Short answer
Both are desktop amplifiers, $600 against $599.
The Topping A90 Discrete reaches 100 dB on 567 of the 567 models here, the Soncoz SGA1 on 566.
| Specification | Soncoz SGA1 | Topping A90 Discrete |
|---|---|---|
| Power into 32Ω | 407 mW | 2.0 W |
| Power into 150Ω | 207 mW | 480 mW |
| Power into 300Ω | 210 mW | 250 mW |
| Power into 600Ω | 105 mW | 125 mW |
| Output impedance | 0.1 Ω | 0.1 Ω |
| Output noise | 1.8 µV | 0.2 µV |
| Price | $600 | $599 |
| Headphones it reaches 100 dB on out of 567 | 566 | 567 |
| Balanced | Soncoz SGA1 | Topping A90 Discrete |
|---|---|---|
| Socket | 4-Pin XLR + 4.4mm | XLR4 + 4.4mm |
| Power into 32Ω | 407 mW derived | 6.7 W |
| Power into 300Ω | 840 mW | 1.0 W |
| Output impedance | 0.05 Ω | 0.2 Ω |
| Output noise | 3.6 µV | 0.2 µV |
| Headphones it reaches 100 dB on out of 567 | 566 | 567 |
Through the balanced sockets the Topping A90 Discrete reaches 100 dB on 567 of the 567 models here and the Soncoz SGA1 on 566. Derived figures are worked out from the loads the maker did publish.
| Load | Soncoz SGA1 | Topping A90 Discrete |
|---|---|---|
| 32 Ω | Derived | Published |
| 150 Ω | Derived | Derived |
| 300 Ω | Published | Published |
| 600 Ω | Published | Derived |
Both makers publish a power rating. Soncoz SGA1 publishes at 300 Ω and at 600 Ω; Topping A90 Discrete at 32 Ω and at 300 Ω. The other rows are worked out from those.
So the two columns are not equally firm row by row: at 600 Ω only the Soncoz SGA1 figure is the maker’s own and at 32 Ω only the Topping A90 Discrete figure is the maker’s own. On those rows the derived number is the one to doubt first.
1 headphone reaches 100 dB on the Topping A90 Discrete but not on the Soncoz SGA1 — Symphonium Titan.
2 headphones stay below the audible-hiss threshold on the Topping A90 Discrete but cross it on the Soncoz SGA1 (Simgot EA500, Tanchjim EA FORCE).
566 of the 567 models here reach 100 dB on both.
Headroom is at a 100 dB SPL peak.
The widest gap on the list is the Shure SE846: Topping A90 Discrete has +47 dB of headroom there against +35 dB. 12 dB is about 16 times the power, which matters for peaks rather than for how loud the music sits.
Hiss below about 20 dB SPL is inaudible in a quiet room.
| Headphone | Impedance | Needs | Soncoz SGA1 headroom | Topping A90 Discrete headroom | Soncoz SGA1 hiss | Topping A90 Discrete hiss |
|---|---|---|---|---|---|---|
| Shure SE846 | 9 Ω | 0.04 mW | +35 dB | +47 dB | 20 dB | 0 dB |
| Campfire Audio Andromeda 2020 | 9 Ω | 4.0 mW | +15 dB | +27 dB | -0 dB | -20 dB |
| Audeze LCD-2 Classic | 70 Ω | 0.79 mW | +25 dB | +31 dB | -2 dB | -21 dB |
| Beyerdynamic DT 1990 Pro (250Ω) | 250 Ω | 0.63 mW | +25 dB | +27 dB | -7 dB | -26 dB |
| HiFiMAN HE400se | 25 Ω | 7.9 mW | +16 dB | +25 dB | -8 dB | -27 dB |
| Audio-Technica ATH-R70X | 470 Ω | 1.6 mW | +19 dB | +20 dB | -14 dB | -33 dB |
| Sennheiser HD 600 | 300 Ω | 6.6 mW | +15 dB | +16 dB | -18 dB | -37 dB |
| HiFiMAN Susvara | 60 Ω | 50 mW | +8 dB | +14 dB | -20 dB | -39 dB |
The Soncoz SGA1 costs $1 more than the Topping A90 Discrete, and on these three axes the money buys nothing: among the 567 models here there is not one that the Soncoz SGA1 handles and the Topping A90 Discrete does not — not on power, not on the one-eighth rule, not on hiss. The traffic runs the other way: the cheaper Topping A90 Discrete drives one model to 100 dB and keeps 2 below the audible-hiss threshold that the Soncoz SGA1 does not.
Only published figures count here; blank axes are counted separately.
Each in full: Soncoz SGA1 and Topping A90 Discrete.