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SPL Phonitor X Review (DAC & Headphone Amp)

amirm

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#1
This is a review and detailed measurements of the SPL Phonitor X DAC and balanced headphone amplifier. It was kindly purchased refurbished by a member and drop shipped to me. There was a label on the unit saying it was certified back in 2019. It has some fine scratches so it was definitely used.

EDIT: New it costs US $2,500.

EDIT 2: I didn't realize there are hidden dip switches underneath the unit to set the gain. The setting was the high gain for all the measurements you see below.

I must say, I have been lusting after the Phonitor X from the first time I saw it at an audio show:

Phonitor X SPL Review balanced headphone amplifier and DAC.jpg


Aren't those VU meters gorgeous? What is that? You can't read the labels? I could not either! You literally need a flashlight or desk lamp to see them. Gray type on red just doesn't work from contrast point of view.

From the back you see that there is a ton of connectivity and functionality provided:
Phonitor X SPL Review balanced headphone amplifier and DAC back panel.jpg


You can see the DAC/digital inputs on the right. Alas, in the 15 minutes I had before lost my patience, I could not get the USB port to work. Windows would recognize it but I could not get audio. It could be pilot error but I tried a lot of things and it would just not produce sound. So I did my DAC testing using Toslink input.

As regular readers know, my focus here is on engineering and performance. As such, I am ignoring the functionality and value of crossfeed, etc. that this unit has.

Claim to fame of the unit is that it uses discrete amplifiers in order to be able to operate at a very high voltage of ± 60 volts. They say that brings very high dynamic range which it can do. But let's find out if there is a down side to this...

SPL Phonitor X DAC Measurements
I must say it was a huge let down to be greeted to this level of performance from the DAC subsystem:
Phonitor X SPL Measurements DAC.png


best DAC and headphone amplifier 2021 review.png


On top of that, max volume was only 2 volts instead of 4 volts. I thought maybe it does better at lower voltages but it does not:
SPL  Phonitor X Measurements DAC THD+N vs Level.png


Dynamic range was not as bad but still, not remotely what it should be in this class product:
SPL  Phonitor X Measurements DAC Dynamic Range.png


There was a lot of interference in jitter test:
SPL  Phonitor X Measurements DAC jitter.png


I went ahead and tested for jitter rejection by programming my Audio Precision analyzer to induce 1 nanosecond of jitter at 1 KHz. Sadly there was no rejection of it:

SPL  Phonitor X Measurements DAC jitter induced.png


So best to use a clean digital source if you are going to use Toslink input.

Let's move on before we get more depressed over the DAC functionality...

SPL Phonitor X Pre-amplifier Measurements
For this test, I used XLR input and XLR Output in the back. I fed the unit 4 volt and adjusted the volume control for 4 volts. Was disappointed to see the VU meter peg to the max with no range switch to avoid that. Anyway, performance here was quite uplifting relative to the DAC:

SPL  Phonitor X Measurements preamplifier.png


Frequency response was excellent:
SPL  Phonitor X Measurements preamplifier frequency response.png


While not state of the art, signal to noise ratio was very good as well:
SPL  Phonitor X Measurements SNR preamplifier.png


I was hoping to finish this set of tests on a high note but was not meant to be when I saw the poor crosstalk performance:
SPL  Phonitor X Measurements preamplifier crosstalk.png


Oh well.

SPL Phonitor X Headphone Amp Measurements
DAC and pre-amp modes were appetizers. We are here for the main meal which is the performance of the headphone output. Given the competent pre-amp performance above, I expected the same here but it was not the case:

SPL  Phonitor X Measurements headphone.png


How did we lose 10 dB of performance at 600 ohm load relative to 200 kHz ohm that is used in pre-amp test? The reason for this will become clear shortly.

best balanced headphone amplifier.png


Signal to noise degraded as well:
SPL  Phonitor X Measurements SNR headphone.png


50 millivolt SNR is very poor in general let alone for a device this expensive:
most quiet headphone amplifier.png


Let's see what it can do into 300 ohm load:

SPL  Phonitor X Measurements headphone power 300 ohm.png


Good news is incredible amount of power if you allow a lot of distortion. Before flat out clipping we have whopping 3 watts of power!

Performance drops rapidly though when we go down to a 50 ohm load:

SPL  Phonitor X Measurements headphone power 50 ohm.png


We have nothing to hang our hat on here. This amp simply doesn't low low impedance loads as we see in these series of sweeps:

SPL  Phonitor X Measurements balanced power versus load headphone.png


Frequency response was also a bit more rolled off:
SPL  Phonitor X Measurements Frequency Response headphone.png


Channel matching is not good but there is a balance control which you can use to partially compensate for this:

SPL  Phonitor X Measurements balanced channel match headphone.png


SPL Phonitor X Listening Tests
As usual I started with my Drop Ether CX low impedance headphone. The Phonitor could drive it well but it was also easy to drive it into distortion.

I happened to have an HE-6 headphone on hand. So decided to test with that as well. Same thing happened here although distortion was a bit earlier. I tested the Topping A90 with it and had similar results.

Conclusions
SPL Phonitor X is a gorgeous looking unit with its pretty VU meters and nice industrial design. Alas, its DAC is a "phoned in design" that would be suitable to a $20 ebay special than anything performant. As a pre-amplifier it functions well. As a headphone amplifier though, it is only happy with very high impedance headphones. Its high voltage amplification helps a lot here. Below that, its performance is not competitive with amplifiers at much, much lower cost.

Given the high price, I just can't recommend the SPL Phonitor X. You can do so much better these days with modern designs. Get it if you like the looks, and have high impedance headphones.

------------
As always, questions, comments, recommendations, etc. are welcome.

Appreciate any donations using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
 
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cursive

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#4
Such a cool look with the red faceplate and the pale yellow of the VU meters. Shame the performance doesn't match the physical design. I'm betting the dac is better over usb, but too many other faults for that to save it.

EDIT: HE-6, awesome! Surprised to see the A90 was also driven to distortion. Hoping that means we get to see a full review on these cans.
 

raif71

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#5
I saw this advertised locally in my country but only amp portion. The dac was not included. Inquired about it coz of the vu meters but still pricey.
 

Grotti

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#6
Thank you for the test: I also decided to buy a RME and I couldn't be happier :)

Why didn't you use your Sennheiser for the listening as you usually do? And since the graphs seem to show some mains noise (not very high though): could this be lowered to improve SINAD a little bit? Or could this be due to the high voltage the unit works with?
 

xema

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#7
I heard this one and the first generation phonitor, x is way more better than the first generation, both measurement and listening.
But, the sound is still not enough satisfying.:rolleyes:
 
OP
amirm

amirm

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Thread Starter #9
Why didn't you use your Sennheiser for the listening as you usually do?
I thought the HE-6 was a more suitable headphone to test its drive capability, not realizing its impedance is low. If I have time, will test with Sennheiser.
 

pierre

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#11
So many people wanted this thing tested, and many positing it would be phenomenal. Dont know why they would think that, seems like the typical audiophile flair over function type of company.
I had high expectations. SPL is in the pro world supposed to sell the best equipments: from EQ to compressors they are supposed to be best in class (like Maselec in the US). A 4 bands stereo EQ is around 4k$.

spl-pq.jpg
 
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kdp

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#12
I would be keen to see if SPL responds to this. There was a video on their site where a Phonitor model had "pegged" the AP525 while measuring SINAD - some 113dB+

I have a Phonitor E (which i think is sonically the same as the X) running an HD800s in balanced mode and I am fairly happy. But then again, I guess both 100dB and 113dB SINAD are below my hearing threshold / resolving threshold of my Headphones.
 

cursive

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#14
Looking at the specs on their site, an interesting thing I noticed is that @ 300ohms and 32ohms the headphone output is actually rated higher over the single ended 1/4in out, vs the balanced xlr. I don't think I've seen an amp before that's rated that way, so seems like if you're using lower impedance headphones it's better to use the 1/4 in output.

It's still only rated 1w @ 32ohms with 1%thd, so still surpassed by a lot of todays kit, including something like JDS labs Atom.
 

respice finem

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#18
Wow, expected it to be half decent, doesn't seem to be the case :facepalm:
I would still call it half decent, if it wasn't for the price... I'm curious if the manufacturer will comment on this, official specs are here (at the bottom of the page) https://spl.audio/en/spl-produkt/phonitor-x/
A second thought on this: This shows (unless we have a defective unit) that many people don't hear many flaws of their gear, so much for alleged "golden ears" :p
 

Chrispy

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#20
One thing I'd like to see tested is the resistance to surface ticks/pops thru the pre. Is there a way to do that? Could certainly make a pre more palatable if it could do that reliably while maintaining reasonable fidelity....
 
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