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Old 05-11-2018, 08:11 PM   #2
wwenze
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Part 1: Analog performance

Outputting at ~1.90Vrms

Unloaded
20Hz THD=0.0016% THD+N=0.029%
1kHz THD=0.00021% THD+N=0.00063%
10kHz THD=0.00083% THD+N=0.0011%

33 ohm resistive load on both channels
20Hz THD=0.0019% THD+N=0.029%
1kHz THD=0.00090% THD+N=0.0012%
10kHz THD=0.0014% THD+N=0.0017%

Output impedance
Around ~0.4 ohm @ 1.9Vrms 33 ohm, limited by Arta reporting down to only 0.1dB precision

I'll just take the result as less than 1 ohm, I'm sure other reviewers with their own websites and stuff and their audio analyzers can get a more accurate number.

RMAA summary


The noise numbers look a bit weird, the spectrum shows some weirdness which does not happen with Arta. Comparing the Arta spectrums, it is around 5dB worse than my Xonar DX, so it should still be getting -105dB or better.

Of course, having the same noise level as a computer soundcard is not a good thing for an earphone amplifier, because computers are meant to be connected to speakers with volume controls, while earphones are sensitive and connected to the output of the, erm, earphone amplifier, which means noise levels need to be way lower. Somebody once said the more meaningful measurement of noise is in terms of volts. But what if this amp also has a digital volume control inside? That can change the amount of noise in terms of volts. Noise is not easy to quantify (hence why sometimes you can hear noise coming from a system that supposedly has -80dB or -100dB or better noise), and I'm feeling lazy. We shall see.

Results discussion
The numbers are unbelievable, but the graph checks out: A tiny bit of 3rd harmonic poking slightly above -120dB line.

One thing I noticed and remembered is that Arta and RMAA give slightly different numbers. And this is why I keep both measurements - Arta for the RMAA haters, and RMAA for comparison with other RMAA users.

I forgot I was supposed to use 16 ohm, not 33 ohm. But since I already did that might as well. I still have to collect max output power data anyway.

Back to the SXFi, unbelievable numbers. I didn't know my Xonar STX can measure this low, and because of this these numbers may actually be the limit of the measuring soundcard and not the SXFi.

The goal is to verify Creative's claim of THD+N=0.00036% IMD=0.0022% and crosstalk=-75dB and so far it seems to check out. I give an allowance of up to 6dB, if my numbers are worse than the claims (as is usually the case) it can be due to settings and equipment. Especially when THD+N of 0.0006% is the lowest that I have actually seen from Xonar STX self-loopback.

-75dB crosstalk without load is however pretty mediocre. Let's hope it is due to the cables/connectors/adapters, there is still chance for measurements. I have a feeling that this is the actual unloaded specs however. In which case it is really really bad, I mean because lots of cheap stuff can do at least this good with load.

I'm going to assume the SXFi should hit all the claimed specs. These are amazing numbers. The amp is amazing too, taking just a minor hit in performance from a 33 ohm load at slightly over 100mW in output power. LG has a smartphone that can hit the same number, but it doesn't have as much output power. This level of performance can win many desktop setups, and is packed into the tiniest package possible. Poor crosstalk requires further investigation, would be interesting to check if it is power supply related.

Update 7/11/18
Nope, crosstalk is this bad. And this setup using a Windows 10 tablet running on battery as the source for SXFi is the best setup out of the 3 tested - The other two being using a smartphone and my computer which also houses the Xonar STX and consequently having lots of common-mode noise. All measurement numbers - THD, noise, crosstalk, the Windows 10 tablet is better than the rest.

There is something interesting about the noise floor, or rather, the dynamic range. Well, normally SNR and dynamic range are around the same, but in some cases they can differ. And SXFi is one case.

Yellow is Honor 8 Pro's 3.5mm out at max volume

Spoiler!

The higher the amp volume, the higher the noise floor. Also, if your Android volume is low but the amp volume is still high, the noise floor remains high. So you should always keep the Android volume max while reducing the amp volume.

This happens when Android volume has been lowered somewhat but amp volume is still max:
Spoiler!

So, at typical listening volumes, the SXFi noise level is comparable to Honor 8 Pro. At higher volumes, the smartphone cannot reach that high so not a comparison. And it does still keep the THD+N performance I can't fault it.

But what I will say is, this noise level is typical; while not bad, it is also not good enough to spend money on if your goal is lower noise. It is comparable to smartphones, so if that is enough for you, then SXFi is enough for you. However, other amps using mechanical volume control can attenuate both the signal and the noise.

With most of the measurements finalized, I can give it a judgement proper:

Results discussion
- Distortion values are still out of this world.
- Noise is... not exactly what I expected from a USD$150 product. Acceptable, but can do better.
- Crosstalk is really, really, really, really, really bad. -75dB is probably the absolute best case scenario - No load, good power, good source. Drops to around -50dB best case with 33 ohm load regardless of output volume, and around -45dB with 16 ohm load. If your source is bad, these values can get even worse.
- Output power / behavior with load, the problem is output power depends on load impedance, and crosstalk also depends on load impedance, I cannot say that the amp is not affected by high output power. Also, Creative's output power ratings seem to be peak values as opposed to RMS values. Also, I can only get around 292mW with 16 ohm load before the amp starts becoming unstable. While this is still pretty respectable, I am conflicted on whether I should score against not performing up to rated specs.

- The problem is that despite the excellent distortion and reasonable noise performance, crosstalk is really, really horrible, and you're going to hear -75dB or -50dB way earlier than -100dB or -110dB. And we are dealing with a technology that requires careful cross-feeding of different channels' sounds at different phases, I believe this requires a crosstalk performance that is top-notch. If you don't need the SXFi, it is very hard to recommend this product as an amplifier, just due to the crosstalk alone.

Verdict (combining parts 1 to 4)
Between the flawed analog performance, flawed SXFi effect, and the unreliable performance (clipping or "static") appearing sporadically, it is *very hard* to recommend getting this.

If the analog performance was good, it would have been a good reason to get this amp even if you don't need the SXFi effect. But due to the crosstalk, it cannot be called good. Unless you don't mind living with high crosstalk for some reason.

If you are thinking of getting it for the SXFi effect, try HeSuVi with Out Of Your Head Genelec Studio virtualization. If you can tolerate that and you want something that is 2 to 3 times more aggressive, get the SXFi.
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Last edited by wwenze; 08-11-2018 at 12:00 AM..
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