The Fiio KA15 is a portable USB DAC/headphone amplifier recently released (Fall 2024) by Fiio. Key features are:
- High output power: 560 mW per channel into 32 Ohm (in balanced desktop mode)
- Dual CS43198 (DAC chips) + SGM8262 (op-amps)
- 10-band on-device parametric EQ
- Not a dongle-type yet compact form factor
Measurement Setup
- AD converter: E1DA Cosmos ADCiso Grade A in Mono Mode, and Cosmos Scaler as a buffer.
- Analog preamp: E1DA Cosmos APU for 1 kHz SINAD and low-level tests.
- Software: Room EQ Wizard (v5.4 beta 80) for most of the tests, and Paul Kane's Multitone Loopback Analyzer (v1.2.9).
- Some test results were compared to the performance of the JCALLY JM20 and JM20 MAX whose measurements were made in exactly the same setup.
- Unless otherwise noted, the device's balanced outputs were measured in its Desktop and Class AB mode.
Results
Starting with a 1 kHz sinusoidal test of its balanced outputs under no load (20 kOhms):
This is on par with a desktop device's performance.
Another 1 kHz sinusoidal test of its unbalanced outputs under no load (10 kOhms):
Excellent performance. Only a slight decrease in SINAD due to weaker fundamental tones.
Low-level, 50 mV output performance:
As expected, for the same 50 mV level, its unbalanced output has a lower noise floor.
It provides choices of LP filters:
Frequency response (w/ Fast-PC filter) is as expected:
Jitter test:
Jitter suppression is not perfect, but these small errors should not be audible.
Multitone test:
SMPTE IMD measurements versus output levels:
The IMD results of the three devices shown---Fiio KA15, JCally JM20 and JM20 MAX---are essentially the same as each other, except small differences near their maximum output levels. In particular, the JM20's IMD rises near the max output under this 300 Ohm load because its headphone driver integrated into CS43131 has lower current capability than the other two devices' separate op-amps.
THD+N versus frequency:
Nothing to be concerned about.
Output power of its unbalanced output:
Its unbalanced outputs are as powerful as many similar devices' balanced outputs!
Let's see its balanced output power:
Output power from this small device is incredible. This is the record-shattering, highest-output portable USB DAC/headphone amp among the devices tested at ASR so far.
In case you want to see the same results on the output voltage scale:
(Output impedance measurements of both balanced and unbalanced outputs will be posted when I get a chance to measure.)
All the measurements reported above indicate excellent, if not state-of-the art, performance of the KA15. In particular, its measured output power is unbelievable. However, the story does not end here.
There is something very interesting that is not found by the standard package of measurements. We saw the results of a 32-tone test earlier, which was performed at the maximum unclipped signal level. Normally, if we feed the same signal at a lower level, the ratio of the signal to distortion/noise deteriorates only slightly because of the weaker signal. For some CS43131- and CS43198-based devices, this is not the case---see here for more information.
Unfortunately, the FIIO KA15 turns out to be one of the devices producing elevated noise and distortion when fed with multitone signals at lower levels. See below for normal FFT results of 32-tone signals at high levels:
These are great results.
But as the signal gets weaker, we get the following problematic responses:
Yes, for a very wide range of signal strengths, we get quite nasty responses, losing several bits of resolution!
The response becomes normal when the signal reaches a much lower level:
To see the entire picture, a sweep of 32-tone tests across a range of signal strengths was performed:
Notice a huge "hump" which indicates the rise of total distortion + noise in a range of signal strengths. This may be dubbed a "Cirrus hump." In comparison, the JCALLY JM20 and JM20 MAX do not show this behavior in the same measurements.
One may think this measurement condition, made of 32 equal-amplitude tones, is unrealistic which may never occur in real audio contents. In fact, these signal processing defects can be found with any multitone signals, even with dual tones, as long as tone components are in similar amplitude. See below:
This dual-tone signal, called "TDFD Bass" in Room EQ Wizard, is simply composed of 41 Hz and 89 Hz sine tones. As with multitone signals, the KA15 distorts in a wide range of signal strengths. Again, to see the big picture, a sweep of these dual-tone (TDFD Bass) IMD tests across a range of signal strengths was performed:
Conclusion
So, what can we say? It is still difficult to tell how clearly audible these measured distortions would be in reality. Of course, it should depend on audio content. But given the fact that this problem is observed even in a simple dual-tone test reported above, it is no wonder Roman at RAA was able to easily spot a movie soundtrack to demonstrate the distortion. Obviously this is an engineering flaw that should not occur in a DA converter targeted at Hi-Fi markets and consumers.
The FIIO KA15 would have been an ideal recipe for a portable USB DAC/HP amp for those looking for high output power and hardware parametric EQ in a small form factor. Only if it had been implemented properly. In its current implementation, I cannot recommend it. In fact, I am in the process of testing quite a few CS431xx-based devices, some of which are mine and others were sent by an ASR member. Eleven of them in total! Unfortunately, except for a few dongles (including the JCALLY JM20 and JM20 MAX), most of them exhibit this problematic behavior. Based on these observations, like Roman at RAA I also believe it can be resolved by firmware design. But the problem is that there is no clear register in the chips' datasheets that must be related to this behavior. No one knows for certain, perhaps except for Cirrus Logic engineers (or even worse, former Wolfson engineers). I am planning to write another special review on this issue, covering these CS431xx-based devices..
Other Remarks:
- The distortion behavior is not affected by the Class H or Class AB mode in the firmware setting.
- The distortion occurs under any impedance load.
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I got a Topping G5 which is stellar but big, heavy and no hardware EQ.
