Part III: Topping DX9 "15th Anniversary" Limited Edition DAC & Headphone Amplifier - DSD, S/PDIF inputs, headphone out, pre-out, and AMPT. And the desire beyond Perceptibly Perfect.

With Raspberry Pi 'Touch' streamer showing album art running RoPieee, and the Topping DX9 VU meters playing, this looks quite nice in the audio rack!

Let's finish up with the last installment of the review/measurements for the Topping DX9 "15th Anniversary" DAC (see Part I, and Part II previously). As we have seen up to this point, it's quite a unique looking DAC and the initial PCM measurements over USB2.0 look great as a modern hi-resolution converter. In Part II I noted that there was an issue with the 176.4/192kHz frequency response that Topping was able to correct quickly with a firmware update. I'll be using the latest firmware 1.23 for the measurements here.

Let's continue then to dive in and explore the objective performance with some of the other main features for this DAC.

Playing "Quad-rate", DSD256 at 11.28MHz. Nice use of dual-screen set-up to show data about the digital stream.

I. DSD

Let's enter the world of DSD for a little bit.

I assume there are still a number of audiophiles listening to DSD regularly. There are many recordings out there available (for example on sale at NativeDSD.com), but as usual, be mindful of the fact that since native 1-bit DSD is not conducive to anything more than basic editing, the vast majority of DSD at some point had to be edited in multibit-PCM (like 24/352.8kHz "DXD"). Over time, I've added to the list of SACDs that appear to be just upsampled/transcoded PCM and I've seen in recent years DSD256 and DSD512 material that probably originated from hi-res PCM like 24/96 based on the Nyquist roll-off.

Here are some 1kHz THD+N measurements in DSD for your consideration compared to 24/96 PCM at the same output voltage level:

For context, have a look at this previous article on DSD and my "standard" DSD signals.

Those are good DSD 1kHz THD+N results. Using the SoX-created DSD samples with CLANS noise-shaped modulator setting, the sweet spots for DSD performance appear to be DSD128 and DSD256. Notice that as the DSD rate increases, the ultrasonic noise can be pushed further up and thus less likely to have noise energy amplified and sent to tweeters.

Bigger isn't always better as you can see with the DSD512 performance where the harmonic distortion is a bit higher for this device. As is the case with most modern hi-res DACs, there's usually nothing to worry about. Even with the higher THD+N, at DSD512 all harmonic products are still below -115dB and DSD512 playback with the limited tracks I have sounds great.

Internally, the AK4499EQ operates as a multi-bit sigma-delta device (presumably 7-bits like the AK4499EX) which is what PCM input gets converted to inside the DAC. In comparison, DSD is a noisier 1-bit sigma-delta signal that requires quite aggressive noise-shaping to achieve low noise floor within the audible frequencies. It should be no surprise I think that PCM measures better with basically every DAC I've ever measured and compared with to DSD.

Here is the 1/10-Decade Multitone 32 in DSD64 to DSD512 (click on image to zoom):

Beautiful performance across the board. By stacking the FFTs as above, we can see the change in the ultrasonic noise as we increase the DSD rate up to 96kHz. The test signal is reproduced very well for each DSD rate, with at least 119dB noise plus distortion-free range below the peak level.

While the Dunn J-Test is not designed to detect jitter with 1-bit DSD data, we can try anyways. Here's what it looks like for the Topping DX9 - 24-bit J-Test converted to DSD using SoX:

Interesting, we can see some very low level sidebands down around -140dB or less. Over the years, I've generally found minimum issues with the J-Test in DSD form.

II. S/PDIF - Coax and TosLink

Next, let's move on to an examination of the S/PDIF interface and performance. This DAC features 2 coaxial and 2 optical inputs; more than enough I think for older transports like CD spinners and streamers like the Chromecast Audio.

To start, I confirmed again that indeed the new firmware 1.23 discussed as an addendum last time fixed the frequency responses at 176.4kHz and 192kHz which are the maximum sample rates supported for S/PDIF:

Notice that the graph above is with TosLink input. In some older and lower quality DACs, the fiber optic interface might not be able to handle 192kHz. No problems here.

Numerically, let's have a peek at the RightMark results - measured from XLR out for lowest noise level comparing USB, Coax, and TosLink digital inputs:

Looks excellent all around. Notice a slight superiority of the USB2.0 input when it comes to lowest noise and the slightly lower distortion.

We can plot the 24/96 results to compare:

Most notable is the IMD+N sweep where we can make out distortion for TosLink > Coax > USB. Very tiny differences as we're talking about distortion levels below 20kHz of less than -110dB so nothing that would suggest the ability to differentiate between the digital inputs in blind listening (unblinded listeners can claim all kinds of things).

The thing with S/PDIF is that while it's a convenient unidirectional interface with billions of devices supporting it, from a strictly fidelity point of view, it transmits both the clock and data on a single line which the DAC has to lock onto and try to reject as much of the temporal variability (jitter) as possible. As a result, there is often an increase in S/PDIF jitter which we can see here:

I've been using the old Squeezebox Touch as my S/PDIF coax and TosLink streamer connected to the LMS/Lyrion music server here at home over WiFi for these kinds of tests over the years (as per the hardware picture above). For this test, I used a generic 6' RCA cable as coaxial, and inexpensive 6' glass TosLink cable. As you can see, there's a significant difference between asynchronous USB2.0 compared to the S/PDIF inputs.

While Topping advertises that the AK4118 SPDIF receiver might be the lowest jitter IC, it's clearly more jittery compared to the USB performance. Having said this, are we likely to be able to hear the difference!? No, of course not. The Dunn J-Test is intended to stimulate jitter so we can see/measure it. Real music is not like this test signal. While present, notice that the highest level sidebands are down below -120dB from the 12kHz peak. Furthermore, since jitter is worse at higher frequencies, 12kHz is an octave beyond the most sensitive audible frequencies (around 1-5kHz). Even if jitter anomalies were to show up in actual music >10kHz, it would be extremely unlikely to be noticed due to the combination of low amounts, and reduced human physiological audibility.

Between the coax and TosLink, it's quite typical to see a bit more jitter with the optical TosLink. Notice the slightly higher sidebands in the TosLink tracing.

This graph argues against old-skool audiophile reviewers who complain about the use of the USB interface because it's a computer "printer" interface. 😉 As you can see, even when just plugged into a typical Windows 11 Beelink MiniPC, jitter is better than dedicated audio S/PDIF. Furthermore, there is no evidence on the RightMark results earlier to suggest that USB is any more noisier than S/PDIF in a modern DAC with 24-bit signals.

Alas, I don't have an I2S transport so no test results for that input. Also, I don't have an AES/EBU transport easily available (I guess I could unpack my Squeezebox Transporter with AES out). And while wireless Bluetooth isn't meant for highest fidelity playback, it sounds great and I use it all the time, but as a lossy system with compression based on psychoacoustic techniques, I don't anticipate anything other than the resolution limits shown in previous testing like this. 

The six NFCA discrete headphone amplifier modules.

III. Headphone Amplifier

Let's have a quick look at the headphone output. Alas, I did not have time to measure the balanced outputs so let me just focus on the 1/4" single-ended port and see how this performs with varying low (20Ω), medium (75Ω), and high (560Ω) dummy loads.

Here it is at Lo-Gain out to 4Vrms, both channels driven:

Even with the low 20Ω load, at Lo-Gain, while 2nd and 3rd harmonics increase above 1Vrms, the amplifier has no problem achieving clip-free performance out to the maximum ~4Vrms which is 0.8W with THD <0.01%/-80dB.

And here's the Hi-Gain (+6dB) out to ~8Vrms at 0dBFS, both channels driven:

With the higher voltage output, we see clipping using the 20Ω load at 7.6Vrms or around 2.9W. Note that I used a conservative 0.1% THD distortion threshold. At the usual 1% THD+N, this would be 3.1W into 20Ω, <1% THD+N. On the graph, while I only showed THD, the THD+N level is essentially identical to the THD line above 500mV. This result is consistent with Topping's advertised 3.3W x 2 into 16Ω at <1% THD+N.

The headphone amp has no problem with supplying adequate current to drive the 75Ω and 560Ω loads to 8Vrms while keeping THD+N below 0.005%/-86dB.

Within the DAC menu, you can select Line Out, Pre Out, and Headphone Out to be turned on independently. In measurements I didn't see any significant difference whether all outputs were turned on or not. Also, reducing the number of concurrent outputs did not significantly change power utilization (stable ~15W max).

IV. Preamp Output

The pre-amp out allows this DAC to output higher voltage signals for low-gain amplifiers. The most common situation I believe is when you pair the XLR output to a device like the Benchmark AHB2 amp where peak output is achieved with input level up at +22dBu/9.75Vrms.

So, let's switch the measurement Cosmos ADC to its highest 10Vrms balanced input level and have a look at the resolution of the Topping DX9 XLR Pre-Out in Hi-Gain mode up to 10Vrms/+22.2dBu:

Looks good. We see the expected linear reduction in THD+N as output level increases. There's a little kink around 500-800mV due to what looks like a shift in the noise level (still low -90dB THD+N in that area). By 10Vrms out, THD+N is down to -120dB; great.

While I'm only measuring out to 10Vrms here, Topping's specs indicate that the pre-out can be pushed to 16.6Vrms/+26.6dBu if you ever need that higher level.

V. The AMPT

As I've done with previous DAC reviews, I've recorded a standard test sample for your listening pleasure. See the Archimago's Musical Performance Track (AMPT) discussion a few years back with sample files from other DACs you can also download and compare.

Topping DX9 "15th Anniversary" DAC AMPT (173MB)
24/96 capture through RME ADI-2 Pro ADC

I think you'll find the AMPT compares very favorably to others in terms of soundstage, dynamics, tonality, and very low noise performance.
 

VI. Conclusions

A friend recently wrote to me after seeing the images of the Topping DX9 DAC (Amazon Canada. AliExpress links here, and here, if cheaper from China) in Part I saying that this thing looks "sexy". Indeed, I do not believe I would be in "want" for any better-looking DAC! With the well-built enclosure, tempered glass see-through top panel, dual bright high-res color OLED screens, it is quite striking. When you turn on the top amber LEDs and select the classic-looking VU meters, there's a nice retro look to a device that is clearly of a modern heritage when we peek inside.

Of course, beauty isn't just skin-deep even though let's be honest, the look of luxury hardware is important! There is great "beauty" to be experienced when it comes to the high-fidelity audio. It converts digital audio data with resolution well beyond human audibility when it comes to low noise, low distortion, impeccable channel balance, flat frequency response well beyond audible frequency limits, with a good selection of filters (including NOS and intermediate phase settings). Performance of both the XLR and RCA outputs were excellent; in fact, I was quite impressed by the resolution of the RCA out compared to a few other DACs I've tested.

USB and S/PDIF (coax and TosLink-optical) inputs performed well and essentially were equivalent. Not unexpectedly, the asynchronous USB2.0 input performed better in jitter testing than S/PDIF. There are other devices that will reject jitter better, but there's nothing in the performance here I found to be of audible concern.

Beyond the basic DAC line outputs, we see excellent performance with low distortion for the pre-amp outputs as tested up to 10Vrms/+22.2dBu XLR in high-gain mode (the device is rated up to +26.6dBu if you need very high output voltage). This is great especially for some of the low-gain, very low distortion amplifiers like the Benchmark AHB2 (+22dBu for full amplitude), Topping's own LA90 Discrete (+19.5dBu sensitivity) or B200 Monoblock (+23.8dBu sensitivity) connected with XLR in. With these kinds of amps, one could achieve better than THD+N -110dB from digital in to amplifier output! No loudspeaker (or headphone) in existence would be able to reproduce that kind of resolution. Unless you need analogue/phono inputs, the Topping DX9 can be the heart of a supremely high performance digital system.

Let's of course not forget that this is also a high performance headphone amplifier at least on par if not exceeding Topping's own A90 Discrete Headphone Amp. The DX9 has 6 discrete NFCA amplifier modules that can push up to an advertised 3.3W x 2 into 16Ω <1% THD+N unbalanced, and 10W x 2 into 16Ω <1% THD+N balanced across the 3 outputs (1/4" phono single-ended, 4.4mm TRRS balanced, 4-pin XLR balanced) simultaneously. While I did not run balanced headphone out testing, I can confirm that the single-ended output into low/medium/high loads achieved excellent performance consistent with these specifications. This should be more than enough power except for the most demanding low-sensitivity headphone designs!

Honestly, I'd be quite happy if this was the last USB DAC I ever purchased. No doubt, this is an example of a Chinese audiophile manufacturer making an entry into the world of "luxury" high-end in the DAC-space with a device that's more expensive than typical, but still clearly very affordable with high value when we look around at the prices in the high-end audio Industry and compare features.

Subjectively, the AKM converters have a reputation of being "smooth" with more authoritative bass weight. While I don't necessarily agree since what I hear is simply a very good high resolution, high-fidelity sound, I've seen it often described this way.

The Topping DX9 has the makings of a "classic" product as a limited edition (~1800 units made) device based on the now-unobtainable flagship AKM AK4499EQ converter, no longer made due to the Japanese factory fire during the pandemic lockdowns. Scarce core component, beautifully applied art of industrial design, matched with high-fidelity engineering to mark Topping's 15th anniversary.

As Steve Jobs used to say: "One last thing..."

I wrote in Part II:

"With the usual 1kHz pure sine wave signal, the XLR line outs from this DAC were capable of achieving THD+N -121dB (SINAD 121dB) on my test bench quite easily. At this stage of my audio reviewing journey, whether it's actually -121dB as I measured or -124dB (see Topping advertised measurements) is immaterial for listening pleasure. 🙂"

While true, when a product performs at THD+N of -120dB already, anything beyond that is completely academic. However, for "bragging rights", it's fun to measure the limits of a device to talk about impressive engineering numbers. So with the E1DA Cosmos ADCiso (Grade A) in mono mode, utilizing the Cosmos APU, let's have one last look at THD+N/SINAD and the Dynamic Range for this device measured with the highest precision at my disposal:

One characteristic I've typically observed with AKM DACs is a nice descending "harmonic cascade" where higher order harmonics (beyond 2nd and 3rd) remain suppressed. It has been said that lower-order harmonics like 2nd and 3rd are likely inaudible and might even be "euphonic" given their prevalence in tube and vinyl reproduction to add subjective "fullness" to the sound. It's those higher order odd products like the 5th, 7th, 9th that we probably want to maintain as low as possible.

THD+N -125dB average (SINAD 125dB), with dynamic rage/SNR of 130dB over USB2.0 connected to a general Windows 11 MiniPC.

As a hi-fi DAC, I think that'll do. 😉

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In closing: DAC Perceptible Perfection achieved - and as humans, desiring more.

While I believe that DACs have reached a "perceptibly perfect" level of performance already a number of years ago, that of course does not mean companies would or should stop releasing new models.

Fidelity is but one factor. Appearance, luxuriousness, uniqueness are in themselves subjective features we can spend money on to acquire, regardless of how we as audiophile enthusiasts might want to be seen as justifying purchases based on "sound quality". Let's not be silly and claim that this is what it's really always about!

Furthermore, features such as the incorporation of DSP capabilities (like with the RME ADI-2 devices) would be other reasons for manufacturers to continue offering new devices for consumers.

Consider for example the fact that watches have already far exceeded the utilitarian need for telling time accurately in daily life. The level of precision that anyone needs has already been achieved since the days of the Seiko Quartz Astron 35SQ released on Christmas Day 1969.

Yet, while time precision has been achieved in wristwatches for generations, this has not stopped the release of new luxury (non-utilitarian) watches for collectors and the proliferation of "high-end" brands. Check out this report from the recent Watches And Wonders convention in Geneva. As technology improves beyond utilitarian needs (which any consumer can replace with devices of lower cost), beyond new features, inevitably, the Industry turns to satisfying the appetites of the high-end luxury buyer for new flagship products.

This dynamic however means that the fortunes of the Industry will track performance of other luxury goods. During times of economic contraction, the luxury industry will likewise feel the pain and we'll probably see the effect on the size of the industry, the number of exhibitors at audio shows, the health of the remaining brick & mortar high-end stores, etc. Notice for example the significant reduction in the China luxury market in that video above on Watches and Wonders. 

This is basically where we're at with DACs and likely other components such as amplifiers; any audio "high end" product. I don't know if we get final numbers available publicly, but it would be interesting tracking the physical size, new products, traffic, and number of brands exhibiting at shows like HIGH END Munich/Vienna over the years, and correlating that to other luxury markets to see relative demand for audio. Loss of revenue will also hit advertising and we probably will see changes in magazine vitality and the folks who cater to online hi-end content. Let's watch and learn how the ebbs and flows of macroeconomic factors affect audiophilia!

Hope you're all enjoying the music! Weather's getting better, so it's time for me to spend more time outdoors also...

Here's a nice track if you're looking for more female vocals to demo on your system - Nicole Scherzinger's "With One Look" from Sunset Blvd. (2024) - album DR13 stereo & multichannel/Atmos, good example of a stereo mix that has retained more natural dynamic range. I notice that this YouTube clip has deteriorated the sound quality unfortunately, so go find the actual recording:

PS: If you like music of the '80s, check out Kim Wilde's new album Closer (2025, multichannel/Atmos DR11). I've only heard the multichannel mix so far. Nice modern refresh of her pop/synthpop vibes!

Parting shot of the Topping DX9 from the listening position. 2-channel XLR out upmixed with Auro-Matic on the Integra receiver. Playing some Namewee's Ghosician (2021, DR6); pretty funny but can be crude and controversial Malaysian rapper.