest plus of the Class D design is that it is just as efficient at partial power as it is at full power for the simple reason that you are never using any of the output devices in a partial on state. They are either on all the way off. If there is no signal the output devices should not be switching at all. They should be all off. That would leave you with the idle current running the power supply switching, but all amps have that.

 

[thch 10+ year member]

class D is a pretty loose class for amplifiers. this sounds a bit like multi-level class D, with 3 levels - 0V, +V, and -V.

normal class D is always switching, between +V and -V. and to output 0V, it just switches to +V for half of the time, -V for the other half. with the high-frequency switching removed, only the 0V average is left. But this does consume a small amount of power.*

* in practical applications. ignoring parasitics allows for 100% efficiency.

 

[helotaxi 5,000+ posts]

That would pretty much be the idle current, correct? At zero power all amps still draw some power and all run at a whole 0% efficiency.

 

[audioarsonal 10+ year member]

The hk4000d pulls like 4-5 amps just turning it on.

 

[Haunz 10+ year member]

That does not at all fit my understanding of how a Class D amp works. The biggest plus of the Class D design is that it is just as efficient at partial power as it is at full power for the simple reason that you are never using any of the output devices in a partial on state. They are either on all the way off. If there is no signal the output devices should not be switching at all. They should be all off. That would leave you with the idle current running the power supply switching, but all amps have that. .

That would pretty much be the idle current, correct? At zero power all amps still draw some power and all run at a whole 0% efficiency.

If you understood how a class D amp works, it would be clear why idel current draw is typically higher then it is for an A/B class amp... not to mention why they are less efficient below full power output levels...

As I said, at full boar a really good class D amplifier can boast efficiencies approaching 95%.. but at levels which approximate the duty cycle of music few exceed 75%...

 

[helotaxi 5,000+ posts]

Assuming that is true, you probably know more about the specifics I just know the basic theory, it's still a far cry more efficient than a Class A/B which runs around 30% under normal use and a Class A is at best a 25% at any power level.