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.

Part II: Topping DX9 "15th Anniversary" Limited Edition DAC & Headphone Amplifier - PCM Filters, Frequency Response & DAC Resolution. (And Trump's ongoing oblivious narcissistic tariff buffoonery.) [Firmware 1.23 Update]

Continuing with the discussion in Part I, let's proceed with Part II of our look at the Topping DX9 "15th Anniversary" DAC as we wade into some of the technical capabilities and performance of this device.

As I discussed the other week, my belief is that for relatively "simple" devices like DACs where what we want is as-accurate-as-possible conversion of the audio data into the analog voltages, measurements are really all we need to characterize the accuracy, the transparency of the device using modern tests and instruments that are capable of capturing details beyond the ability of human hearing. The capability for any device to achieve transparency of course does not guarantee that we'll be able to enjoy the sound or the music which are determined by individual subjective psychological factors.

With that, let's jump into some PCM measurements of this Topping flagship product.

Part I: Topping DX9 "15th Anniversary" Limited Edition DAC & Headphone Amplifier - build, features, listening impressions & subjective luxury.

As many audiophiles will remember, the well-known DAC chip maker Asahi Kasei Microdevices (AKM) suffered a massive fire at their factory back on October 20, 2020 in Miyazaki Prefecture, Japan. This resulted in a shortage of their chips for awhile until they rebuilt the plant and started offering devices again by the end of 2021.

In June 2021, AKM issued a "last time buy" notification for final stock of a number of their products. This included their top-of-the-line DAC chip, the AKM AK4499EQ which was initially released in January 2019 and had made its way into a number of devices over the ensuing couple of years. By later 2021, some devices like the HiFi Rose RS150 had to transition to ESS. With 4 channels, a published THD+N of -124dB (mono mode), 137dB SNR in stereo (140dB mono), DSD "direct" (volume bypass), this chip remains a formidable converter even in 2025 with newer generations of AKM and ESS chip DACs. While audiophiles and manufacturers like to talk about discreet DACs like R2R stuff or custom "Ring" DACs, or DSD-processing DACs (like Meitner products or Playback Designs), while I'm sure they sound great, there is no evidence that these are capable of achieving better objective resolution than state-of-the-art converter chips from semiconductor companies with significant R&D resources.

For comparison, based on company specs, the current premium DAC chips are ESS's ES9039PRO rated at -122dB THD+N mono, and 140dB SNR mono. And AKM's current flagship, the 2-channel AK4499EX DAC released in 2021 listed as THD+N -124dB and SNR 135dB stereo (138dB mono). The AK4499EQ as a 4-channel DAC is a much more complicated chip than 2 AK4499EX's because it also incorporates the sigma-delta modulator internally while the AK4499EX needs to be fed 7-bit modulator data at 5.64/11.29MHz from a separate source like the AK4191EQ ΔΣ Modulator!

So, basically, as a single chip, the discontinued AK4499EQ after only about 1.5 years in production, remains the highest performing device among its peers after all these years; on paper at least.

And that's why I bought one of these for my system - the Topping DX9 "15th Anniversary" Limited Edition DAC & headphone amplifier (US$1299, CAD$1900, depending on tariffs you might do better ordering from China through AliExpress):

This is Topping's flagship DAC, released in late 2023. It's said to be limited edition due to the restricted number of DAC chips; I connected with Topping and was told in total they made about 1800 units.

I bought this unit from the usual retail channels and have no affiliation with the company.

Part II: Topping PA5 Mk II Plus (PA5II+) Class D amplifier review. Power, Distortion, the Subjective and on Hi-Res amplification.

I mentioned previously that this is a very unobtrusive amp. With the shipped plastic protector off, notice the low contrast of the lettering with the black front makes it even less obtrusive! This was why I left the plastic protector on to take the photos last time to better show the labels for the switches.

I introduced the Topping PA5 Mk II Plus last time in Part I with some initial measurements. This time let's keep going as we explore the power capabilities of this little audio amplifier, examine playback fidelity, and discuss a bit of the subjective performance.

Unless otherwise specified, these measurements were done with the amplifier connected to standard 4Ω and 8Ω power resistors as load, both channels driven, 20Hz-20kHz bandwidth for distortion measurements, unweighted. The Linear Audio AutoRanger allowed automatic gain/attenuation to keep the signal from getting too "hot". Signal from the AutoRanger is fed to the prototype Cosmos Scaler as a preamp for the E1DA Cosmos ADC operating in mono mode. High resolution signal generator DAC is the SMSL DO100 connected to Intona USB isolator. No special cabling, the 3' female XLR-to-TRS balanced cable was just something decent and generic like this, likewise generic RCA was totally fine. Seriously audiophiles, that's all we need for hi-fi sound quality.

Let's get to it!

Part I: Topping PA5 Mk II Plus (PA5II+) Class D amplifier review. (And RME ADI-2 Remote, "cultural pressure" for subjectivist audiophile reviews to include measurements?)

Over the last few months, I've been exploring the performance of the TI TPA3255 Class D chip amps including the AIYIMA A08 Pro, Fosi Audio TB10D, and AOSHIDA A7. Overall, we've seen very good results from these little amplifiers and I think they represent a level of low-distortion performance at a price point that is very attractive to many hi-fi hobbyists.

Depending on the power supply mated to the amplifier, measurements have been showing low output impedance up to 10kHz typically (<0.2Ω up to 10kHz), something like 80+W into 4Ω with less than 0.1% THD+N, and a -80dB Triple-Tone TD+N result at 1W into 4Ω which is excellent considering the prices of these little amps typically at less than US$150 depending on the features you want like Bluetooth input, VU meter, etc.!

Given the track record of these TI devices so far, this time, let's look at another chip amp which is based on an undisclosed part, not the TPA3255, although I can confirm it is a TI TPA chip. In my discussions with John Yang at Topping, the intent is to allow audiophiles to judge the product based on sound quality merits rather than focus too much on exactly which Class D part was used since the design around the chip is very important. Fair enough, and that's exactly what we aim to do here anyways since even with the previous TPA3255 amps reviewed, there were objective differences to find even if subjectively, differences might not be as noticeable.

I bought this Topping PA5 Mk II Plus (which I'll abbreviate as PA5II+ for simplicity) myself from Amazon, currently around US$325 with the intent to use in my own system. Since I'm interested in "high-fidelity" (not merely "euphonia"), I was interested to see how well this would compete with the DIY Hypex nCore NC252MP we measured a few years back. I like the feature set that it offers. On paper, it should provide the power I need and if the hi-fidelity performance is excellent, it could certainly be a listening "reference" here even though to be honest, I still love the Hypex's capabilities and would have no issue with enjoying the music from the inexpensive TPA3255 devices either.

MEASUREMENTS: Topping HS02 USB 2.0 isolator. (This works with the E1DA Cosmos ADC; and the Topping + Intona "double isolation" of DAC and ADC.)

Hey guys and gals, I must be a sucker for relatively inexpensive USB galvanic isolators. To be honest, this is mostly because I look for ways to lower noise on my measurement testbench, not that I'm concerned with the actual audiophile sound system these days! ;-)

Today, let's have a look at the recently released Topping HS02 USB2.0 isolator (currently ~US$100). This is an update to the previously reviewed HS01 last year. As you can see from the picture and specs, the box now has selectable USB-A/B connectors or USB-C. Isolation is not just applied to the in/out USB data connectors, but also the auxiliary power input with filtering which means the device could stay free of noise even if we plug in a power source with some noise in it. As usual, be mindful of power-hungry USB-powered devices which will require auxiliary power input.

Furthermore, Topping has improved compatibility now with the ability to negotiate USB2.0 low (1.5Mbps)/full (12Mbps)/high speeds (480Mbps). I can confirm that my low speed wireless keyboard dongle works fine.

The diagram showing the path of the data and power connections is relatively clear printed on top. Inside the box are a couple of pamphlets - the black one is the warranty card and Topping catalogue, and the white user manual. There's a short USB-A to USB-B cable in the plastic bag.

Hi-Res THD(+N) vs. Output Level Measurements (ESS "HyperStream" vs. AKM vs. TI/Burr-Brown). And a bonus R-2R!

Notice last time as I ended off the post, I showed what I think is an interesting "high resolution" graph of THD(+N) vs. Output Level for the Topping D10 Balanced which uses the ESS ES9038Q2M chip. This was spurred on after some discussions on glitches and anomalies one might see due to the "HyperStream" architecture of the ESS chip.

These days, other than the occasional fully multibit or discrete R-2R DACs, the vast majority of what we're using are multibit/multilevel sigma-delta devices. This includes the brands I have listed in the upper graphic; Asahi Kasei Microdevices (AKM), ESS Technology, and Burr-Brown (which was acquired by Texas Instruments in 2000). We'll also talk about the Philips later. ;-)

Today, let's have a look at "high res" THD(+N) vs. Output graphs (XLR output where possible to keep noise as low as possible) comparing different DACs from these companies...

MEASUREMENTS: Topping HS01 - USB 2.0 Isolator & Ground Loop Eliminator (and a listen to Santana's "Blessings and Miracles")

Hey everyone, as you might be aware, I'm not a fan of USB "doohickeys" in general use. You know, all those USB boxes that are supposed to clean up your signal, or maybe reduce jitter, or "regenerate" this and that. Especially if you're not sure if you actually need it; some of these devices cost hundreds of dollars. On the lower price end, I had a look at the AudioQuest JitterBug FMJ last year which was a rather disappointing product.

Having said this, there are devices that can provide benefits like USB isolation for things like DACs. For example, the USB1 inexpensive ADuM4160 devices like this Nobsound ADuM4160. The problem is that this is only operating up to USB1 12Mbps "full speed". Furthermore, one would be limited to 24/96 performance even if the device is able to fall back and negotiate as USB Audio Class 1.

Enter the Topping HS01 (~US$70), a little black metal USB2.0 box advertised as providing galvanic isolation (to 1kVrms), for data and power lines with USB-B (to computer), and USB-A (to audio device) ends. Furthermore, there's a USB-C plug for devices that need extra power.

[Note: This device is not compatible with USB1.0/1.1. So don't be plugging in keyboards and mice to this. Non-audio devices like USB2 memory sticks and even my smart phone were fine. I have not tried plugging a USB2 hub up to this point so there might be issues there.]

REVIEW: Topping D90SE DAC - Part III: Subjective Impressions, AMPT, and Summary. A few words about "warmth" and "accuracy" in sound systems.

This is the final part of my trilogy review/evaluation of the Topping D90SE DAC (see Part I, and Part II for the objective testing results).

As we end off, let's close with a discussion of subjective impressions developed over many evenings of listening (about a month or so). I've described the soundroom previously in some detail and for the two channel system, the main amplifier is my home-assembled Hypex nCore NC252MP, main front speakers are the Paradigm Reference Signature S8 v3, and dual subs (main Paradigm SUB1 with the little Polk PSW111). The Topping D90SE feeds my Emotiva XSP-1 preamp. All cabling is balanced XLR from DAC to amplifier (no need to fret, inexpensive Monoprice Stage Right XLR runs are all ya need, feel free to spend more on cables if you see fit of course).

I listened both with and without DSP room correction activated; generally I prefer with DSP. Knowing the frequency response characteristics (flat to 20kHz) and setting to "Fast Roll-off Linear" (Filter 5) allows me to use the same DSP settings for my room interchangeably with the RME ADI-2 Pro FS Black Edition without need to remeasure (equivalent frequency and time-domain performance). As discussed before, one of the benefits of a high quality DAC is that we can have even more headrooom with DSP processing whether it be full room correction or applying volume normalization like ReplayGain.

MEASUREMENTS / REVIEW: Topping D90SE DAC - Part II: Resolution

In this Part II of the review of the Topping D90SE DAC, let's focus on the performance that this DAC can achieve. As you can see in the picture above, I've got the machine on the test bench ready to capture some data. Given the anticipated performance as described in Part I last time, the E1DA Cosmos ADC is used for the measurements being presented today.

As you can see on the LCD screen, it's playing DSD512 (22.6MHz) material at the time of this picture. For a more complete examination of the device's performance, let's see if we can capture both PCM and DSD performance.

This device does have a broad number of features, so let's try to hit the key (and also some not-so-key) features to better understand how well it works and if there are nuances that the audiophile should be aware of. As readers here I'm sure are aware of over the years, objective testing can often show anomalies that listening tests easily miss due to the limitations of human hearing and cognitive ability. Sure, one could argue that inaudible limitations are not important. I'd like to think that in principle, audiophiles have an interest in achieving both technical perfection as well as immaculate subjective performance. 

MEASUREMENTS: Topping DX3 PRO V2 (LDAC version) - plus frequency/amplitude stepped sine measurements, a quick look at the 8kHz USB PHY packet noise, and AirPods Pro "Spatial Audio" coming...

So I got another DAC here at home - purchased through usual retail channels of course :-).

The Topping DX3 PRO (~US$220) is a device meant for those who want wired (S/PDIF TosLink, Coaxial, USB) as well as flexible Bluetooth 5.0 wireless input. There are 2 versions of the DX3 PRO out there - the earlier version reviewed/measured at Audio Science Review by Amir and the newer one which I have here with LDAC support (Sony-developed "high resolution" Bluetooth CODEC, also measured by WolfX-700) released in late 2019.

At some point, I figure it would be interesting to compare how the various Bluetooth codecs perform since this device can accept the lowest common denominator SBC, plus AAC, aptX, aptX-LL (Low Latency), aptX-HD, and LDAC audio - about as broad a range as I've seen among Bluetooth DACs (here's a good primer on these acronyms).

For today, let's examine the device's standard DAC performance and run it through my typical procedure with a few new measurement variants to see how it performs.

MEASUREMENTS & LISTENING: Topping D30 DAC by Greg Dunn. (And briefly, more USB cable nonsense.)

[Ed: Every once awhile, it's a pleasure to have guest posters adding their voice to this blog! There are many folks out there doing measurements, experiments, and I've certainly been in contact with a number of audiophiles with great stories about the gear they have, music they love, and the audiophile pursuit in general!

A few weeks back, Greg got in touch with me around the Topping D30 DAC that he has. This DAC was brought up in comment discussions back in 2018. The D30 measured quite well on Audio Science Review, but has been blasted as subjectively sounding bad - "like ass" as it were - on the Super Best Audio Friends forum. Elsewhere in that SBAF comment thread, the D30 was described as having "poor soundstage and poor timbre".

With this polarization of opinion, it's great to see Greg stepping up with his own opinion based on objective testing and subjective listening... Take it away, Greg!]

MEASUREMENTS: Topping D10 DAC. (And a few words on "absolute polarity / phase".)

Hey guys, getting busy around here as I'm preparing for summer holidays coming up in a couple of weeks :-).

I did want to post a "quick" report however on the Topping D10 DAC (<US$90) I got last week... It's for an upcoming project of sorts which I'll post on over the months ahead. What I wanted was a DAC that could be powered off USB, reliable with Window and Linux compatibility, that's reasonably portable, and of course of high signal accuracy.

Notice the DAC manual shows some AP measurement graphs... I guess Topping believes in showing objective accuracy :-). Nice.