TOPPING A90 Discrete Amp: Closer Examination

The TOPPING A90 Discrete released before the D90 III Discrete did, however it was clearly intended to be stacked with TOPPING's previous D90-series DACs including the D90 III Sabre, D90 SE, and D90 LE—talk about brand confusion! With the newer D90 III Discrete following a similar design language as the other three DACs, it's no surprise then that the A90 Discrete matches it very well too. We get a similar CNC-machined aluminium alloy chassis at 22 x 16 x 4.5 cm and slightly higher mass at 1.25 kg, and the A90 Discrete also comes in black or silver colors to match the DAC. There's the expected Hi-Res Audio badge on the top near the faceplate, which in turn has the brand and product name on the front by the left side. The geometric pattern by the corner houses the remote control receiver, with the output selector and power indicator lights above. The input channel selector indicator lights are next to these, and they all come marked with appropriate legends for easier identification. Then we see large dot matrix-style LED volume indicators, followed by the headphone outputs in the middle in the form of full-size 4-pin balanced XLR, 4.4 mm balanced, and 6.35 mm (1/4") single-ended connections. A similar volume knob/multi-functional button as before on the right side wraps things up on the front.


This is a solid state amplifier and won't get hot as some tube amplifiers will, so once again we see no ventilation on the side or top. Things get busy on the back, enough to were TOPPING has actually marked the inputs and outputs similar to how I would have preferred the D90 III Discrete also do. On the left is an accessory port allowing the A90 Discrete to be connected to TOPPING's Ext90 input extender, which adds three XLR stereo inputs and an RCA stereo input in addition to the one of each input type you already get here. This means that you could have a plethora of different inputs feeding the A90 Discrete amplifier, although realistically most people will be content with the one set each available here, since you can use both simultaneously anyway. You can also use the A90 Discrete as a preamp, and thus we get dual 3-pin XLR and a set of RCA outputs too. We see the same 12 V trigger as on the D90 III Discrete DAC and there is also a Type-C port above the accessory port for any firmware updates for the amplifier itself, which is nice to see for those looking for a longer-term solution. A handy toggle helps eliminate any ground loop noise—set it to GND in normal use and Lift if you experience said noise. Rounding off the back panel is another of the same 3-prong power cable inputs and the associated on/off switch itself.


The sticker on the bottom confirms the amplifier is rated for much more power in compared to the DAC, which makes sense. Surprisingly, we see four smaller hemispherical rubber feet on the corners here as opposed to the more substantial ones on the DAC, although this tells me TOPPING intends for the user to stack the amp on top of the DAC. Once again disassembly was proving less than trivial, perhaps there is something with this chassis design I am missing. Here too there isn't much to see if you don't understand what the discrete components employed for amplification are doing. The 90 Discrete uses four TOPPING NFCA (nested feedback composite amplifier) modules, each containing 39 transistors, in a fully-balanced voltage-current hybrid feedback architecture, providing as much as 49 Vpp output voltage off the balanced connectors and 25 Vpp off the single-ended output in addition to a high output current of 1.1 A continuous/5 A peak, all under 0.1 Ω output impedance. The amp also uses relays and resistor networks to allow R-2R stepped volume control for increased precision and further reduced channel imbalance from the already impressive user experience in previous TOPPING amps. Given the A90 Discrete has been out already, we've already seen it independently tested to confirm the unit has ultra-low distortion and high dynamic range/SINAD despite the discrete architecture.