TOPPING D90 III Discrete DAC: Closer Examination

Whenever a brand uses numbers in its product naming scheme, it's usually a good assumption that the larger numbered-products are more expensive. With DACs and amps, this often translates to being physically larger too, as is the case here with the TOPPING D90 III Discrete. It's still plenty amenable for PC desktop though, measuring at 22 x 16 x 4.5 cm—actually smaller in all dimensions compared to the D70 Pro Sabre—and weighing 1.17 kg. The landscape profile used here means you can still mostly fit the stack under a VESA mounted monitor though, or at least alongside one. As with other TOPPING DACs, the D90 III Discrete uses thick CNC-machined aluminium alloy construction leading to a solid feel and increased stability on your desk, and comes in black or silver anodized finishes. These are then given a sandblasted matte finish that feels cold to the touch, and this silver version at least feels resistant to dust and fingerprints. I like the rounded edges, thus preventing any sharp corners, and the ridges on the side to prevent this from looking like yet another metal box. Given there are multiple D90 DACs from TOPPING, including three others with a very similar chassis, this discrete version differs by incorporating a window on the top that is theoretically allowing you to look at the PCB and the 1-bit DAC used here. The problem is it's a dark and thick panel, and there is of course no lighting inside, so you will struggle to see much unless you shine a light through and have your eye right next to the window.

There are the expected Hi-Res Audio and Hi-Res Audio Wireless badges on the top of the case—no MQA decoding here thankfully. The faceplate is quite thick and has the TOPPING logo on the top where it's curving upward slightly, reciprocated by another gentle curve on the bottom. This allows enough room in the middle for other items, including a power/selector multifunction button on the left, a monochrome OLED screen in the middle with the remote control receiver on the right bezel, and a smooth stepped wheel that defaults to volume control on the right. The wheel rotates without any stop points and there are no positional indicators for the wheel on the faceplate, so you need to rely on the display instead.


There isn't much to see on the sides given the lack of ventilation, with the aforementioned ridges making it also easy to hold the DAC as necessary. The QR code on the corner was unrecognizable by my phone, for what it's worth. The underside sports a certification sticker which also tells us the max power draw is ~27 W. There are four rubber feet at the corners which are screwed in place. These help lift the device and prevent scratches to the chassis while adding friction against the resting surface. The back side is where all connectivity options are found, including input and output options alike, although I wish the various sets were marked by a box to help those who might potentially be confused. Regardless, on the left we see the product name finally, in addition to the analog outputs in the form of balanced dual 3-pin XLR and single-ended RCA leading to a headphones amplifier or even a set of active speakers. The D90 III Discrete is generous on the inputs front, offering USB Type-B, coax, optical, Bluetooth 5.1, even AES and IIS for the prosumers here. Then we see a 12 V trigger that, when connected to a compatible device such as the A90 Discrete, can help daisy-chain the on/off signal to allow the combination to be powered on or off together. There is then the expected 3-prong power plug for the AC mains cable itself. I appreciate the tiny switch on the back too even if a larger one is better in helping locate it more easily when feeling around blindly from the front.


After all testing was done, I attempted to disassemble the D90 III Discrete, but it refused to do anything useful. When I felt like I was going to potentially damage something irreversibly, I decided to give up. There's really not a lot to see inside anyway, given the use of 1-bit DAC architecture. If you are unfamiliar with this, here's a helpful Wikipedia page so I don't have to spend a lot of time going beyond the scope of this review. In general, most DACs on the market are multi-bit, meaning they decode multiple bits simultaneously. 1-bit DACs, in addition to decoding a single bit at a time, also don't use a delta-sigma modulator to reduce audible noise as with typical delta-sigma DACs from the likes of ESS/AKM/Cirrus Logic/Burr Brown and others. This means they have to oversample at an extremely high rate, and it's generally harder to design a 1-bit DAC that performs as clean or "better" than a typical delta-sigma DAC. Note that a 1-bit DAC is not an R-2R DAC, despite the two perhaps looking similar in the PCB design. The D90 III Discrete uses 16 phases of TOPPING's new "PRSM" 1-bit DAC modules, with the upcoming D900 going for 32 such modules, so we know TOPPING is taking this seriously as a platform. The brand says it's also gone through several iterations and chosen specific components to get around some of the design challenges of a 1-bit DAC, including potential jitter with Altera's MAX II CPLD (complex programmable logic device) onboard, and everything down to the power supply is custom designed and manufactured around the new DAC. There is an undisclosed SoC on board to help process the digital signal, allowing for a 10-band PEQ to be applied too. Additionally, TOPPING is using the Qualcomm QCC5125 Bluetooth SoC for wireless connectivity. Given the native-DSD playback from the 1-bit DAC here, the D90 III Discrete is rated for up to 512 DSD and up to 32-bit, 768 kHz PCM playback with exceptional—for a 1-bit DAC—THD and dynamic range numbers marketed by the brand.