BOXEM Audio | Arthur 4215/E2 Purifi Amplifier | Owners' Thread

[Hayabusa]

That's fine. My comment wasn't directed at you specifically, but there's been page after page of off topic cable debate in this thread at this point.

Do you have anything to say in regards to Boxem's 4215/E2?

You are right I was off-topic..

But I have (a Boxem) question:
The purify modules have an i2c interface that allows for detecting of clipping in the voltage and current domain.
I know that buckeye cleverly add this functionality to its builds by a multi color led.
Anyone knows Boxem also has this?

 

[imdamo]

You are right I was off-topic..

But I have (a Boxem) question:
The purify modules have an i2c interface that allows for detecting of clipping in the voltage and current domain.
I know that buckeye cleverly add this functionality to its builds by a multi color led.
Anyone knows Boxem also has this?

I don't know anything about that. But it does remind me of another question I had regarding this amplifier, since they are mentioned in the same sentence on Boxems website.

"Arthur 4215/E2 input buffer board was designed in-house. The challenge has been to fit in a relatively limited space the buffer circuits for two channels, the gain management switch, the audio sense circuit, the I2C bus communication with the amplifiers and finally the supplies for analog and digital circuits, all this while obtaining the performance at the same level as the amplification modules."

My question is: What digital circuit? I thought this amplifier was all analogue?

Hopefully Fred will swing by at some point and clarify

 

[MCH]

I don't know anything about that. But it does remind me of another question I had regarding this amplifier, since they are mentioned in the same sentence on Boxems website.

"Arthur 4215/E2 input buffer board was designed in-house. The challenge has been to fit in a relatively limited space the buffer circuits for two channels, the gain management switch, the audio sense circuit, the I2C bus communication with the amplifiers and finally the supplies for analog and digital circuits, all this while obtaining the performance at the same level as the amplification modules."

My question is: What digital circuit? I thought this amplifier was all analogue?

Hopefully Fred will swing by at some point and clarify

I2c is a digital communication protocol. Probably the amp sends some information via i2c (as @Hayabusa mentions just above, clipping events or whatever) to a microcontroller to shine a led or take whatever action. Probably the audio sense function goes through the microcontroller as well. I imagine that all this, and maybe some other things going on under the hood, is what is referred to as the digital circuit.

 

[imdamo]

I2c is a digital communication protocol. Probably the amp sends some information via i2c (as @Hayabusa mentions just above, clipping events or whatever) to a microcontroller to shine a led or take whatever action. Probably the audio sense function goes through the microcontroller as well. I imagine that all this, and maybe some other things going on under the hood, is what is referred to as the digital circuit.

So the amp has some level of ADC on board to send status messages? That's neat.

 

[MCH]

So the amp has some level of ADC on board to send status messages? That's neat.

I have no idea, but in principle I don't see the need for an ADC. Sometimes is enough with an analog circuit to bring high or low a pin of the microcontroller.
Example: if you are curious how an audio sense circuit works (probably the one in the Boxem is more sophisticated), see here:

Audio Sense schematic needed

Hi, I am considering building a power amplifier and want it to have audio sense. I have searched a while, but could not find any solution suitable for my project. I do know Rod Elliot's Signal detecting circuit but this is a fully analog circuit that does not fit my needs...

www.audiosciencereview.com

 

[imdamo]

I have no idea, but in principle I don't see the need for an ADC. Sometimes is enough with an analog circuit to bring high or low a pin of the microcontroller.
Example: if you are curious how an audio sense circuit works (probably the one in the Boxem is more sophisticated), see here:

Audio Sense schematic needed

Hi, I am considering building a power amplifier and want it to have audio sense. I have searched a while, but could not find any solution suitable for my project. I do know Rod Elliot's Signal detecting circuit but this is a fully analog circuit that does not fit my needs...

www.audiosciencereview.com

That's really cool, but I wouldn't call that a digital circuit?

 

[Hayabusa]

I don't know anything about that. But it does remind me of another question I had regarding this amplifier, since they are mentioned in the same sentence on Boxems website.

"Arthur 4215/E2 input buffer board was designed in-house. The challenge has been to fit in a relatively limited space the buffer circuits for two channels, the gain management switch, the audio sense circuit, the I2C bus communication with the amplifiers and finally the supplies for analog and digital circuits, all this while obtaining the performance at the same level as the amplification modules."

My question is: What digital circuit? I thought this amplifier was all analogue?

Hopefully Fred will swing by at some point and clarify

The Purifi module has a microcontroller on board to check all kind of things.
It monitors temperature/voltages/currents, and must have one or more adc's

 

[amper42]

Boxem Arthur 4215/E2 arrived recently. It offers a nice looking external chassis. The package was double boxed and DHL took good care of it. DHL is an amazing service. Delivering the unit to the United States within 48 hours of shipping from Luxembourg at about the same shipping cost as an 8 pound package via Fedex within the USA. I was impressed.

The chassis is 8 7/8" wide by 11 1/8" deep by 3 1/8" tall (binding posts excluded). This Stereo PURIFI 1ET400A based chassis design is the smallest by volume when compared against the March Audio P452 or the Buckeye 1ET400A amps. On a looks basis, the rounded aluminum March Audio case is a bit more visually appealing but the Boxem case is a big step up from the bare bones Buckeye Purifi chassis. The Arthur 4215/E2 chassis design reminds me a little bit of a high quality hard drive case from the 1990's when hard drives were all 5.25" in size. The finish is a matte dark gray with a slight texture on the sides while the front panel is jet black. Once out of the box, the chassis weighs 6 lbs 9 ounces. For its size, the 4215/E2 has a feeling of weight. It doesn't come with a USA type power cord so I found a nice one in my box of spare power cords.

A 3-way toggle gain switch is available on the back. It supports 12.8, 20.8 and 27.2dB gain settings. The switch is located beneath the high quality ETI binding posts. After trying all three gain positions with the RME ADI-2 DAC FS, I settled on the medium setting which offers 73dB volume levels with the Revel F328Be speakers when the ADI-2 volume setting is at 19.5. Fred at Boxem Audio is flexible with amp builds which allowed me to upgrade to the ETI KRYO Silver Plated Tellurium Copper binding posts. (https://eti-research.com/kryo-connectors/) These binding posts are finely crafted and a joy to use with my silver Viborg VB401S Banana Plugs.

According to Kill-a-watt, the Boxem Arthur 4215/E2 uses 14W while idle. Even with the RME ADI-2 DAC FS set at 19.5 using the middle Boxem gain setting of 20.8dB, the reading never exceed 14W while the F328Be speakers were playing at 73dB levels in a large room. The Purifi design offers the best power efficiency I have tested for an amp in this class. (Compare that to the NCx500 model 5519/N2 which idles at 26W). Boxem takes it even further with circuitry on board that reduces power use after approximately 9 minutes of inactivity from 14W idle to 0.5W in standby mode. Once music is detected on the XLR input "B" the amp turns back on within approx. 3 seconds. If you don't typically turn the amp off when not playing music, this is a nice feature to limit phantom power consumption.

The Boxem Arthur 4215/E2 design incorporates Texas Instruments OPA1656 Burr-Brown op amps designed specifically for uses where audio fidelity is crucial. https://www.ti.com/lit/ds/symlink/opa1656.pdf?ts=1712286380724&ref_url=https%3A%2F%2Fwww.mouser.com%2F
In a recent Bruno Putzeys video interview he shared a preference for the OPA1656 with the Purifi amp. This was interesting as both the March Audio and the Buckeye Purifi amps were being built with the OPA1612. One difference between the 1612 vs 1656 is the 1656 has higher output current availability. While technically the 1612 should be powerful enough to drive the Purifi modules, it does appear to be pushing pretty close to its maximum levels for output voltage (considering +/- 12 VDC rails). Perhaps the greater headroom of the OPA1656 could be responsible for a subjectively better sound quality alluded to by Bruno? I still need to spend time with the Boxem 4215/E2 before I can consider whether I have a preference between the OPA1656 vs OPA1612.

Thank you Fred for all of your hard work. I appreciate your attention to detail and the quality amp builds you are producing at Boxem.

 

[n00brx]

So nice you can upgrade your binding post
Should have know this we can do it

 

[amper42]

See video at 33:01 for Discussion on OPA1612 vs OPA1656 with Bruno.

 

[imdamo]

If anyone wants to dim the LED on this thing, I put one of these little semi-transparent stickers over the LED:

Light Dimming Stickers for Electronic Displays

LightDims are light reducing stickers for electronic devices, screens and LED lights.

www.sleepsolutions.com.au

The black sticker completely disappears on the black face-plate and I'm left with an LED that's about 25% as bright as it was.
Perfect solution in my opinion.

 

[amper42]

The light on the Boxem isn't too bad. I used a small piece of black tape to reduce it to barely visible. The blue light on my Buckeye amp was about 3x brighter. A tiny piece of black tape fixed it too. If you don't want to pay $10 for special dimming stickers a tiny piece of black electrical tape will do the trick and I don't even notice it on the finish.

 

[whislai]

Just got my boXem audio Arthur 4215/E2, first impression is clean detailed transparent neutral sound, thought that it lack of color might not everybody's cup of tea, nevertheless I do think that it perform well in scientific score.

 

[whislai]

Ok further impressions on the amp, after few weeks of critical listening I starting to like this amp, especially when pairing with the S.M.S.L SU-1 DAC the sound I hear is on another level of details, even my Wharefedale Denton 80 never sounded so crisp, I'm not going to complain just because it sounded a bit bright on some recordings, I gain experience in a new way, yes sure you will hit listening fatique if you listen to some poorer recording with higher noise and less than perfect mastering. Another thing I noticed is watching movie is on a whole new level of experience because of accurate sound reproduction. I can't compare with the NAD M22 power amp since I sold it, but then judging from my memory for volume loudness level the power output should be roughly the same, include tax it's cheaper than the NAD, and also smaller, temperature wise it run just slightly hot but ok. I dunno suddenly I feel like I'm listening like a super critical musician/audiophile (which is ok) instead of casual daily listener, next I will try with some cheap preamps from AliExpress, one coming would be the Accuphase C3850 clone.

 

[amper42]

Ok further impressions on the amp, after few weeks of critical listening I starting to like this amp, especially when pairing with the S.M.S.L SU-1 DAC the sound I hear is on another level of details, even my Wharefedale Denton 80 never sounded so crisp, I'm not going to complain just because it sounded a bit bright on some recordings, I gain experience in a new way, yes sure you will hit listening fatique if you listen to some poorer recording with higher noise and less than perfect mastering. Another thing I noticed is watching movie is on a whole new level of experience because of accurate sound reproduction. I can't compare with the NAD M22 power amp since I sold it, but then judging from my memory for volume loudness level the power output should be roughly the same, include tax it's cheaper than the NAD, and also smaller, temperature wise it run just slightly hot but ok. I dunno suddenly I feel like I'm listening like a super critical musician/audiophile (which is ok) instead of casual daily listener, next I will try with some cheap preamps from Aliexpress, one coming would be the Accuphase C3850 clone.

My Boxem Arthur 4215/E2 runs cool as a cucumber in the fridge. It never gets hot even after hours of use. Is it possible you have NCx500 components inside the case instead? Or maybe the build design is different mounting the Purifi module to the top case?

 

[boXem]

Is it possible you have NCx500 components inside the case instead?

Case is not ready for screwing an NCx500 inside and since the modules are firmware controlled, they would not even start .

 

[amper42]

Case is not ready for screwing an NCx500 inside and since the modules are firmware controlled, they would not even start .

Fred - have you ever seen an Arthur 4215/E2 run hot? I can't imagine how I would get mine to run anywhere near as hot as my Denon 4700 or my Buckeye NC502MP amps. With two Revel F328Be powered through RME ADI-2 DAC FS to Arthur 4215/E2 I can barely get the amp above room temp.

 

[whislai]

My Boxem Arthur 4215/E2 runs cool as a cucumber in the fridge. It never gets hot even after hours of use. Is it possible you have NCx500 components inside the case instead? Or maybe the build design is different mounting the Purifi module to the top case?

Nope, I'm in Malaysia, I open aircond just slightly cool, not sure that's the reason, actually it's not hot until boiling egg like my Class D Audio SDS-470C, which I open the case and put few coins on the heat sink, the boXem amp just not cool, just a bit of heat, perhaps rougly less than 50 degree celcius if on high power load which sometimes I did crank for some music:

 

[Bobesku]

Ok further impressions on the amp, after few weeks of critical listening I starting to like this amp, especially when pairing with the S.M.S.L SU-1 DAC the sound I hear is on another level of details, even my Wharefedale Denton 80 never sounded so crisp, I'm not going to complain just because it sounded a bit bright on some recordings, I gain experience in a new way, yes sure you will hit listening fatique if you listen to some poorer recording with higher noise and less than perfect mastering. Another thing I noticed is watching movie is on a whole new level of experience because of accurate sound reproduction. I can't compare with the NAD M22 power amp since I sold it, but then judging from my memory for volume loudness level the power output should be roughly the same, include tax it's cheaper than the NAD, and also smaller, temperature wise it run just slightly hot but ok. I dunno suddenly I feel like I'm listening like a super critical musician/audiophile (which is ok) instead of casual daily listener, next I will try with some cheap preamps from AliExpress, one coming would be the Accuphase C3850 clone.

My BOXEM amp runs cool as well. Even after a 6-8 ours party with hard electronic music and a VERY loud volume, it was just warm. Not hot.
Maybe yours is in an enclosed cabinet? Maybe check your connections -some stray wires touching themselves? Or you are really listening at EPIC levels?

 

[whislai]

My BOXEM amp runs cool as well. Even after a 6-8 ours party with hard electronic music and a VERY loud volume, it was just warm. Not hot.
Maybe yours is in an enclosed cabinet? Maybe check your connections -some stray wires touching themselves? Or you are really listening at EPIC levels?

Yeah it's warm, not really that hot, quite amazing the efficiency of this Purifi board