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boXem Arthur 4222/E1 Amplifier Review
- Thread starter amirm
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Ajax
Senior Member
There is also the Topping DM7, 8 channel DAC for only US$599. Amir found it to measure very well. It has a USB input.
Topping DM7 8-Channel DAC Review
This is a review and detailed measurements of the Topping DM7 8-channel balanced USB DAC. It was sent to me by the company and costs US $599. The DM7 is simplicity in itself as you can tell from its rear terminals: USB input is the only one provided which is just fine with me. And seems...
www.audiosciencereview.com
You could feed this into any number of hypex based amps with 4, 6 & 8 channels from the likes of Buckeye & Audiophonics.
Audiophonics
www.audiophonics.fr
Buckeye Amps: New US based Hypex multichannel amplifier builder, line-up announcement!
Hypex NC502MP Power Specs (1kHz, THD = 1%): - 450w @ 2ohm (per channel, peak) - 500w @ 4ohm (per channel, peak) - 350w @ 8ohm (per channel, peak) Hypex NC252MP Power Specs (1kHz, THD = 1%): - 180w @ 2ohm (per channel, peak) - 250w @ 4ohm (per channel, peak) - 150w @ 8ohm (per channel, peak) XL...
www.audiosciencereview.com
Good luck
..and this is how to do itNow I feel like a politician in front of an interviewer.
So, since you both kindly asked, let me tell you about these points.
- active common mode rejection: to transmit a signal, two potential V+ and V- are needed. Differential voltage is defined as (V+ - V-), common mode voltage is defined as (V+ + V-)/2.
To simplify, common mode is perturbations, differential is signal. All the game is to avoid perturbations to mix with signal, that is called common mode rejection.
To do this, the idea is that the amplifier input presents an impedance as high as possible to common mode signals. With adequate topology and resistors tolerance, this is relatively easy to do. Until you add an EMI filter with it's capacitors whose impedance will dramatically decrease with frequency. 2 x 100 pF at 20 kHz is équivalent to 40 kOhm, far away from the MegOhm that we want to reach.
Then enters Mr. Bill Witlock whose capacitive bootstrap technique patent is now in public domain. We can now have both excellent CM rejection at audio frequencies and good EMI rejection. Since this technique uses active components, we called it "active" common mode rejection.- ultra low noise buffer: for various reasons (bigger FETs but also modulator topology) the 1ET7040SA is 40% noisier than the 1ET400A.
For the 4215/E2 we chose OPA1656 opamps for the buffer. Their low bias current allows both low DC at amplifier output (no thump at power on/down, less speaker distortion) and input impedance while their noise is low enough to allow excellent THD+N and SNR values.
Since we knew that the cost per channel would be multiplied by two for the reasons that I explained previously, performance of the new amp had to be at least equal to the 4215/E2. Buffer noise had to at least decrease as much as the module noise increased.
So bye bye OPA1656, hello OPA1612, a lot of work on the choice of resistors and the layout, then target was achieved. As shown by the measurements, the buffer has no footprint at low and medium gain.
Some will notice that I didn't talk about low noise regulators. In addition to be in unobtainium, they are completely useless with modern opamps. So we don't use them for this application.- high pass response: OPA1612 has a quite high bias current, so if you mix it with an elevated input impedance, you will get a lot of DC at the output. Since we want our amps to be easy to drive, even with tubes, high input impedance is not negotiable. And high DC output is not acceptable. The solution was to AC couple the buffer to the module.
- u-shaped buffer: I will leave some mystery here, but the members having followed the discussion around the glorified ribbon will understand.
not a plethora of silly custom OP-amps (hello nord ) in sigth , just be the engineer and pick the rigth parts for the job.+ for not lovering the input impedance and still get stellar performance
Primare
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GATO
According to measurements, yes. Not that the difference is audible.
Right. As you said "SQ", I would have thought you implied that the measurable difference would be audible.
After this reply of yours, I have tried to imagine a situation where the difference would be audible. Perhaps with extremely sensitive speakers, there are some transducers that reach 111Db/W/m; then, MAYBE one could hear a difference in noise level.
But why on earth would a reasonable person drive such speakers with those Purifi amps?_
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The peak power is about 400watts, how did it do that? It's so amazing.
PS is not regulated.
I’ll take issue with the amplifier. The 1ET7040sa is supposed to have beefier thermals to handle the heat of crazy loads but it is standard looking case without any additional cooling features. I’ve said in other threads that even the 1ET400a handles 2 ohms but is thermally limited. I’m sure the unit has stellar measurements but that is not the sole purpose of this amp.
The only massive heatsink designed case that I’ve seen appropriate for this module is the Apollon PET 950 which comes with a nosebleed price. I was hoping others would pay attention to the importance of cooling.
The only massive heatsink designed case that I’ve seen appropriate for this module is the Apollon PET 950 which comes with a nosebleed price. I was hoping others would pay attention to the importance of cooling.
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@amirm did you experience thermal issues when testing the amplifier?
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.
pickyAudiophile
Active Member
Sadly none of these builds by boxem, Audiophonics and others comes at least with basic tone control (Bass, Treble in 1 dB steps -> I don't ask for anything more) just to offer a little bit of extra value.
I'm so happy ever since with amplifiers which have that feature built in. Currently running dual mono SMSL A300 with treble setting at +2 and bass at -1. If I ever wanted to keep these basic settings with a Purifi or NCore solution it would cost me so much more than just buying these power amps. While "ruining" their impressive specs with a preamp in the middle.
I'm so happy ever since with amplifiers which have that feature built in. Currently running dual mono SMSL A300 with treble setting at +2 and bass at -1. If I ever wanted to keep these basic settings with a Purifi or NCore solution it would cost me so much more than just buying these power amps. While "ruining" their impressive specs with a preamp in the middle.
Well these are power amps, you will always need a preamp or something before, even if only for volume control...
People buying these have that solved (if they want to) upstream.
pickyAudiophile
Active Member
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?
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 s@cks 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.
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 appreciate educative answers
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