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:
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:
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:
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:
Dynamic range was not as bad but still, not remotely what it should be in this class product:
There was a lot of interference in jitter test:
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:
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:
Frequency response was excellent:
While not state of the art, signal to noise ratio was very good as well:
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:
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:
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.
Signal to noise degraded as well:
50 millivolt SNR is very poor in general let alone for a device this expensive:
Let's see what it can do into 300 ohm load:
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:
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:
Frequency response was also a bit more rolled off:
Channel matching is not good but there is a balance control which you can use to partially compensate for this:
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/
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:
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:
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:
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:
Dynamic range was not as bad but still, not remotely what it should be in this class product:
There was a lot of interference in jitter test:
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:
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:
Frequency response was excellent:
While not state of the art, signal to noise ratio was very good as well:
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:
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:
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.
Signal to noise degraded as well:
50 millivolt SNR is very poor in general let alone for a device this expensive:
Let's see what it can do into 300 ohm load:
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:
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:
Frequency response was also a bit more rolled off:
Channel matching is not good but there is a balance control which you can use to partially compensate for this:
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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