boXem Arthur 4222/E1 Amplifier Review

[boXem]

Where is the documentation or review of this unit being pushed to its limits before shutoff. That is the only reason anyone buys this over the 1ET400a. Unless you just want bragging rights. The 1ET400a handles 2 ohm loads.

A power sweep in 2 Ohm is quite stressful for the amp. Some very well regarded amps shutdown before the 4 Ohm sweep is complete.
But you are right, this is not a power stress test by itself. Our amplifiers need to withstand the CTA-2034 noise (i.e. crests at 700W, average at -12 dB) in 2 Ohm during 30 minutes. If it shuts down before, it will not got on sale in this form. Looking at you stereo Hypex NC500 OEM...

I never heard about a 1ET400A shutting down due to thermals. I rarely heard about the 1ET400A clipping into very difficult loads. The 1ET7040SA avoids this.

On a side note, I find quite interesting that boXem has been criticized several times in this thread for basic engineering stuff (choice of power supply, thermals, ...) while being the only small company led by an actual engineer, moreover with 24 years of practice (who admittedly is not very patient, is not always polite and [email protected] at marketing ).

So, now that I have 5 minutes, some engineering basics as a starter.

1. To reach and use the 950 W in 2 ohm from the datasheet, you need
- a power supply with +/- 72 V rails, to avoid amplifier clipping
- a power supply able to output 1035 W (950 W at the output + 85 W of losses) to avoid the power supply to collapse
Although almost all of them advertise such a power, I am not aware of a single amplifier sold with such a power supply.

2. Once the power supply rails can reach values above or equal to 70V, you can't use binding posts with metal parts within reach if you want to sell in EU. I am again not aware of an amplifier meeting these two criteria.

3. For good cooling, you need
- high thermal conductivity
- low thermal mass
- as much surface as you can
A big block of aluminum doesn't tick one of these.

 

[Rottmannash]

I appreciate educative answers. It's correct but remains on the dogmatic side of the argument. My comment wasn't about labelling or categorizing products, but features. Just to create a little bit of extra value which competitors may not offer. So anything of substance to object rather than educating about how a classic 3-link audio setup should look like?

I, for one would not consider purchasing any amp that included tone controls, as I would want the most accurate reproduction from the amp and introduce any DSP prior to it hitting the amp. I believe most would as well, so that may why you won't see many high spec amps including tone controls.

 

[Mnyb]

I, for one would not consider purchasing any amp that included tone controls, as I would want the most accurate reproduction from the amp and introduce any DSP prior to it hitting the amp. I believe most would as well, so that may why you won't see many high spec amps including tone controls.

I thinks it’s a pity that tone controls got removed from so called high end products .

 

[vicenzo_del_paris]

This review thread is about a power amp, not an integrated amp.
It is not the purpose of a power amp to provide tone controls.

One can create a specific thread about the trend in the absence of tone controls in integrated amps (btw why would you need tone controls when you can have full control using DSP?)

 

[DonH56]

Power amps are meant to provide power, not control and processing features found in integrated amplifiers or preamplifiers. Different product space, and the people needing power amplifiers are not likely to want to pay for features they do not need and not normally included in the product category. As well complain about a preamplifier that does not have sufficient power to drive your speakers.

I completely agree with @vicenzo_del_paris and many others who have lamented to loss of simple bass and treble knobs on many products. So many times I wanted to tweak the bass when listening at a low level, or turn down the treble a bit when playing louder.

 

[Mnyb]

I get that a power is a power amp , but if one build a so called pre amp it’s not feature complete without tone controls and the other stuff that’s got removed in the high end era like the balance control phono input stage . It can be a digital solution but the stuff needs to be there.

I also would like my power amps pretty much just as for example boxem builds them adjustable gain being a very wanted feature but not much more.

 

[Phorize]

I appreciate educative answers. It's correct but remains on the dogmatic side of the argument. My comment wasn't about labelling or categorizing products, but features. Just to create a little bit of extra value which competitors may not offer. So anything of substance to object rather than educating about how a classic 3-link audio setup should look like?

Well, as said above the assumption is that whatever is upstream from the amp is doing tone control if it’s needed, a good assumption I think.

 

[RustyGates]

I wonder how this compares to the March Audio P501 1ET7040SA monoblock. https://www.marchaudio.com/product/p501-mono-block-power-amplifier/?v=6cc98ba2045f

That one uses a custom PSU which is oversized...

"The main power supply is custom designed and is a significant improvement over the Hypex seen elsewhere. It has very low noise with high current output and excellent voltage regulation. Efficiency is improved with power factor correction."

And from my chat with Alan:

"I’m afraid there is not too much else I can reveal about the new PSU. Please note that Hypex do not produce a PSU with the correct voltage for the new Purifi 1ET7040SA module. The Hypex SMPS1200A400 is only 63v which is not high enough to allow the 1ET7040SA to reach full power rating of 500watts into 4 ohms. I have seen some manufacturers using this PSU with the 1ET7040SA, and whilst it will work, they are misleading customers if they state it will reach the rated power output.

The Hypex PSUs generally are actually not particularly sophisticated. One big problem it has is its output voltage is proportional to the mains input voltage. If the mains voltage dips below the nominal 230v or 110v, then so will the PSU output voltage by the same ratio. This again can lead to limited power output (e.g. with Purifi 1ET400 based amps)."

 

[boXem]

 

[RustyGates]

What's up with the 45kHz BW ballooning in the last graph. Hopefully the same measure over a 20kHz BW looks flat like the data sheet...

 

[Matias]

What's up with the 45kHz BW ballooning in the last graph. Hopefully the same measure over a 20kHz BW looks flat like the data sheet...

View attachment 236464

Amir's graph uses 45 kHz bandwidth, while Purifi's probably 20 kHz bandwidth.
That means 10 and 15 kHz in Amir's graph shows increased distortion as the bandwidth captures the 2nd and 3rd harmonic components, while Purifi's filters them out as they are inaudible.

Bruno has designed the feedback loop to maximize its efficiency in the audible range, and they show it with their graphs, but if you expand the bandwidth and measure distortion that is inaudible it is there, just dirt hidden under the carpet so to say.

 

[pma]

THD+N measured with 20kHz BW shows distortion only up to 10kHz (H2), or 6.67kHz (H2, H3). It is rather a marketing trick than a serious measurement. It is used to hide drawbacks of class D amplifiers. The plot above 10kHz is nothing but noise. It should be understood that harmonics above 20kHz, though inaudible, may interfere and create intermodulation products in audible band.

 

[RustyGates]

THD+N measured with 20kHz BW shows distortion only up to 10kHz (H2), or 6.67kHz (H2, H3). It is rather a marketing trick than a serious measurement. It is used to hide drawbacks of class D amplifiers. The plot above 10kHz is nothing but noise. It should be understood that harmonics above 20kHz, though inaudible, may interfere and create intermodulation products in audible band.

There's a reason why Bruno limits the measures to 20kHz, it's because this -
https://audiosciencereview.com/foru...-of-purifi-1et400a-amplifier.7984/post-194984

And CCIF IMD results is that (the 400A module) -

And the 32-tone test is clean for the 7040.

 

[Haskil]

Power amps are meant to provide power, not control and processing features found in integrated amplifiers or preamplifiers. Different product space, and the people needing power amplifiers are not likely to want to pay for features they do not need and not normally included in the product category. As well complain about a preamplifier that does not have sufficient power to drive your speakers.

I completely agree with @vicenzo_del_paris and many others who have lamented to loss of simple bass and treble knobs on many products. So many times I wanted to tweak the bass when listening at a low level, or turn down the treble a bit when playing louder.

Bonjour,

A lot of professionals amplifiers have DSP included with a lot of correction and filters.

It was not high-end electronics that removed tone correctors, subsonic filters, adjustable loudness and other filters, but the small British brands that marketed ordinary electronics pretending that they were top-of-the-range by precisely removing everything that supposedly took away from the purity of sound and "musicality"... During this time, the great electronics Accuphase, Quad, Sony, McIntosh, ML and others kept them... It must be said that making this type of corrections and filters for cheap while being efficient was not within the reach of Rega, Linn or NAIM in the years 1970-1980... Audiophile clichés, rather idiophiles, being very powerful, they had the skin of correctors and other filters... Except the worst of all: the RIAA corrector

 

[restorer-john]

I completely agree with @vicenzo_del_paris and many others who have lamented to loss of simple bass and treble knobs on many products. So many times I wanted to tweak the bass when listening at a low level, or turn down the treble a bit when playing louder.

Go vintage @DonH56 !

I don't own a preamplifier without the 'basics'- even if 99% of the time they are bypassed and out of circuit. It's that 1% of the time when they are indispensable.

 

[restorer-john]

There's a reason why Bruno limits the measures to 20kHz, it's because this

No, it's because he wants to sell amplifiers, that's all. He's attempted to rewrite, in various ways, the measurement bandwidth narrative to suit their agenda, but it won't work.

On the one hand, they'll tout wide bandwidth source material as being beneficial with something like the Mola Mola Tambaqui with this fabulous HF IMD response...

Stereophile Jan 2022

But on the other hand, they want to brick wall filter at 20kHz when it comes to amplification specifications. I can see why...

 

[pma]

There's a reason why Bruno limits the measures to 20kHz, it's because this -
https://audiosciencereview.com/foru...-of-purifi-1et400a-amplifier.7984/post-194984

And CCIF IMD results is that (the 400A module) -

And this is another IMD test, TDFD, with NC252MP (I have no Purifi amp) and 45kHz BW:

First, measurement loopback

IMD = -99.3dB

with NC252MP, 79W power

Please note the IMD products falling into 20kHz range.

Please compare values of d2L, d4L of both plots. And the forest of new components between 8kHz - 20kHz.

 

[DonH56]

Bonjour,

Hi!

A lot of professionals amplifiers have DSP included with a lot of correction and filters.

Yes, though I would argue those target a different market. Most audiophiles own a preamp or processor to handle those functions. Integrating them into a power amplifier is a marketing decision as well as a design decision. It adds cost, complexity, and potentially a lot of extra work for the designer of an otherwise basic amplifier. A small shop may not have the knowledge, resources or desire to add those features. Again, that is a decision the manufacturer must make, whether it is worthwhile to pursue that market.

Bringing it up for consideration is certainly worthwhile, then it is up to @boXem | audio to decide if it makes business sense. The end result could be a family of basic amplifiers, amplifiers with DSP or simple tone controls, and integrated amps adding input switching. But that is a significant step for a one-man show. He may prefer to stay in his niche. Not my call.

It was not high-end electronics that removed tone correctors, subsonic filters, adjustable loudness and other filters, but the small British brands that marketed ordinary electronics pretending that they were top-of-the-range by precisely removing everything that supposedly took away from the purity of sound and "musicality"... During this time, the great electronics Accuphase, Quad, Sony, McIntosh, ML and others kept them... It must be said that making this type of corrections and filters for cheap while being efficient was not within the reach of Rega, Linn or NAIM in the years 1970-1980... Audiophile clichés, rather idiophiles, being very powerful, they had the skin of correctors and other filters... Except the worst of all: the RIAA corrector

I do not know who started the trend, but there were a number of manufacturers who eschewed tone controls in the 1980's when "straight wire with gain" and "pure signal path" proponents (zealots?) demanded their removal. It got really crazy, with some folk going so far as to solder wires inside the box to bypass all switches, making a single-purpose (single-input) device. All in pursuit of the "purest" sound. I noted then as I note now that the studio recording, mixing, and mastering process is hardly a straight path... And having the ability to correct for the room, speakers, or just a recording you do not like the frequency balance of, is still A Good Thing in my book.

I thought most if not all ML preamps did not have tone controls? Foggy memory... He added them back with the Cello series.

 

[DonH56]

No, it's because he wants to sell amplifiers, that's all. He's attempted to rewrite, in various ways, the measurement bandwidth narrative to suit their agenda, but it won't work.

On the one hand, they'll tout wide bandwidth source material as being beneficial with something like the Mola Mola Tambaqui with this fabulous HF IMD response...

Stereophile Jan 2022

View attachment 236587


But on the other hand, they want to brick wall filter at 20kHz when it comes to amplification specifications. I can see why...

Those look like (very) poorly suppressed images from the DAC, not IMD, at least the large spurs around 25 kHz. The IMD2 spurs should be up around 40 kHz. So, not an issue with the amplifier? But not a DAC I'd care to own, unless it has another image-suppression filter setting that does a better job. And yah, having the amplifier bandwidth to send them on to the speakers is not necessarily a feature...

 

[Scytales]

I don't own a preamplifier without the 'basics'- even if 99% of the time they are bypassed and out of circuit. It's that 1% of the time when they are indispensable.

That is so true !