Purifi vs. Pascal - What is going on?

[boXem]

Would you care to elaborate please? I'd considered the exact same measurements, but came to the conclusion that, assuming purifi's "1m! on the scale means 1 miliohm, the purifi has much less output impedance, and much less rise in output impedance, relatively speaking - however even though the pascal has a greater amount and a bigger rise, its quite far up in the frequency spectrum, and if anything, rising output resistance would reduce, not increase treble?
But on the other hand if the Purifi's rise in output impedance is actually great enough to be audible, the way it graphs, it starts so early that under a low resistance load, if it rolled off frequencies in that same inverse manner, that would I think correspond pretty well with what I heard...

Because assuming I'm correct in saying rising output resistance, would reduce voltage/linearity in the given area, relative to the rest, i.e. would roll off upper frequencies, and more so the lower resistance the connected load is, and assuming the output resistances of both amps are high enough to affect linearity to an audible degree, due to the non-linear nature of the resistance (which I'm aware would be dubious, as both with conventional "good enough" reasoning, should be low enough as a whole and would be best to actually test.), and presuming the non-linearity of either amps impedance is equally audible (fx. if the purifi scale is ohm, not miliohm), simply looking at where they would be rolling off:
Then the purifi would theoretically start seeing some degree of roll-off or reduction in relative level already from 3-400Hz, increasing at the frequencies rise, which would produce a warmer/more rolled off sound, more so than the Pascal arguably, which only begins to really have rising resistance at 2-3kHz,, an only steeply rising much later.

I don't know if that is what you hinted at, but assuming all of the above is true, and is audible, then I think it would line up with, and likely explain what I was hearing.

It would also possibly explain why the difference was more audible on my JBL Ti10k vs. the Dynaudios, as the JBL is very sensitive, and from 70hz up is around 4Ohm, where as the Dynaudios are not efficient, but fairly stable at 6Ohm, going to 5 at their lowest - in other words, the JBL's lower impedance, would exacerbate the above issue, relative to a higher impedance speaker like the Dynaudio.
Though this may also simply be a result of the Dynaudios low efficiency, which I know has been correlated to speakers being much less audibly affected by characteristics of the chain they're connected to...

Frequency response is mainly a result of the output impedance vs. frequency, I was used to look at the frequency response but with time I started to prefer the output impedance. They are two ways of looking at the same thing.
1. The frequency response:
The difference between the Purifi and the Pascal is that the Pascal is not load invariant. We see that from 5 kHz, the response of the amplifier is changing with the load attached. Since the speaker impedance is far to be flat, some frequencies above 5 kHz will be emphasized (high speaker impedance), others attenuated (low speaker impedance). For an amplifier that is not load invariant, the Pascal is well behaved, in the sense that it doesn't amplify anything. Since in general speaker impedance is still low around 5 kHz but is rising further away, one can assume that frequencies in the 5-7ishes kHz may be attenuated. Higher frequencies will be less attenuated due to higher speaker impedance, lower frequencies the same but due to the load invariance. So a first source of coloration comes here. In comparison, since the Purifi is completely load insensitive, it will not add any coloration.
2. The output impedance:
Depending the frequency, the Purifi output impedance is between 0.05 and about 0.65 mOhm. For a speaker impedance of 4 Ohm, this corresponds to an attenuation between 0.0001 and 0.0014 dB.
In comparison, the Pascal output impedance is between 6 and about 150 mOhm. Still for the 4 Ohm speaker impedance, this is an attenuation comprised between 0.013 and 0.3 dB.
Since the speaker impedance is not constant, some frequencies will be attenuated, some other not. We consider that level matching is mandatory because human ear is able to discern differences of 0.1 dB. You can see that this threshold is reached in the case of the Pascal. A coloration is introduced.
While we have a tendency to consider that level matching erase all differences, it is only the case for comparison between gear with flat frequency response. The problem is that amplifiers loaded with speakers do not have this property. If levels are matched at a frequency where amplifier A attenuates and amplifier B amplifies from a flat response, instead of being erased, differences will be highlighted.

 

[somebodyelse]

Don't quite know what you meab by "Clever Hans"?

https://en.wikipedia.org/wiki/Clever_Hans - the horse that could apparently do arithmetic turned out to be watching the unconcious reaction of the trainer.

 

[Lord Victor]

https://en.wikipedia.org/wiki/Clever_Hans - the horse that could apparently do arithmetic turned out to be watching the unconcious reaction of the trainer.

Ah, I see what you mean - I'll save that term for later use!

I mean its not impossible in some cases - though I sat behind them in most cases, or wasnt even there in a couple cases, they just wrote notes for me (because we didnt have time to meet). That and I've known as "Stone Face" because of my lack of facial expression/emotion, which I guess in this specific case could be a benefit, and not just signs of me being the next Hannibal Lecter

I doubt its the case, especially given the consistency, but yea not impossible of course, since we're in the realm of hobbyist bumbling rather than ideal lab conditions.

 

[Lord Victor]

Frequency response is mainly a result of the output impedance vs. frequency, I was used to look at the frequency response but with time I started to prefer the output impedance. They are two ways of looking at the same thing.
1. The frequency response:
The difference between the Purifi and the Pascal is that the Pascal is not load invariant. We see that from 5 kHz, the response of the amplifier is changing with the load attached. Since the speaker impedance is far to be flat, some frequencies above 5 kHz will be emphasized (high speaker impedance), others attenuated (low speaker impedance). For an amplifier that is not load invariant, the Pascal is well behaved, in the sense that it doesn't amplify anything. Since in general speaker impedance is still low around 5 kHz but is rising further away, one can assume that frequencies in the 5-7ishes kHz may be attenuated. Higher frequencies will be less attenuated due to higher speaker impedance, lower frequencies the same but due to the load invariance. So a first source of coloration comes here. In comparison, since the Purifi is completely load insensitive, it will not add any coloration.
2. The output impedance:
Depending the frequency, the Purifi output impedance is between 0.05 and about 0.65 mOhm. For a speaker impedance of 4 Ohm, this corresponds to an attenuation between 0.0001 and 0.0014 dB.
In comparison, the Pascal output impedance is between 6 and about 150 mOhm. Still for the 4 Ohm speaker impedance, this is an attenuation comprised between 0.013 and 0.3 dB.
Since the speaker impedance is not constant, some frequencies will be attenuated, some other not. We consider that level matching is mandatory because human ear is able to discern differences of 0.1 dB. You can see that this threshold is reached in the case of the Pascal. A coloration is introduced.
While we have a tendency to consider that level matching erase all differences, it is only the case for comparison between gear with flat frequency response. The problem is that amplifiers loaded with speakers do not have this property. If levels are matched at a frequency where amplifier A attenuates and amplifier B amplifies from a flat response, instead of being erased, differences will be highlighted.

Thank you! That was the exact sort of red thread I was looking for to start unraveling what might be going on!

The point you mention with level matching is the exact issue I've had when trying to level match between different devices: I've tried both doing it with test tones, or using peak output when playing back an identical track - in either case it doesn't always seem to give a perfect result when listening.

Back to the point, a difference of about 0.3dB sounds like it could plausibly be what I was hearing, I'd expect the differences to be bigger, or that something else might be going on as well, but its certainly the best bet I've seen thus far - and who knows what the actual impedance curves of some of these speaker actually look like: the JBL which showed the differences particularly strongly, are 4-way crossovers, with out of phase woofers, so their impedance curve could be quite... Interesting.

Whether this is enough to account for the entire 'thing' like the bass control/resolution, I don't know, but it could be, since higher frequency volume increase can give a perceived sense of transient precision/resolution/precision, making each sound seem more distinct - like clapping your hands together vs. hitting two cushions together.
Good start, and one of the most sane/useful answers I've ever gotten to one of my ventures of curiosity - thank you again! I'll have to look into this further to make sure I've understood it fully...

 

[daniboun]

I own lots of Class D amps, including the Dual Mono Pascal and Hypex Ncore + Purifi and other high ends TPA325X amps...
Without turning a blind eye, the Purifi is indeed a cut below all the others .... The Pascal is not bad but its price does not necessarily justify its purchase .... For an "average" budget I recommend the NC252MP who has the best of all these "worlds"

First picture = Pascal Dual Mono UPro (2x250W / 8 ohms)

 

[Lord Victor]

I own lots of Class D amps, including the Dual Mono Pascal and Hypex Ncore + Purifi and other high ends TPA325X amps...
Without turning a blind eye, the Purifi is indeed a cut below all the others .... The Pascal is not bad but its price does not necessarily justify its purchase .... For an "average" budget I recommend the NC252MP who has the best of all these "worlds"

First picture = Pascal Dual Mono UPro (2x250W / 8 ohms)

Huh, very interesting to hear! In fairness that is an entirely different Pascal amp, from a couple years earlier. But you're not the first end-user I've spoken to who have been under-whelmed by the purifi, which is interesting, given how much hype it has been garnering from 'reviewer' channels, amongst other. It might just be a matter of taste, hard to say...
At this point I'm probably going to go for the Pascal amp I was looking at, or possibly both... Or some other solution; not really sure anymore.

The literal only downside to the pascal to my ears was that clinical/cold tonal quality it had, aside from that it was miles ahead of pretty much anything else I've com across... But that being said that is also an important factor: it can be as audibly technically brilliant as it wants, if its not enjoyable to listen to then...
As Steve Guttenberg said, the best hifi system, is the one that makes you want to listen to more music. I'd caveat that with saying its the 'subjectively best', but I think thats a given. At the end of the day, I'm unsure if either of these amps fit that bill entirely; the Pascal might, if I can find a way to warm it up a bit.

The Purifi is brilliant on paper, and is load invariant, which is amazing, but at the end of the day its just mildly boring sounding in a way.

Tough choice.

 

[daniboun]

Huh, very interesting to hear! In fairness that is an entirely different Pascal amp, from a couple years earlier. But you're not the first end-user I've spoken to who have been under-whelmed by the purifi, which is interesting, given how much hype it has been garnering from 'reviewer' channels, amongst other. It might just be a matter of taste, hard to say...
At this point I'm probably going to go for the Pascal amp I was looking at, or possibly both... Or some other solution; not really sure anymore.

The literal only downside to the pascal to my ears was that clinical/cold tonal quality it had, aside from that it was miles ahead of pretty much anything else I've com across... But that being said that is also an important factor: it can be as audibly technically brilliant as it wants, if its not enjoyable to listen to then...
As Steve Guttenberg said, the best hifi system, is the one that makes you want to listen to more music. I'd caveat that with saying its the 'subjectively best', but I think thats a given. At the end of the day, I'm unsure if either of these amps fit that bill entirely; the Pascal might, if I can find a way to warm it up a bit.

The Purifi is brilliant on paper, and is load invariant, which is amazing, but at the end of the day its just mildly boring sounding in a way.

Tough choice.

I think that in HIFI the tastes and colors are in nature)
If you are looking for some Pascal Dual Mono amplifier > MP me )

 

[Synergy4]

When comparing minor differences in the sound of Class D amplifiers, one should really consider the source material, speakers & room resonances used for listening sessions. The specific conditions with all the components are used together may affect perception.

Back in around 1986, I went a local AES meeting in San Francisco where they were doing A/B blind testing of speaker wires. There were slight differences in sound, but I am not sure which was better- it seem to be a pointless endeavor.

"The search for the perfect solution is the enemy of a good solution"..... Articles that comes to mind.....

Analogue Warmth: https://www.soundonsound.com/techniques/analogue-warmth

Differences in Amp Sound: How Do We Find the Truth?: https://audioxpress.com/article/differences-in-amp-sound-how-do-we-find-the-truth

 

[Synergy4]

This looks like it might be an interesting paper, but I no longer belong to AES... Some people like the warmth of some types of distortion.

"Why Do Tube Amplifiers Have Fat Sound while Solid State Amplifiers Don't"

Shengchao Li
Article Number: 8536
Permalink: http://www.aes.org/e-lib/browse.cfm?elib=16062

 

[SIY]

There is more concentrated nonsense in this thread than is safe for innocent readers.

 

[Laserjock]

Has there been a Pascal based amplifier tested here?
I have a 3 channel D-Sonic and 2 channel Red Dragon Audio

 

[BDWoody]

There is more concentrated nonsense in this thread than is safe for innocent readers.

Maybe @amirm could do a video or two that show how to set up a listening test that might mean...something. Controls are such a drag though..it is much more fun to hear differences.

 

[Colonel7]

Has there been a Pascal based amplifier tested here?
I have a 3 channel D-Sonic and 2 channel Red Dragon Audio

The Jeff Rowland was Pascal IIRC

 

[Laserjock]

The Jeff Rowland was Pascal IIRC

Ahh yes, now I remember. Didn’t do so well.

 

[restorer-john]

Frequency response is mainly a result of the output impedance vs. frequency, I was used to look at the frequency response but with time I started to prefer the output impedance. They are two ways of looking at the same thing.

Not sure I agree with that. Input RC filters will not manifest their effects in output impedance. You can have 100% feedback at DC (RC in feedback loop) and a very low output impedance, but a deliberately rolled off bottom end or top end from the input RC values.

 

[Lord Victor]

Ahh yes, now I remember. Didn’t do so well.

Do we know which Pascal module it was - or if/how much Rowland had messed with it?

I know Gato uses M-Pro and S-Pro modules in theirs, and Aavik also uses pascal modules in theirs, though I don't remember which.

 

[Lord Victor]

When comparing minor differences in the sound of Class D amplifiers, one should really consider the source material, speakers & room resonances used for listening sessions. The specific conditions with all the components are used together may affect perception.

Back in around 1986, I went a local AES meeting in San Francisco where they were doing A/B blind testing of speaker wires. There were slight differences in sound, but I am not sure which was better- it seem to be a pointless endeavor.

"The search for the perfect solution is the enemy of a good solution"..... Articles that comes to mind.....

Analogue Warmth: https://www.soundonsound.com/techniques/analogue-warmth

Differences in Amp Sound: How Do We Find the Truth?: https://audioxpress.com/article/differences-in-amp-sound-how-do-we-find-the-truth

Yea, I'd tend to agree on the point of cables - I've heard cases of audible differences, and measurements I've seen did show up to a 0.5dB under certain conditions iirc, which is well above the 0.1dB generally agreed upon threshold of humans ability discern alterations; but on the other hand those are small enough differences, that I wouldn't particularly spend money on it, unless I was "rich" enough that the cost was of no consequence to me.
And it's rarely really a matter of "better", since I don't really think we have any definition for that with cables, beyond subjective opinion, since the differences are small enough to generally be disregarded.

I'd say the differences between these amps was quite a bit more noticeable, which is why I also doubt the previously considered output-impedance doesn't quite cover it, given that it would suggest a similarly small difference to a cable, which is usually something that's only really audible under very focussed conditions - the difference between these amps was fairly obvious, to the point where my mother, who's a pianist, not a hifi geek, quite quickly exlaimed that if she got around to getting a music system herself, she'd like a Pascal, because the acoustic instruments sounded much more real, compared to the Purifi which she though sounded dull by comparison.

The setup/room/system is definitely important, though the differences in these sorts of things tend to be fairly consistent, though it varies how obvious they are.
On the Dynaudio speakers, in a professionally built/treated room, the differences weren't that evident, but you could tell slightly, where as on the JBL's in my home setting, it was far more evident.

 

[Lord Victor]

This looks like it might be an interesting paper, but I no longer belong to AES... Some people like the warmth of some types of distortion.

"Why Do Tube Amplifiers Have Fat Sound while Solid State Amplifiers Don't"

Shengchao Li
Article Number: 8536
Permalink: http://www.aes.org/e-lib/browse.cfm?elib=16062

Its a serious shame that AES material isn't publicly accessible - there were several papers on there I wanted to study/reference in my recent examn project...

 

[boXem]

Not sure I agree with that. Input RC filters will not manifest their effects in output impedance. You can have 100% feedback at DC (RC in feedback loop) and a very low output impedance, but a deliberately rolled off bottom end or top end from the input RC values.

Agree. But in this case the response will not be load dependant.

 

[Sukram]

I would contact VTV, they have them all. I'm very happy with my VTV Purifi (no "improvements") after the NAD M10.