The state of the art class D AUDIOPHONICS HPA-S600NC and AUDIOPHONICS HPA-S400ET sound different, though there is a caveat here.

[SIY]

(some people claim, without evidence, to hear a difference, others don't

Fixed it for you.

 

[SIY]

Have you listened to them in isolation

No, amplifiers require loudspeakers to make any sound.

 

[ommadusk]

They've been swapped back and forth between two systems (dynamic and ESL) and between upper and lower part of my bi-amped dynamic system. They are both superb products offering lots of power and perfect transparency. I also have the Nilais and Axign, and same, they work perfectly for an audibility standpoint.

Yes.

No.

I have both a Purifi and an NCx500. Within power limits, they sound identical.

No, amplifiers require loudspeakers to make any sound.

You've claimed they sound the same 'identical' without objective evidence. Isn't that the same as me saying they sound different? Let's be consistent here. I was wondering if you listened to the amps in isolation from other speakers, if you used them with full range speakers, if they have matching power supplies, if they have matching OP amps, and what the sources are further up the chain, but according to you none of this matters. Lol

 

[Sokel]

You've claimed they sound the same 'identical' without objective evidence. Isn't that the same as me saying they sound different? Let's be consistent here. I was wondering if you listened to the amps in isolation from other speakers, if you used them with a full range speakers, and what the sources are further up the chain, but according to you none of this matters. Lol

The evidence is there to see.
Look at their measurements,in a nice integration audible noise will be zero so we leave that out.
What's left is the distortion.

If you think you can detect (hear) any of it down to this abyss is time to take the Klippel listening test.
Sometimes is disappointing but most of the time is liberating.

 

[Apollon Audio]

Interesting...

@Apollon Audio , @Audiophonics ,care to elaborate here?

If two power amplifiers measure the same or very close in terms of their specifications, but sound different when you listen to them, there are several potential reasons:

1. Measurement Limits: The measurements might not capture every aspect of an amplifier's performance. For instance, specifications might cover frequency response, total harmonic distortion (THD), and signal-to-noise ratio (SNR), but not capture other factors like transient response, intermodulation distortion, or phase distortion.

2. Load Interaction: Amplifiers can behave differently with different speaker loads. Even if two amplifiers measure similarly when tested with a resistive load, they might respond differently with the complex impedance of a real-world speaker.

3. Feedback Differences: Some amplifiers use negative feedback to reduce distortion, while others might use minimal feedback to achieve a specific sonic character. The amount and type of feedback can influence an amplifier's sound.

4. Circuit Topology: Different circuit designs, even if they produce similar measurements, can influence the sound. For example, a Class A amplifier might sound different than a Class D amplifier even if their specifications are similar.

5. Component Quality: The quality and type of components used (e.g., capacitors, resistors, transformers) can have an impact on sound quality.

6. Psychoacoustic Effects: Our perception of sound can be influenced by non-acoustic factors. For instance, knowledge about a brand, the look and feel of equipment, or the price can unconsciously alter our perception of sound quality.

7. System Synergy: Sometimes, the specific combination of components in an audio system (source, preamp, amp, speakers, cables) can make certain amplifiers sound better or worse. This is often referred to as "synergy" in the audiophile world.

8. Environmental Differences: Room acoustics, speaker placement, and even power quality can influence how an amplifier sounds in a particular setup.

9. Listening Volume: If you're comparing at different volume levels, even subtle, our ears perceive frequencies differently at different volumes (this is known as the Fletcher-Munson curves or equal-loudness contours).

10. Bias & Expectation: It's important to consider the potential influence of expectation bias. If you believe one amplifier should sound better because of its brand, reputation, or price, you might unconsciously perceive it as sounding better.

In the world of audio, measurements provide valuable information, but they don't capture the entirety of the listening experience. It's always beneficial to trust your own ears, in conjunction with measurements, when evaluating audio equipment.

I'd also like to clarify that I haven't stated a preference between Purifi and Hypex NCx500. While their measurements are closely aligned, they do have distinct sonic characteristics. My recommendation of Purifi to @soerenssen was based on his feedback regarding the performance of his Audiophonics NCx500 based amplifier.

 

[ommadusk]

The evidence is there to see.
Look at their measurements,in a nice integration audible noise will be zero so we leave that out.
What's left is the distortion.

If you think you can detect (hear) any of it down to this abyss is time to take the Klippel listening test.
Sometimes is disappointing but most of the time is liberating.

I will take the Klippel test, I couldn't get it to play on my PC last night. Do you know what resolution the clips are? It probably says. The result wouldn't change anything. I have an open mind.

 

[Sokel]

If two power amplifiers measure the same or very close in terms of their specifications, but sound different when you listen to them, there are several potential reasons:

1. Measurement Limits: The measurements might not capture every aspect of an amplifier's performance. For instance, specifications might cover frequency response, total harmonic distortion (THD), and signal-to-noise ratio (SNR), but not capture other factors like transient response, intermodulation distortion, or phase distortion.

2. Load Interaction: Amplifiers can behave differently with different speaker loads. Even if two amplifiers measure similarly when tested with a resistive load, they might respond differently with the complex impedance of a real-world speaker.

3. Feedback Differences: Some amplifiers use negative feedback to reduce distortion, while others might use minimal feedback to achieve a specific sonic character. The amount and type of feedback can influence an amplifier's sound.

4. Circuit Topology: Different circuit designs, even if they produce similar measurements, can influence the sound. For example, a Class A amplifier might sound different than a Class D amplifier even if their specifications are similar.

5. Component Quality: The quality and type of components used (e.g., capacitors, resistors, transformers) can have an impact on sound quality.

6. Psychoacoustic Effects: Our perception of sound can be influenced by non-acoustic factors. For instance, knowledge about a brand, the look and feel of equipment, or the price can unconsciously alter our perception of sound quality.

7. System Synergy: Sometimes, the specific combination of components in an audio system (source, preamp, amp, speakers, cables) can make certain amplifiers sound better or worse. This is often referred to as "synergy" in the audiophile world.

8. Environmental Differences: Room acoustics, speaker placement, and even power quality can influence how an amplifier sounds in a particular setup.

9. Listening Volume: If you're comparing at different volume levels, even subtle, our ears perceive frequencies differently at different volumes (this is known as the Fletcher-Munson curves or equal-loudness contours).

10. Bias & Expectation: It's important to consider the potential influence of expectation bias. If you believe one amplifier should sound better because of its brand, reputation, or price, you might unconsciously perceive it as sounding better.

In the world of audio, measurements provide valuable information, but they don't capture the entirety of the listening experience. It's always beneficial to trust your own ears, in conjunction with measurements, when evaluating audio equipment.

I'd also like to clarify that I haven't stated a preference between Purifi and Hypex NCx500. While their measurements are closely aligned, they do have distinct sonic characteristics. My recommendation of Purifi to @soerenssen was based on his feedback regarding the performance of his Audiophonics NCx500 based amplifier.

The question was about the two specific ones so I take the red bold is what matters with these two.
I won't comment cause our experts here must have a lot more to say about this.

 

[Sokel]

I will take the Klippel test, I couldn't get it to play on my PC last night. Do you know what resolution the clips are? It probably says. The result wouldn't change anything. I have an open mind.

After determining your listening threshold make sure you make the calculation about how many orders of magnitude lower these electronics have.
We all got our fair share of shock when we found out.

 

[ommadusk]

After determining your listening threshold make sure you make the calculation about how many orders of magnitude lower these electronics have.
We all got our fair share of shock when we found out.

Why would I be shocked? It's purely a test. I've got some hearing loss, I had a hearing test recently and I saw my audiogram. You're making assumptions.

 

[Apollon Audio]

The question was about the two specific ones so I take the red bold is what matters with these two.
I won't comment cause our experts here must have a lot more to say about this.

Before sharing my insights or subjective opinion, please note that I come with a background of 20 years as a mixing and mastering engineer. My ears have been finely tuned over the years to discern the most subtle nuances in audio. Furthermore, I operate within a meticulously acoustically treated room, complemented by a speaker system adept at revealing even the slightest distinctions in audio equipment or when sculpting sounds and audio.

Hypex NCx500: Often described as neutral and transparent, this module is regularly perceived as analytical by some listeners including myself, signifying its ability to reproduce recordings without adding any coloration. However, it's worth noting that with certain operational amplifiers, such as the LM4562 and similar types, the NCx500 can come across as slightly harsh in the high mids and highs. In my experience, this module pairs optimally with op amps like OPA1612, OPA1656, Weiss OP2-BP and similar, which tend to present a more refined sound profile.

Purifi 1ET400A: Also considered very neutral and transparent but might be perceived as having a touch more 'musicality' by some listeners including myself, which can mean a more engaging or warmer sound. However, this difference can be subtle and may not be noticeable in every system or to every listener. In my opinion, the Purifi 1ET400A exhibits a more refined and smoother presentation in the upper frequencies (high mids and highs) compared to the NCx500. Also Intriguingly, when integrated into certain systems, the Purifi 1ET7040SA for instance, imparts a noticeable influence on the sound profile. It seems to enhance the bass extension, making it sound deeper, more robust, and lending it a more assertive character.

 

[Sokel]

Why would I be shocked? It's purely a test. I've got some hearing loss, I had a hearing test recently and I saw my audiogram. You're making assumptions.

You're right I do make assumptions.
But my assumptions are based on the percentage amongst the listeners you'll see after the test.
Even that small top one.

 

[Sokel]

by a speaker system adept at revealing even the slightest distinctions in audio equipment or when sculpting sounds and audio.

May I ask which one (the speakers) ?
I'm genuinely curious about what companies use to determine SQ (everything else aside as room and speakers are the major players) so I do a little personal poll,it's not only about you.

 

[ommadusk]

Both Audiophonics and Apollon Audio recommended the Purifi. Indeed there are lots of contradicting info about their sound signature (some people hear a difference, others don't) and other than the different op amps I don't understand what else would explain the different perceptions.

For clarity, I thought somebody at Audiophonics said the S400ET (wrong assumption) sounded better than the NCX500 not the 1ET7040SA which they're not selling at the moment.

 

[JustJones]

Before sharing my insights or subjective opinion, please note that I come with a background of 20 years as a mixing and mastering engineer. My ears have been finely tuned over the years to discern the most subtle nuances in audio. Furthermore, I operate within a meticulously acoustically treated room, complemented by a speaker system adept at revealing even the slightest distinctions in audio equipment or when sculpting sounds and audio.

Hypex NCx500: Often described as neutral and transparent, this module is regularly perceived as analytical by some listeners including myself, signifying its ability to reproduce recordings without adding any coloration. However, it's worth noting that with certain operational amplifiers, such as the LM4562 and similar types, the NCx500 can come across as slightly harsh in the high mids and highs. In my experience, this module pairs optimally with op amps like OPA1612, OPA1656, Weiss OP2-BP and similar, which tend to present a more refined sound profile.

Purifi 1ET400A: Also considered very neutral and transparent but might be perceived as having a touch more 'musicality' by some listeners including myself, which can mean a more engaging or warmer sound. However, this difference can be subtle and may not be noticeable in every system or to every listener. In my opinion, the Purifi 1ET400A exhibits a more refined and smoother presentation in the upper frequencies (high mids and highs) compared to the NCx500. Also Intriguingly, when integrated into certain systems, the Purifi 1ET7040SA for instance, imparts a noticeable influence on the sound profile. It seems to enhance the bass extension, making it sound deeper, more robust, and lending it a more assertive character.

Thanks for sharing your subjective opinion. Do you think you could tell the Hypex from the Purifi in a blind test conducted in a fairly normal home environment? I couldn't, the Hypex was the NC500 not the newer x version.

 

[Apollon Audio]

I noticed while listening to more demanding genres like hiphop or in Rumble from Skrillex (around 1 minute into the song), the KEF's woofers seem to be struggling and at some point they get muffled for a moment, followed by a popping sound, but then it goes away immediately. I don't know if it's the speaker or the NCx500 amp.
To my ears, the combination of the NCx500 and Denon x4800h sound harsh in pure direct mode. For a nice bass level, I have to crank up the volume quite a lot and at that level it's not enjoyable anymore. Vocals are fine, acoustic guitar is already a bit harsh, and as soon as there are lot of instruments playing at the same time (metal, even jazz), it's too much, I have to turn the volume down. So basically I'm changing the volume all the time during a song.
It would be nice to have a good enough single-volume experience, but I don't know what should be the best way to achieve that: an upgrade to Purifi or using EQ/DSP (Dirac) on the receiver?

Like you, I was also told by Audiophonics (and Apollon too) that Purifi sounds warmer, less harsh, more musical. In your case, since both amps are from Audiophonics, the op amps are the same between the NCx500 and the Purifi, so that cannot explain the difference that you hear.

The phenomenon you're describing (I'm referring to your writing here and your PM you've sent to me) can be attributed to a combination of psychoacoustic effects, speaker design characteristics, and the non-linear behaviour of human hearing. Here's a breakdown:

Fletcher-Munson Curves (Equal Loudness Contours):

• Our ears perceive different frequencies differently at various volume levels. This psychoacoustic effect is described by the Fletcher-Munson curves. At lower volumes, our ears are less sensitive to low frequencies (bass) and very high frequencies (treble). As volume increases, our sensitivity to these frequencies becomes more linear, making bass and treble sound more pronounced.
• In simple terms, as you turn the volume up, bass frequencies might seem to "open up" or become more prominent simply because our ears become more sensitive to them.

Speaker Design:

• Some speakers are designed to perform optimally at specific volume levels. At low volumes, certain designs, especially larger ones with more massive drivers, might not move enough to produce bass frequencies effectively.
• Some speaker designs use ported or passive radiator systems to augment the bass response. These systems can become more effective at higher volumes when the drivers move more air.

Amplifier Interaction:

• Depending on the design and impedance curve of the speakers, some amplifiers might deliver better control and performance at higher volumes. If I'm not mistaken, Audiophonics uses LM4562 in their buffer design. This op amp is not the best choice for Purifi or Hypex in my opinion. Especially with the NCx500, it can sound harsh on mid highs and highs.

Room Acoustics:

• At higher volumes, room modes (resonant frequencies of a room) can be excited more, which might augment certain bass frequencies. This effect can make it feel like the bass is "opening up" at higher volumes, even if the speaker's output remains relatively consistent.
• I would certainly think about adding bass traps and moving the speakers closer to the rear wall, especially with 6,5 woofers that are built in your KEF's. You might be having some bass cancelation happening. Please read this writing from Genelec. It is very informative. https://support.genelec.com/hc/en-u...nough-bass-do-I-have-a-backwall-cancellation-

Compression and Dynamic Range:

• Some audio recordings or sources might use dynamic range compression, which can affect how bass frequencies are perceived at different volumes.

For those who often listen at lower volume levels but desire a full bass response, features like "loudness compensation" on some amplifiers or receivers can be useful. This feature boosts bass and treble at low volume levels to compensate for the human ear's reduced sensitivity to these frequencies at low volumes.

 

[antcollinet]

Thanks for sharing your subjective opinion. Do you think you could tell the Hypex from the Purifi in a blind test conducted in a fairly normal home environment? I couldn't, the Hypex was the NC500 not the newer x version.

Or @Apollon Audio even in the meticulously treated room you normally use.

Have you (@Apollon Audio) carried out the comparison blind and accurately level matched at all. (You must have expected this question here)

 

[JustJones]

Or even in the meticulously treated room you normally use.

Have you carried out the comparison blind and accurately level matched at all. (You must have expected this question here)

No, I didn't level match other than by SPL. My hearing isn't the best at 67 years old I didn't really expect to tell which was which. I've also tried with a Benchmark AHB, same outcome. My interest was if in a more normal home listening environment instead of a meticulous studio the subtle differences mentioned could be heard.

My room isn't meticulously treated, I use PEQ in roon to compensate for my pedestrian living room.

 

[Gorgonzola]

I don't scoff at people who hear sound differences between amp that measure so well that there ought to be no sound differences.

Personally I feel I've heard those sorts of differences -- although again in my own experience that these differences are very small. Nevertheless the individual may prefer one component over another and is entitled to do so. Frankly the hardcore objectivists are right: subjective differences can only be proven with ABX-type blind testing. So these subtle differences may be valid for the individual choices, but it cannot be assumed that these impressions will transfer from one individual to another except as a bias.

My own recent experience as been with Purifi I/O buffers and their op amps. I have a VTV Purifi Stereo. Originally I purchased it with the Hypex buffer: I hated the top-end, especially at higher sound level, schrill and unnatural sounding. I replace the Hypex with VTV's own buffer that permits easy op amp swapping. I tried several different op amps including the touted OPA1602, vintage OPA627, Burson V6 Vivid, but ended up preferring the Sparko SS3602.

... The implication of my exercise for you shouldn't be that the Sparkos op amp is the best, only that if you undertake as similar exercise, you might prefer one op amp over another.

 

[Apollon Audio]

May I ask which one (the speakers) ?
I'm genuinely curious about what companies use to determine SQ (everything else aside as room and speakers are the major players) so I do a little personal poll,it's not only about you.

May I ask which one (the speakers) ?
I'm genuinely curious about what companies use to determine SQ (everything else aside as room and speakers are the major players) so I do a little personal poll,it's not only about you.

The main speakers in my mixing and mastering setup are, ATC SCM 300, Amphion Two18 with BaseTwo25 subs, Neumann KH420 (not visible on the picture), Genelec 8351B. For our testing at Apollon we also use speakers like B&W 800 D3, Amphion 7LS, and some other brands.

 

[Apollon Audio]

Or even in the meticulously treated room you normally use.

Have you carried out the comparison blind and accurately level matched at all. (You must have expected this question here)

I place significant importance on blind tests when evaluating audio equipment. This approach minimizes biases and truly evaluates one's listening acumen. When conducting auditory comparisons, I predominantly rely on blind tests with accurately level matched equipment. In a soundproofed, acoustically treated room, I find it relatively straightforward to discern differences between amplifiers and other audio equipment. While home environments can present unique challenges due to reflections and room acoustics, with minimal interference, I believe one can still make accurate judgments.