Setup and Performance

Setup

If you decide to have the TOPPING D90 III Discrete DAC paired with the A90 Discrete amplifier as a stack, you have the option of going with balanced dual 3-pin XLR interconnects or single-ended dual RCA interconnects. If you only care about the power output of the A90 Discrete, you can feed it either a single-ended or balanced connection from the DAC. The latter only really helps further reduce channel crosstalk and input sensitivity, but we see the A90 Discrete is rated to have an even cleaner sound off the single-ended inputs. Not that those incremental changes well beyond human hearing really matter though, so go with what you have on hand. Seen above are the two connected via XLR interconnects I had readily available—as simple as that. I also generally prefer having the amplifier above the DAC, so the headphone outputs are closer to reach. That said, I did not notice any thermal issue going the other way round, and this also allows you to see the window in the DAC in case that interests you. The only issue is the DAC clearly has larger feet, so you may want to go the traditional route after all. Some also use a dedicated rack mount for each component, which also helps manage the myriad of cables on the back. At the very minimum, there will be the two power cables and the interconnects. You could go with Bluetooth input to the DAC, but no one purchasing an expensive DAC is doing that unless temporarily for convenience with mobile devices. I also had the USB cable attached to the D90 III Discrete thus, especially since I was testing this as a desktop stack with my PC. The ensemble is pretty solid and won't move despite all the cables hanging off the back, in case you have it near the edge of your desk.


The shared design language as well as the common dimensions of the chassis on both units make for a well-matched stack. Turn both on using the switches on the back and you will hear a soft click before the DAC display turns on to show the TOPPING logo briefly before giving way to real time information on the input and output type, the sampling rate, the volume, and PCM/DSD format indication. The DAC, and the amp too, default to -30 dB (on a scale of 0 to -99 dB). The display on the DAC of course makes it easier to see in 0.5 dB increments by default, whereas the dot matrix-style LEDs on the amp allow for a 1 dB step—still easily visible, as evident from the two values chosen above. The indicator lights on the left of the amp are also handy, although I must say having a matching display on the A90 Discrete would have been more useful—I've clearly become too used to the D70 Pro Sabre/A70 Pro stack with the two color displays.


The absence of a display on the A90 Discrete amplifier also makes it less user-friendly to do a lot of things, be it changing the gain level or accessing the setup menu. The former relies on you pressing down the volume knob and turning it clockwise (high gain) or counterclockwise (low gain) by two discrete steps within 1.5 seconds. Press and hold it without turning, and now it's a power button itself. The setup menu relies on the LEDs, allowing you to change their brightness, having the volume control on/off, trigger mode on/off, and assigning volume memory settings. The DAC, on the other hand, has more extensive menu and here the display helps out even if you need to use the power switch on the back to access the menu—not very elegant. There are 18 options, which can take a while to access on that thin display showing two items per screen, and I'll highlight the more interesting stuff such as DSD bypass in DAC mode, IIS phase/DSD channel/DSD flag settings, and of course the new PEQ feature that TOPPING has incorporated here—more on this shortly. The user manuals do a decent job walking you through all the options and how to use them, although I expect TOPPING has heard the complaints about the display given the upcoming D900/A900 flagship stack appears to have large displays on both units again.


I did try Bluetooth input on the D90 III Discrete DAC to see how well it worked, with the DAC automatically going to pairing mode and recognized by my phone. It offers Bluetooth 5.1 connectivity with a rich codec support including SBC, AAC, aptX, aptX HD, aptX Adaptive, and LDAC, with my phone in LDAC mode doing a good job offering that flexibility of having the stack on my office desk when I cared less about the best possible sound quality and more about convenience.


The bulk majority of my testing was done with USB input to the DAC and here the display will confirm that the D90 III Discrete defaults to 32-bit, 48 kHz PCM playback in Windows. Indeed, the sound controls in Windows confirm as much and you can get 24 or 32-bit PCM playback up to 384 kHz directly without needing any drivers. Your preferred media player should also see it and allow PCM/DSD playback, with the latter going to DSD 512 natively. Roon also sees the device but doesn't identify it, so you have to enable it and set it up in the audio settings tab there.


If you have a device that doesn't accept UAC 2.0, you can toggle the DAC to be in UAC 1.0 mode. Sometimes this doesn't help either, especially with specific devices on older operating systems. In such cases, or if you simply want to try other options, then the TOPPING-skinned XMOS/Thesycon USB audio device drivers will be of interest to you. You can find the installer on the downloads page, although note it doesn't explicitly talk about the D90 III Discrete—more on this shortly again. The latest version at the time of testing was v5.62.0 from a couple of months ago. Installation is trivial as seen above, and these drivers now allow you to make the most of the TOPPING stack within the Windows operating system.



What these drivers do after installation is create a new output device in Windows, also providing access to the TOPPING USB DAC Driver Control Panel. You would mostly use these drivers in newer Windows builds if you want to have the stack as an ASIO (Audio Stream Input/Output) device. Set the format to your choosing and choose the buffer size based on latency requirements. With that done, go to your media player of choice. I demonstrated above with JRiver and Roon again and set the audio player to the same output. At this point, you can implement further tweaks, but those are player dependent. These drivers also provide 16-bit playback support as seen above, and Roon automatically allows for native DSD playback up to DSD512. Given the 1-bit architecture here, I was primarily using Roon with the D90 III Discrete to play my tracks in native DSD mode, albeit of course I tried PCM upsampling too.


I mentioned before how TOPPING has added PEQ support to the D90 III Discrete, and this comes in the form of a new piece of software called TOPPING Tune, which can be downloaded here. The installer for the current version v1.02 is ~26 MB in size and the final installation takes ~88 MB of storage. The installation process itself is self-explanatory, although I noticed the program takes up 6-8% CPU usage at times which is not great. Add to this random RAM usage spikes too and there's clearly work to be done to optimize the program.


TOPPING Tune is quite well featured, allowing you to import your own target and frequency response curves as I did with the Harman Over-Ear target and my measurements of the MOONDROP COSMO headphones. You then get 10-band PEQ, including with five filter types, and a preamp with a visualizer for everything as seen in the video. Do be warned that the drop-down menus are overly sensitive though, I was originally frustrated by how careful I had to be with my mouse around the filter type selection since it can inadvertently change as demonstrated in the video. Use the keyboard for the menus and typing the frequency, dB, and Q-factor values instead of relying on the wheels, and now it's a lot more stable. Once you are happy, you can save it locally and/or upload to the D90 III Discrete, with the DAC able to store up to five PEQ profiles on board. These are then available for use via the device menu, allowing you to have PEQ over all digital inputs except IIS which is directly connected to the DAC module and thus cannot process the EQ signal beforehand. This can be very handy thus, and I am encouraged to see this becoming a feature for desktop use too, not just mobile sources.

Audio Performance

The TOPPING A90 Discrete is really all I can ask for when it comes to a neutral, clean, powerful amplifier. It's not rated for crazy amounts of output power as with the TOPPING A70 Pro, which actually made it harder to use with more sensitive headphones and IEMs. In fact, I mentioned how the A70 Pro felt like it was just there to brag about a metric most people will never use. The A90 Discrete still provides more than enough power off the balanced outputs—9.8 W per channel at 16 Ω, 6.7 W at 32 Ω, 4 W at 64Ω, 1 W at 300 Ω, and 500 mW at 600 Ω. Go with the single-ended output and you get up to 3.3 W per channel at 16 Ω going down to 250 mW at 300 Ω. I also appreciate the gain settings doing different things depending on the outputs, with a minor effect from the inputs too. This allows for the A90 Discrete to be actually usable with most IEMs on the market too, especially with the precise volume control and no channel imbalance at lower volumes. The issue is that less expensive headphone amplifiers, including from TOPPING, are probably enough for most people reading this review. The A90 Discrete finds itself in a hard spot this way, especially since I don't see any particular impact on the sound signature here either compared to other clean, neutral amplifiers down to the dark background expected for a halfway decent amplifier in 2024.

It's actually the DAC which is far more interesting, with 1-bit DACs usually measuring worse than delta-sigma multi-bit DACs. Such is TOPPING's history that people would probably crucify the brand's engineers if they put out something that didn't meet their expectations, and somehow this manages to be super clean sounding while still being engaging. It's not a warmer presentation as some R-2R DACs can sound, more like there's a tiny bit of extra presence in the mids which helps bring vocals more forward to my ears. We are talking tiny, tiny changes that may also be highly dependent on the headphones used though, but I found the D90 III Discrete to be generally a good pairing with neutral-bright headphones, such as the HIFIMAN planar magnetic lineup, with the upper mids now more filled out to my ears. On the flip side, mid-bass dynamics felt slightly softer compared to the TOPPING E70 Velvet, so right now I'm hoping the upcoming TOPPING R-2R DAC will be more to my liking and really take on more expensive sources. Obviously there's no change to the actual frequency response, with the DAC and amp combo measuring flat as expected. The D90 III Discrete has its strengths and weaknesses, but does make up with an increased feature set which now includes PEQ customization.