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Geshelli Archel2.5 Pro Review (headphone amplifier)

amirm

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This is a review and detailed measurements of the Geshelli Archel2.5 Pro headphone amplifier with XLR balanced inputs (no output). It was kindly sent to me for testing by a member a while ago :). It costs US $180 from the company.

The Archel2.5 Pro is typical of Geshelli enclosure with aluminum and plexiglass:

Gehselli ARCHEL2.5 PRO Review Headphone Amplifier.jpg


The ones on the website seem to have smoked glass now which I think is a better bet. Wish there was a 3.5mm jack since there seems to be room for it. Controls are microprocessor based requiring long press to change the gain on the input selector.

The back panel is nothing unusual other than aforementioned inclusion of XLR inputs:

Gehselli ARCHEL2.5 PRO Review XLR back panel Headphone Amplifier.jpg


Forgot to take a picture of the external power supply but it is very small, not a whole lot bigger than a phone charger. That aspect is nice but the small size also means lower current delivery which can hurt driving low impedance headphones.

Archel2.5 Pro Measurements
I exclusively used the XLR input on this unit. With 4 volts in and 4 volts out, this is what we get:

Gehselli ARCHEL2.5 PRO Measurements Headphone Amplifier.png


That is pretty good, just shy of top of the class:
best headphone amplifier review xlr.png


If I turned up the volume a bit more with output at 4.3, SINAD would jump to 120. Alas, that would not be fair to other companies so left it there.

Signal to noise ratio is excellent as well with the same 4 volt out:

Gehselli ARCHEL2.5 PRO Measurements SNR Headphone Amplifier.png


Turning the volume down to 50 mv (right), gives us almost top of the class rating again:

most quiet heapphone amp review.png

So you should be good with your sensitive IEMs.

Frequency response is of course ruler flat:
Gehselli ARCHEL2.5 PRO Measurements Frequency Response Headphone Amplifier.png


Most important test is power vs distortion+noise so let's get into that starting with 300 ohm load:

Gehselli ARCHEL2.5 PRO Measurements Power into 300 ohm Headphone Amplifier.png


Low gain performance is superb. Alas when you switch to high gain, you loose some of that. Power is healthy at 152 milliwatts before clipping.

Switching to much lower load of 33 ohm shows the issue I talked about regarding lack of current:
Gehselli ARCHEL2.5 PRO Measurements Power into 33 ohm Headphone Amplifier.png


Low gain is once more excellent as far as noise and performance but that better be all the power you need (half a watt). Switching to high gain gets you a bit more power but with more distortion and then severe clipping.

Channel matching is a bit worse than I expected with some imbalance early in the range which I don't often see:

Gehselli ARCHEL2.5 PRO Measurements channel balance Headphone Amplifier.png


As noted though, with all these analog controls what you get may very well be different than what I have/have measured. Still, be on guard with issues regarding very sensitive IEMs.

Geshelli Archtel2.5 Pro Listening Tests
I started testing using the Sennheiser HD-650 headphone. Even in low gain there was plenty of power to produce absolutely clean and dynamic response. Absolutely superb. Switching to high gain though took things to an entirely different level. For the few seconds that I dared to turn up the level to near max, my skull resonated so much (and with such great fidelity) that I think it may have jumbled some of my brain cells, converting me from an engineer to a painter!!!

I then switched to my very inefficient, 25 ohm Ether CX headphone. Up to pretty reasonable volumes the fidelity was excellent. Turned up the volume a bit more and bass notes started to have pops of static. Go a bit more and incredible transformation happens with bass notes getting modulated into some kind of electronicky synthesized tones! It was uncanny as at first I thought it was in the music only realizing that it is not. Again, there was enough volume before this happened but there is a hard limit here as indicated by the 33 ohm measurement above.

Conclusions
The Geshelli Archel2.5 Pro definitely belongs to the new elite class of headphone amplifiers which provide incredible amount of power and transparency at the same time. You are guaranteed to hear what is in the recording, no ifs and buts. For Archtel2.5 this is true of high impedance headphones. With low impedance headphones, you give up some power which the competitors do not. So be mindful of that as you shop.

Overall, I can recommend the Archel2.5 Pro for medium to high impedance headphones.

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bigjacko

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Thank you for the review Amir! One thing I don't understand is why the SINAD is only -116dB when distortion are around -130 and the signal to noise ratio is -124dB? I thought the SINAD should be noise limited, so must be -124dB.
 

NightlyNurse

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Awesome review. Can't wait to see the day you check out the Geshelli Erish or the Geshelli Jnog
 

PeteL

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Forgot to take a picture of the external power supply but it is very small, not a whole lot bigger than a phone charger. That aspect is nice but the small size also means lower current delivery which can hurt driving low impedance headphones.
Just out of curiosity, lower means how low? Do they spec the Amp delivery of this PSU and do you think that just swapping to a more powerful 12V PSU is all needed to solve this? To me it says great circuitry, with some oddities, but most of these seam to say "need more current". Along maybe some penny pinching on the pot.
 
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amirm

amirm

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Thank you for the review Amir! One thing I don't understand is why the SINAD is only -116dB when distortion are around -130 and the signal to noise ratio is -124dB? I thought the SINAD should be noise limited, so must be -124dB.
Good question. Partial answer is that the bandwidth for SNR measurement is limited to 20 kHz whereas the dashboard uses 22.4 khz. So there can be more noise between 20 and 22.4 kHz.

On distortion, there are two spikes with one at -129 and another at -130. These two add up to -126 dB or so, not 130. Summing 126 and 124 will get us down to 121 SINAD. Still higher than I showed. When I get a chance I will measure again.
 
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amirm

amirm

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Just out of curiosity, lower means how low? Do they spec the Amp delivery of this PSU and do you think that just swapping to a more powerful 12V PSU is all needed to solve this?
It may help some but it is possible the internal design can't dissipate more power.
 
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amirm

amirm

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Will you be measuring RCA input and multi-tone THD+N?
Left to myself, no. :) It is likely to be similar performance. I think the point of this device is for people who need the XLR input. Otherwise they have other amps without it.
 
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amirm

amirm

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How come the sinad is quite a bit lower than the archel 2 pro?
It has a slightly different gain structure due to XLR input. As I noted in the review, if I just turn up the volume a hair it just to 120 dB SINAD. Other than that, they have to explain, not me. :)
 

digicidal

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A real engineer will not make plexiglass chassis.
I have no idea what your qualification of "real" is... but I would disagree with this strongly. Perhaps you meant to say a real marketing executive would not make such a chassis? Clearly (pun intended) the use of acrylic is not a significant detriment to performance - which is all most engineers would actually care about. That being said, I do agree with you on not being a fan of the aesthetics... but it clearly performs perfectly fine, and I'd rather the BOM budget get spent inside than outside personally.
 

Degru

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Do you have a multitone/distortion sweep measurement to see if it has the same rising distortion in bass that the 2 does?

Also, what is the polarity like when using the XLR inputs? I found that my unit produced flipped polarity when running through XLR. Not audibly problematic, but weird nonetheless. Geno said it's because the XLR input was deriving signal from the cold side rather than the hot, and will be fixed in future version.

Interestingly mine had 3.8Vrms out at full volume low gain. (I checked and my DAC was putting out 4V). Hopefully that will be resolved after my unit goes through RMA for a different issue.

I use mine as a preamp for my Stax setup, because I need something with a properly clean single-ended output that takes a balanced input from my Modius, but not necessarily high power output. This fits the bill for not too much money, the alternative being a DIY transformer-based passive solution (and transformers usually aren't a good thing to have in the signal path)

There will likely be a revised version coming sometime soon since they updated the Archel 2, which will probably have a better volume pot at the very least. So I'd suggest waiting for that to come out for anyone considering. However for actually driving headphones, I find the Heresy is quite a bit more capable as long as you don't require XLR inputs.
 
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Francis Vaughan

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I have no idea what your qualification of "real" is... but I would disagree with this strongly. Perhaps you meant to say a real marketing executive would not make such a chassis?
Actually, I suspect there is an entire class of nerd engineer that thinks plexiglass is cool. Aesthetic sensibilities or sense of style are often incompatible with engineers. Seems more likely that the company has nobody with any clue about such things on its payroll. Box was probably designed by the same guy that designed the electronics. That rarely ends well.
Case is just an off-the-shelf extrusion, and looks very hobby level. The company would do well to invest in tooling for a better look.
 
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