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In Reply to: RE: I usually am not in favor of active loudspeakers... posted by John Marks on July 24, 2024 at 09:29:17
Hypex Class D amps (nor most for that matter) are NOT "digital" amps.
Switchers, yes but they operate in the analog domain. Let Bruno Putzeys 'splain it to you...
Follow Ups:
I think the term (digital) come from the way the output is generated. These are a PWM or pulse width modulator where the output is not linear like A or AB, B but a switch closure between a high or low power supply voltage.
IF that switch is very fast but is only "on" 10% of the time, the power delivered is 10% of what would be possible if the load were connected directly to the power supply.
The up side is unlike a linear output where the device dissipation is the current times the voltage across it, the switch is either on or off, neither condition dissipates much energy.
The trick is, the switching frequency has to be much higher than the highest audio frequency in question, typically at several hundred KHz.
The higher the switch frequency, the easier it is to make the low pass filter that turns this into analogue and then, the easier it is to "close the loop" around the output.
There is nothing handled in the digital domain with any of Bruno Putzeys class D designs - UCD, Hypex, Mola Mola or Purifi. Switch mode amps are inherently analog in their operation just like John Ulrick's Infinity SWAMP amp introduced in the 1970s. Hypex amps have analog inputs and analog outputs.Just ask him .
A class-D power stage," Putzeys wrote in an email, "just like a class-A power stage, produces distortion that depends on the power supply and on the output current that the speaker draws." Engineers deal with that distortion via what Putzeys called "highly analog countermeasures." If a problem has an analog solution, then it must be an analog problem. Besides, you can't make a loudspeaker's cone move with code."
Remember this from the link found in the previous post?
Such, however, does exist with products like the NAD M2 "Direct Digital" amp which contains a DAC to do initial conversion for analog inputs to the digital domain.
Edits: 07/25/24
I never said anything was in the digital domain, i explained how the output signal is produced internally and HOW one could think it was digital.
The process is called a pulse width modulator and is based on an electronic "switch closure" and it's duty cycle. I designed several of these in the past for servomotor driven subwoofers and a 100 amp regulator that flew in the shuttle. See if the description makes sense including closing the loop with negative feedback
sounds like but isn't.
Agreed, all class D amps are analog. Class D is an analog format. It's unfortunate that it's called class D especially since the signal is encoded and decoded but it is an analog encoding. The combination of encoding and the name class D makes people who don't understand the format assume D is for digital since we live in a digital universe these days.
The reason it's called class D is simple. There were 3 formats defined previously. They were A, B, C(decidedly not an audiophile format). And the fourth format was D since D comes after C.
similarly folks often assume the wrong answer to the prefix found on Armalite products. It represents the company name.
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