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New world of HiFi with Chinese Class D Amps.

P.M.B.66 said:
That forum is full of hearing impaired morons that can't even hear the difference between Op Amps and only rely on numbers and misinformation in this cult forum. Sorry. Wouldn't waste my time. Give them few truths and they lose their s*** and can't debate like adults turning to personal insults. Unfortunately this audiophile hobby has many that can't hear and then turn to argue with people that can.
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Yeah. Let's leave setting the tone for an informed, civil discussion to us enlightened folks huh.
 
P.M.B.66 said:
There was no discussion about surround sound. Plus too much challenge again got me banned even that I provided references to back it up. All I got after that was requests to put it in different wording, nit-picking and disrespect that I dished back or ignored. Yeah that forum is a cult with mislead minions mostly. Not sad as it was expected that the admin couldn't handle the truth.
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But if you are talking about surround sound the effect has to come from the Audio Visual Receiver itself plus the original source to create the surround sound effect (DVD/Blue Ray usually). That's another point why AVR is not the best for Bi Amping and doesn't work. We are still talking about 2.0/2.1 systems. So taking front signal and rear signal that are different and asking the speaker to do two different things simultaneously won't have a good result. That should be logical.

But two separate Stereo Amps with volume knob the same signal Left and Right used to power the High and Low separate you get more power and the control between the woofers and Tweeters separate by controlling the power. Crossover balances the power between High and Low but by powering the High and Low separate you now have the control. You controlling the power between high and Low the crossover loses lot of it intended function. Yes it is still there but not doing much.

If you ask a question from Google you get fairly good answer. "Benefits of passive amping?

Passive bi-amping provides several potential benefits, primarily by delivering more power and control to speakers that have separate inputs for high and low frequencies.
Crutchfield +1
The main benefits include:
  • Increased Power and Headroom: By using a separate amplifier channel for each speaker section (woofer and tweeter), you are effectively providing more total power to each driver. This results in greater dynamic range and more headroom, which can lead to a cleaner and fuller sound, especially during demanding musical passages.
  • Better Driver Control and Tighter Bass: The extra power dedicated to the low-frequency driver can result in tighter, more controlled bass response and more impactful low notes.
  • Reduced Intermodulation Distortion: By separating the amplification for different frequency ranges, the low-frequency signals are less likely to modulate or interfere with the high-frequency signals, which helps to reduce distortion and "muddy" sound.
  • Improved Clarity and Soundstage: Many listeners report increased clarity, better definition, and a wider, more open soundstage, as the separation of signals allows for a more accurate placement of instruments within the stereo image.
  • Easier Load for Amplifiers: The speaker presents a less complex and "easier" electrical load to each amplifier because each amp only has to deal with a limited frequency band. This can reduce stress on the amplifiers.
  • Cost-Effective Upgrade Path: If you already own a compatible receiver or a second amplifier, passive bi-amping can be a relatively inexpensive way to improve sound quality compared to upgrading the main amplifier or moving to a more complex active system with external crossovers.
Ultimately, the perceived benefits can vary depending on your specific equipment and listening environment, but many audiophiles find it to be a worthwhile improvement.
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Op Amps we have been talking about Class D Amps all along where the circuitry is simple. If we were talking about expensive A/AB Amps with over the top complicated circuitries you would be right the audible difference would be minimal and you most likely wouldn't hear the difference. But Class D is very simple where changing something small can make a huge difference to bad or worse or brilliance. That's why there are popping new vendors selling specially made Op Amps that can cost as much as the Amp itself. Yes there is a big difference. But here is the catch that gets halve of the audiophiles nickers in a knot. Their hearing is not good enough. These people only rely on numbers because their hearing is poor and now we are back into the circuitry design where you can and can't. I personally don't claim to have a super human hearing but it is good enough to spot differences even on youtube blind tests. Of course not all because some just are very very poor quality and some Op Amps are so close that it is more of a guess from a gut feeling. But if you would ask to spot differences between ne5532, opa1612 or Sparkos Op Amps you should be able to hear it with a good difference even on moderate youtube comparison.

Again ask a question. "why different Op amps sound different on Class D amps and not on class A/AB amps?"

Op-amps in Class D amps have a higher impact on sound because they operate within the critical, high-gain feedback loop that shapes the pulse-width modulation (PWM) and manages output filter interaction, whereas in Class A/AB amps, they often only act as pre-gain stages with less impact on the final output.
YouTube +1
Key Reasons for the Difference:
  • Feedback Loop Sensitivity: In many Class D designs, the input op-amp is directly involved in the feedback loop that controls the switching mechanism. A different op-amp changes the loop gain and speed, significantly affecting the reconstruction of the audio signal.
  • Interaction with Output Filter: Class D amps use an output inductor/capacitor filter. The op-amp's characteristics influence how the amplifier handles the impedance load of the speaker, which can lead to high-frequency variations (brightness or harshness) depending on the chip used.
  • Input Stage Role: In Class A/AB amplifiers, the input stage (op-amp) is generally just a pre-amplifier stage. While it sets the input impedance, it is less critical to the final output signal's integrity compared to the switching modulator of a Class D amplifier.
  • Modern Class D Design: In older or budget Class D designs, the lack of post-filter feedback made them more sensitive to the op-amp choice. Newer, high-end designs (like Purifi) are less susceptible to these changes.
    Ooberpad +4
Note: While op-amps often make a more noticeable, or "tunable" difference in Class D, the perception of better sound quality is highly subjective.
StereoNET +2
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Hope that helps.
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I didn't say anything about surround sound. No one questions the value of biamping. None of what you posted has anything to do with my comment. How is it possible that you don't hear what all the Rs, Ls, and Cs in the crossover do to the signals but you can hear differences between op-amps?
 
peterp1 said:
There is probably some good info here, because the testing is at least "apples to apples"

(even if they are slightly spoiled apples :) - see below)

That said, I think ASR does all of it's power testing with a 1khz signal, instead of the using full-spectrum 20-20khz with a specified +/- deviation (in other words, ASR is far below what the FTC amplifier rule requires for specs). The 1khz is highly offensive for a site claiming to be about "science". And doubly offensive given that Class-D amplifiers naturally struggle to have flat response over the full spectrum (20-20khz). Class-D can be made to have flat response full spectrum, but it is far from guaranteed -- choosing 1khz hides the inherent weakness area of modern amps. Choosing a testing criteria of 1khz for power tests also has nothing whatsoever to do with music.
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DIN standard used to measure power at 1kHz, I think also at 1% THD like ASR uses. Compared to 20-20kHz measured at amplifier rated THD it usually results in a bit inflated figure, depends on the amp how much so but honestly I don't think it's a huge issue as long as you compare apples to apples. These days they seem to also measure power at 20Hz over at ASR and most amps seem to do just fine. It can be a bit misleading combined with the THD figures though, then again THD at 5W seems a more relevant number for listening to music than THD at max power, but of course that could be provided even if the max power was at rated THD.

I'm no expert but I see nothing terribly wrong with the way they measure things, but then again if it leads to things like chifi manufacturers using stupid low gain and input impedances to get seemingly better SINAD figures that might be an actual problem but it's not exactly the fault of the people doing the measurements, other than perhaps encouraging it.
 
Class D, hmmm, it's almost considered a dirty word in the audio world, as of now, I have an NAD D3120, Desktop integrated, a mere 30wpc, but it sounds great, I have connected it to ADS 300, 400, 520, and 880, and it performed well. Recently I bought an SMSL SA300 (2x40 @8ohms)w/Bluetooth, d/a, etc, this thing is pretty cool, it's size makes it perfect for a desktop solution, currently it is driving my L520's effortlessly, what an amazing little wonder. I do own some class A/B stuff and I love it, especially for my larger ADS 3ways. But as an older audio guy, it's really nice that these new technologies are making HIFI attainable for the average income. Music should be enjoyed by everyone that can appreciate it's virtues.
 
muovimies said:
DIN standard used to measure power at 1kHz, I think also at 1% THD like ASR uses. Compared to 20-20kHz measured at amplifier rated THD it usually results in a bit inflated figure, depends on the amp how much so but honestly I don't think it's a huge issue as long as you compare apples to apples. These days they seem to also measure power at 20Hz over at ASR and most amps seem to do just fine. It can be a bit misleading combined with the THD figures though, then again THD at 5W seems a more relevant number for listening to music than THD at max power, but of course that could be provided even if the max power was at rated THD.

I'm no expert but I see nothing terribly wrong with the way they measure things, but then again if it leads to things like chifi manufacturers using stupid low gain and input impedances to get seemingly better SINAD figures that might be an actual problem but it's not exactly the fault of the people doing the measurements, other than perhaps encouraging it.
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Honestly, it matters a lot and what he is doing is complete crap. What matters is not the power it can generate at each frequency. If an amp puts out 100 watts at 1khz, and 80 watts at 20hz, what does that tell us? The answer is absolutely nothing. The only thing that matters is how "flat" the frequency response is, worst case +/- in dbs, across the entire 20-20khz frequency spectrum, at all volume levels up to the rated power. How flat it is from min to max power is far more important than THD (since 1% THD, for example, isn't even audible). If an amp at 10 watts, or whatever watts, is down 3db at 20hz and down 4db at 18khz, that is the epitome of not qualifying as "HiFi", and you won't see that at all in his stats.

There are three reasons full-spectrum stressed testing matters:

1) Music is not 1khz -- it's all frequencies 20-20khz with a signal profile a gazillion times more complex than a 1khz Sine wave (listen to the "1khz test tone" and the "Dazed and Confused" YouTube links I posted previoulsy -- if you listen closely you'll hear a difference :):))

2) While it is inherently easy for Class-A and AB amps to be flat across the entire spectrum at all power levels (almost a given) -- it is inherently difficult to achieve that with Class D amplifiers that naturally have roll-off at the lowest frequencies and highest frequencies. There are designs that can make Class-D flat, but that isn't the default or a given. He's using a test criteria that intentionally ignores the biggest weak point of Class D amps.

3) The FTC Amplifier Rule (Federal Register :: Request Access) requires the testing to be at rated power, 20 Hz to 20 kHz without exceeding 1.0% THD+N into 8-ohms sustained continuously for not less than 5 minutes -- he uses 1khz, I think for only a few seconds. You can't anoint yourself the king of science, challenging the manufacturer's claims, when you are using evaluation "criteria" that are a tiny fraction of what the manufacturers you are challenging are required to use. Metaphorically speaking, the manufacturers are required to use "chess" for testing standards, he's evaulating amps at "checkers" -- and class-D amps are inherently weak at chess unless the design is carefully done.

I wasn't familiar with the European testing standards, but looked them up because I was curious what they are. The DIN HiFi standards are complete crap (40hz-16khz) first established in 1966. It looks like they have been superseded by EN IEC 60268-3:2018 (5th Edition) It's hard to find the exact text of that standard, but the AI summary says that it's very similar to the FTC standards with 20-20khz testing. The EN IEC standard seems to go beyond the FTC by recognizing that Class-D amplifiers are sensitive to impedance changes and require specialized testing across various load impedances. Class A/B work uniformly across impedance loads (just need to worry about total currrent in very low impedance loads) -- another reason why class-D need to be tested more stringently than Class-A/B, not a million times less stringent.
 
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muovimies said:
DIN standard used to measure power at 1kHz, I think also at 1% THD like ASR uses. Compared to 20-20kHz measured at amplifier rated THD it usually results in a bit inflated figure, depends on the amp how much so but honestly I don't think it's a huge issue as long as you compare apples to apples. These days they seem to also measure power at 20Hz over at ASR and most amps seem to do just fine. It can be a bit misleading combined with the THD figures though, then again THD at 5W seems a more relevant number for listening to music than THD at max power, but of course that could be provided even if the max power was at rated THD.

I'm no expert but I see nothing terribly wrong with the way they measure things, but then again if it leads to things like chifi manufacturers using stupid low gain and input impedances to get seemingly better SINAD figures that might be an actual problem but it's not exactly the fault of the people doing the measurements, other than perhaps encouraging it.
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All these numbers and comparisons based on numbers mean very little (jos korviin sattuu). Many of the measurements can look identical on paper or even very bad but the sound quality is good. This is very true with affordable Class D Amps that are tuneable by Op Amps (riippuu jos korvat pelaa).
 
The Only Class D amp that I have is the module of my DIY Subwoofer : an ATOHM S250... Which does the job flawlessly.

25120108525925019418681416.jpg


One of these days, I'll buy a little Chinese class D Hi-Fi ( = wideband audio), the question is : which one ? I mean : flawless, but not too costy too... :idea::idea::idea:

T
 
tubelectron said:
The Only Class D amp that I have is the module of my DIY Subwoofer : an ATOHM S250... Which does the job flawlessly.

25120108525925019418681416.jpg


One of these days, I'll buy a little Chinese class D Hi-Fi ( = wideband audio), the question is : which one ? I mean : flawless, but not too costy too... :idea::idea::idea:

T
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That looks very cool. Nicely done.
 
I never thought that I would use the words "good looking" in an unironic way when describing a subwoofer.

Wow. That is a beauty. Nice work!
 
P.M.B.66 said:
Rs (Right Surround), Ls (Left Surround) and Cs (Center surround). Your question make no sense to me.
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Oh FFS! Crossovers are made using Resistors (Rs), Inductors (Ls), and Capacitors (Cs). I specifically said "Rs, Ls, and Cs IN THE CROSSOVER".
So again, my questions is how can you not hear what those components IN THE CROSSOVER do, and yet your hearing is so finely tuned that you hear differences between op-amps?
 
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mrehorst said:
Oh FFS! Crossovers are made using Resistors (Rs), Inductors (Ls), and Capacitors (Cs). I specifically said "Rs, Ls, and Cs IN THE CROSSOVER".
So again, my questions is how can you not hear what those components IN THE CROSSOVER do, and yet your hearing is so finely tuned that you hear differences between op-amps?
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Op Amps are still the only variable. What's your point? You are talking about Passive Bi Amping with gain control? And you presume the crossover is not bypassed? You are mostly right as that crossover loses it purpose to distribute power now that you control the High and Low separate. But it is still there for the function of separating frequencies.

For Op Amps ask a question: Why do op amps make a difference in Class D and not on class A and AB.

Op-amps make a more noticeable difference in Class D amplifiers compared to Class A or AB because of their vastly different roles in the signal chain. In Class D, the op-amp is critical to the modulation and feedback loop, whereas in Class A/AB, it is typically used only for low-level pre-amplification.
Avnet +1
Here is a breakdown of why this difference exists:

1. The Role of Op-Amps in Class D (Critical)
Class D amplifiers convert analog input into a high-frequency Pulse Width Modulation (PWM) signal.
What Hi-Fi?
  • Modulation & Comparator Function: The op-amp is often used as a high-speed comparator, comparing the input audio signal with a triangle wave to generate the PWM signal.
  • Impact of Performance: The speed, precision, and noise of the op-amp directly dictate how accurately that PWM signal is generated. A poor op-amp here causes distortion and "grainy" sound.
  • Feedback Loop: Modern Class D amps use heavy negative feedback to overcome linearity issues. The op-amp often acts as the front-end processor in this closed-loop system, directly affecting the overall frequency response, distortion, and power-supply rejection.
  • Input Sensitivity: Class D amps are often highly sensitive to noise in the input signal, meaning the quality of the pre-amp op-amp matters more.
    Analog Devices +4

2. The Role of Op-Amps in Class A/AB (Less Critical)
Class A/AB amplifiers are linear, meaning they amplify the signal directly without switching.
Crutchfield +3
  • Pre-amp Only: In these systems, op-amps are usually only found in the input buffer or pre-amplifier stage, not in the power stage that drives the speakers.
  • Robustness: Because the main amplification is done by robust, often discrete transistors, the overall sound is less dependent on the specific op-amp used at the input stage.
  • Lower Frequency Operation: Linear amplifiers do not need to generate 500kHz+ switching waveforms, making them less sensitive to the high-frequency limitations of op-amps.
    REL Acoustics +4

Summary Comparison
  • Class D: The op-amp dictates the switching quality, feedback, and accuracy of the signal conversion.
  • Class A/AB: The op-amp provides low-level input gain; the main sound character is determined by the output stage transistors.
    Crutchfield +4
In short: Changing an op-amp in a Class D amplifier changes how the entire signal is created, while changing one in a Class AB amp mostly just changes the pre-amp stage.
 
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