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Old 07-11-2018, 01:08 PM   #8
jasonhanjk
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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.
300 ohm headphone able get 12mW power.
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