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When did class D start to not suck?

fpitas

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Tangband

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Anybody who has been reading/watching hifi reviews is highly likely to have seen or heard the regurgitated comment that “class D sucked way back, but is now good.” Sure.

My question is; when did it start not to suck? Who made the module?

Just curious if there is a known delimiter out there.
If you look at one of the many Genelec investigations and white papers, their conclusion from 2013 showed that the tecnique were good enough that year.

 

Jim Shaw

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Forgive a little arrogance here, but reading this thread is one fine example of "monkeys and footballs."
Or, as ranchers are wont to say, "All hat and no horse."

Digital amplifiers have as few similarities to analog amps as mammals and reptiles share in the animal world. That they provide power, current and voltage to speakers is about the totality of similarity. The topology, mathematics, circuit devices, and design techniques are almost completely different. Transfer functions between stages and at nodes are hardly comparable. Don't think E=I*R; think s transforms, transfer functions, filters, rise times, and switching rates.

This is why old line circuit designers of tube and transistor analog systems (not to mention old line music listeners) have found it so difficult to transition. Yet, measurement technology at the listening output remains mostly similar. You don't have to trade in your ears or musical tastes. But you do have to give up your fantasy that you still know what's really going on inside. The core information theory and mathematics are all different from analog, both solid state and vacuum tube. Otherwise, you can end up thinking like Darko, that digital is simply analog in disguise; it isn't. And avoid covering your alibis with acronyms. That's more like describing the whole animal kingdom by counting their toes.

But don't listen to me. Listen to the fellows who taught me information transfer, modulation, and noise a few decades ago. The textbooks are out there. Since then, it's been all about new techniques, switching times, purpose-designed devices, and better filters.

[I already regret writing this.] :)
 

fpitas

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ZolaIII

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Why do I need the rest? You claim Hypex amps are class DG, so I ask why you think that is.. If I understood that wrong, enlighten me.
It doesn't matter if it's DG or DH (but you know that by now for sure) they (in the official documentation) described it as class D with H bridge which you surely remember as you mocked to it earlier.
H-bridge != Class H :facepalm:
Fell free to ask them.
I showed what whose a turning point, indicated when it happened, showed it's not tied to A, AB or ABC typology directly, showed how it's tied to class D also, told you easiest way to recognise it in any design. I think that's plenty from me. In the mean time you had a good time probably, mocking at me but that's only achievement you maid.
Have a plesent evening and bother somewhe else who cares.
 

voodooless

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It doesn't matter if it's DG or DH (but you know that by now for sure) they (in the official documentation) described it as class D with H bridge which you surely remember as you mocked to it earlier.
Oh, now it doesn’t matter? This is getting better by the minute :facepalm: The H-bridge is not in dispute here, calling it class H is!
Fell free to ask them.
No need, all over the internet there are plenty of sources showing us what a class H amplifier is, and it’s not an amplifier with an H-bridge. Many others have explained as much. You seem to be quite alone with your reasoning. Otherwise @boXem | audio can be probably a stand-in for Hypex (if he dares ;) ), since he designs and sells the damn things ;)
 
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ZolaIII

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Oh, now it doesn’t matter? This is getting better by the minute :facepalm: The H-bridge is not in dispute here, calling it class H is!

No need, all over the internet there are plenty of sources showing us what a class H amplifier is, and it’s not an amplifier with an H-bridge. Many others have explained as much. You seem to be quite alone with your reasoning. Otherwise @boXem | audio can be probably a stand-in for Hypex (if he dares ;) ), since he designs and sells the damn things ;)
For the rest ask them directly!
Including why it specifically needs one of those.
 

dfuller

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Class A = bias current flows through the output devices all of the time. Most wasted energy and heat, max theoretical efficiency ~50% for a push-pull design (only ~27% for a single-ended design IIRC). Commonly used for low-level circuits like preamps and power amp input and driver stages, rarely for output stages since it is so inefficient. More common in tube amps these days, I think.

Class B = bias current flows half the time, so in a push-pull design one device is on and the other is off. Typically one device amplifies the (+) half of the signal and the other the (-) half as it swings around ground (0 V, or a common bias voltage). Can achieve ~67% efficiency in theory. In practice there is crossover distortion around the crossing point as one device is switched off and the other turned on since it does not happen instantaneously. Used for some power amplifiers in the past (do not know about today), with feedback used to reduce crossover (and other) distortion.

Class AB = biased in class A for small signals then moves to class B. This lets small signals around the crossing point stay in class A for lower distortion, then as the signal increases and moves out of the small signal region transitions to class B to save power.

Class C = bias current flows less than half the waveform cycle. The "missing" energy is usually generated by a resonant circuit (e.g. inductor/capacitor (LC) tank). Common in RF circuits where high power is needed and distortion less an issue, and oscillators which are narrow-band (audio is very wideband, spanning multiple decades) and incorporate a resonant circuit by design.

Class D = bias current flows only as output devices switch states, in a form of pulse modulation (pulse width, frequency, or both). Can achieve >90% efficiency. The high switching frequency is provided by a clock source or (for most audio amps) is self-generated by the circuit. The output pulse train is filtered so only the fundamental signal remains. See https://www.audiosciencereview.com/forum/index.php?threads/class-d-amplifiers-101.7355/

Class E, F = utilize switching as well but constrain the switching to certain points in the signal cycle (e.g. at voltage or current zero crossings) for higher efficiency since less power is dissipated in the switching transistors. These are used exclusively in RF circuits AFAIK. Class E is used in tuned amplifiers (narrowband, again) and class F is used for generating harmonics of the fundamental so you can say build a high-frequency oscillator output from a lower-frequency circuit.

Class G, H = wrap a varying power supply around the core (typically AB) amplifier to improve efficiency. By changing the power supply voltages it uses (wastes) less energy for small signals by applying low supply voltage, then increases the voltage as required as the signal gets larger. Class G uses discrete rails so the power supply switches between two or more (high/low) voltages. Class H uses a tracking supply that varies continuously with the signal level.
Close, Class B can do 78% efficiency theoretically. A lot of those little battery powered transistor radios were Class B.

As for Class AB - better to think of it more as "Class B, but with a small idle current to remove crossover distortion" IMO - they've been standard power amps for ages (80+ years) for a reason.

C, E, F yeah all RF amplifiers. Distortion doesn't matter - just use a tuned circuit.

Class D resembles the primary side of a SMPS rather closely, wouldn't you say?
 

Chrispy

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You said: ‘Did you take a Rip Van Winkle type nap or something?’

maybe you need a nap yourself, you are starting to sound a bit grumphy :)
Moi? It's not exactly a new thing otoh....
 

Doodski

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Class D resembles the primary side of a SMPS rather closely, wouldn't you say?
At some level it is similar. I still wish we could see the schematic of a leading model or three of class D amplification with power supply attached or not.
 

restorer-john

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At some level it is similar. I still wish we could see the schematic of a leading model or three of class D amplification with power supply attached or not.

Go download the NAD M22 service manual.

Full schematic of their bespoke SMPS and full NC-400 OEM Hypex schematic.
 

Adam Bernau

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Probably before you were born. 1976.

Sony TAN-88:
View attachment 225489

Yes, thats a SMPS and yes, they're VFETs in a Class D design. Yes, it's a die-cast block of alloy making up the chassis. It weighed only 11kg, put out well over 160wpc@8R, S/N over 110dB, distortion curve flat from 10W to nearly 180W.

Bruno Putzeys was only three (3) years old when it was sold.
Nice! I have missed that one! <3
I think that the amplifier modules that sir Clive Sinclair produced as one of his first inventions (since 1963) were also Class D btw
 

Doodski

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Lots of techy literature there for sure. The exploded view of the PCB mounting is as usual a PCB sandwich from what I can see.
zzzzzzz m22 1.png

zzzzzzzzzz m22 2.png
 

posvibes

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That isn't really a class of amp as such, it's a trademark by Tripath who made class d chip amps which were used in various consumer devices.
That Sonic Impact tripath amp has become and was legendary, I remember reading the 6moons review and being totally intrigued and thoroughly impressed I got one as quick as I could. Subjectively I though it was the best amp I ever used on my Maggie SMG's, I know, I know, but damn it, it was!
 

DonH56

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Close, Class B can do 78% efficiency theoretically. A lot of those little battery powered transistor radios were Class B.
Yes, duh, thanks for the correction. When I first had to derive the efficiency equations it was all single-ended stuff, and I keep having that in mind. I agree, ~78% or so for push-pull B designs, that sounds right. My bad; I need to correct my old post. I had already updated the class A efficiency number but overlooked class B.

McIntosh is the one I remember for their big class B audio amps "back in the day".

As for Class AB - better to think of it more as "Class B, but with a small idle current to remove crossover distortion" IMO - they've been standard power amps for ages (80+ years) for a reason.
Some are pretty heavily biased into class A, but the trend is away from that. I also didn't mention things like Benchmark's AHB2 using feedforward (FF) compensation to clean up the output. I played around a lot with FF designs but in the pulse world of radar it was a mixed bag -- much faster pulse response, but tended to overshoot and long settlers (sort of like doublets in feedback amps, but different cause).

C, E, F yeah all RF amplifiers. Distortion doesn't matter - just use a tuned circuit.
Well, it matters a little, but the resonators filter much (hopefully most) of it away. Fine if you don't need a wideband amp.

Class D resembles the primary side of a SMPS rather closely, wouldn't you say?
Others have made that observation as well and I tend to agree. That said, while I've some experience with them, I do not claim to be an amplifier designer, certainly not audio amps. Did a few, mostly they worked...
 

RammisFrammis

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Probably before you were born. 1976.

Sony TAN-88:
View attachment 225489

Yes, thats a SMPS and yes, they're VFETs in a Class D design. Yes, it's a die-cast block of alloy making up the chassis. It weighed only 11kg, put out well over 160wpc@8R, S/N over 110dB, distortion curve flat from 10W to nearly 180W.

Bruno Putzeys was only three (3) years old when it was sold.
I bet the cast metal chassis was to keep shrapnel from injuring people when the electronics exploded. Looks very version 0.89 to me. :eek:
 

DonH56

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I bet the cast metal chassis was to keep shrapnel from injuring people when the electronics exploded. Looks very version 0.89 to me. :eek:
It was actually a pretty great amp and quite reliable, unlike some other amps of that or this day. IIRC it had better output protection than most other amps. You want shrapnel, look no further than the late great Blaze Linear 700 I owned that self-destructed several times, even driving a fairly benign load (Maggies).
 
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