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Audiophiles, generally don't like class D amps!

DanielT

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I’ll wait until we have class-F amplifiers for audio and see what the religious makes up about that :D
Heh heh. :)

Incidentally, about class D and arguments from certain audiophiles, I, and probably many others, have heard (the usual?) arguments such as the classic that it sounds sharp and hard, for example. Hardcore audiophiles prefer distortion factories in the form of single end 300B tube amps that may have a maximum power of two watts. Preferably then a ditto amp with a price tag upwards of $10,000.

There are many strange things I have heard being said. Example this at a HiFi fair (obviously by a class D hating audiophile): "The negative feedback in that amplifier created a too quiet sound, an abysmal black hole, in the quiet parts of the music. A spooky sound."
I went and had a sandwich and coffee instead of engaging in that discussion.

Do not put any of these types of audiophiles in a blind test. They will always come up with an explanation as to why they heard no difference. If DACs and or amps are tested, it will be said that of course you hear no differences with those speakers. Or that they are having a bad day and couldn't concentrate on hearing differences (that they obviously always hear otherwise), and so on.
 

voodooless

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There should be some information theory that applies to this, separating the binary "on off" from the values, but I can't remember the terminology used.
It’s a coding scheme, or codec if you like.
 
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mhardy6647

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I’ll wait until we have class-F amplifiers for audio and see what the religious makes up about that :D
I don't think that Class F amplifiers have any audio-band applications -- but I speak with zero authority on the matter. :oops:

Now -- Classes G and H. BTDT, as they say. A couple of different but related schemes to improve (average) electrical efficiency in a push-pull amplifier.

Class G:

(from a Hitachi brochure, ca. 1977)

Class H: Originally called "Vari-proportional" by Soundscraftsmen :)

1707228247026.png

source: https://www.worldradiohistory.com/A...iFI-Stereo/70s/HiFi-Stereo-Review-1977-10.pdf

1707227415384.png

source: https://www.worldradiohistory.com/A...e-High-Fidelity/80s/High-Fidelity-1981-11.pdf

Later upgraded to "A Class of its Own" ;)

1707227877248.png


source: https://www.worldradiohistory.com/A...e-High-Fidelity/80s/High-Fidelity-1981-08.pdf
 

mhardy6647

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AdrianusG

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I don't think that Class F amplifiers have any audio-band applications -- but I speak with zero authority on the matter. :oops:

Now -- Classes G and H. BTDT, as they say. A couple of different but related schemes to improve (average) electrical efficiency in a push-pull amplifier.

Class G:

(from a Hitachi brochure, ca. 1977)

Class H: Originally called "Vari-proportional" by Soundscraftsmen :)

View attachment 347771
source: https://www.worldradiohistory.com/A...iFI-Stereo/70s/HiFi-Stereo-Review-1977-10.pdf

View attachment 347766
source: https://www.worldradiohistory.com/A...e-High-Fidelity/80s/High-Fidelity-1981-11.pdf

Later upgraded to "A Class of its Own" ;)

View attachment 347769

source: https://www.worldradiohistory.com/A...e-High-Fidelity/80s/High-Fidelity-1981-08.pdf
Wow, that Hitachi:)
don't know this one or that it was any good, but it sure looks fantastic.
I love that age of Big Bold Receivers.
 

mhardy6647

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Wow, that Hitachi:)
don't know this one or that it was any good, but it sure looks fantastic.
I love that age of Big Bold Receivers.
The big receivers of that era suffered the same fundamental design "issue" that plagues many modern big AVRs -- too much stuff in one box/sharing one power supply: Too much heat, and too much to go wrong. The era of proprietary electronic components was looming by then, too (i.e., repairability was already waning). But, yeah, impressive -- not to mention large, heavy, and expensive. ;)

In fairness, Hitachi here was trying to give more amp with less heat, but given the grip that "FTC" power specsmanship had on the consumer mentality in those days, I think many folks back then drew the opposite conclusion from Class G amplification: This was a 200 watt amp that pretended to be a 400 watt amp (but wasn't)! In fact, in the real world, there's probably much to be said for the Class G and H approaches for high-powered push-pull amplifiers.

All that being "said" (written): Class D would have helped a lot with those monstrosities, in fact (and on topic)! ;)
 

DonH56

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Here is my very old post on amplifier classes. Crown's class I and TriPath's class T are not part of any standards AFAIK (but not something I follow closely) but rather are variations of class D (using interleaved switches and such). I do not see classes E or F used in audio; they are narrow-band tuned topologies used for RF/mW circuits AFAIK.

Amplifier Classes

Here is a summary from memory so don't hold me to any mistakes:

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% (SE) to ~78% (push-pull) 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.

There are some more esoteric classes I am not familiar with. I have only designed and worked with the classes above.

HTH - Don
 
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atmasphere

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I hope we can put this class D vs digital thing to bed. Both are switching technologies. Class D is an entirely analog process though. You can have a digital front end if you like but you will have to do a conversion to the analog means that the class D analog section is using.

Class D was first proposed in the 1950s when tubes were king and the first home class D amps were sold by Sinclair in the 1960s. The fact that the D is there is simply because A, B and C were taken and nothing more. A confusing coincidence...
 

mhardy6647

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Did not sony built a pwm amp in the 70's ?
I wouldn't be surprised!
Let's look...

By crikey, they did indeed! :)
1707248648932.png


1707248883309.png


A quick search of WRH.com didn't turn up any test or review of it. :(

You know... It's too bad that bronze finish didn't become more popular for domestic hifi. I rather like it! ;)

EDIT: A few specs from 1981'a Stereo Review Equipment Directory.

1707249351641.png


source: https://www.worldradiohistory.com/A...ive-HiFI-Stereo/80s/Stereo-Directory-1981.pdf
 
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Ze Frog

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I don't consider myself an 'audiophile', anyone who uses that moniker is usually rather pretentious and a bit of a knob. I do really appreciate music and Hi-fi gear though and personally I think class D is absolutely perfect.
 

Chrispy

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So much nonsense about audiophools not understanding their gear (like that's new).
 

Mnyb

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So much nonsense about audiophools not understanding their gear (like that's new).
The tech hobby where almost exclusively all participants are tech ignoramuses' ? This lead to the cargo cult mindset of admiring a large power suplies or fancy brand name capacitors :)

Ohm law are beyond most of the audiophiles ( U=I*R , P=I*U ) as we get these weird power and impedance questions on weekly basis ?

Combine that with the latest bad turn in peoples mindset the last decades , never trust experts because they are in some secret cosnpiracy ( like climate change ;) )

So they believe Paul or a random youtuber instead ? The combination is toxic .

The dawn of social media and the BS asymmetry principle ( Brandolinis law ) will eventually doom all real knowledge :(
 

Ze Frog

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The tech hobby where almost exclusively all participants are tech ignoramuses' ? This lead to the cargo cult mindset of admiring a large power suplies or fancy brand name capacitors :)

Ohm law are beyond most of the audiophiles ( U=I*R , P=I*U ) as we get these weird power and impedance questions on weekly basis ?

Combine that with the latest bad turn in peoples mindset the last decades , never trust experts because they are in some secret cosnpiracy ( like climate change ;) )

So they believe Paul or a random youtuber instead ? The combination is toxic .

The dawn of social media and the BS asymmetry principle ( Brandolinis law ) will eventually doom all real knowledge :(
So true, humankind isn't really intelligent enough for the technology we possess, and people can be very highly educated but still a total plank. The internet should have been the gift of knowledge, and to some point it once was. It still is, to a point, but everyday things deteriorate even more.

It's my kids I worry for, although I teach them to never trust a first source and never only seek an opinion that matches their own. YouTube is a prime example, my youngest loves science, but I have to teach him to navigate around the fake science that plagues YouTube now. YouTube though has become a tool for various parties in this world now, some nefarious and others just people craving attention. I'm amazed at the scam ad's lately, it's of epidemic proportions. Lol, seriously, if I hear about that bloody home security camera again...'made by 2 UK engineers', cuts straight to a Chinese woman in a factory in China. ROFL, but I bet seemingly smart people fall for this stuff, otherwise how do they afford to spam every single video with the adverts.
 
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Nice YouTube demo here between two premium Class AB and Class D amps. If your setup or headphones are resolving enough, there are subtle differences that can be heard.
 
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