A valve amplifier against a solid-state one. They are not really rivals: they differ in character, in what they will drive and in what owning them involves, so start there rather than with the watts.
| Area | Better | Why |
|---|
| Power | B | PS Audio BHK Mono 300 has more power - 300W against 140W into 8 ohms. That is about 3.3dB, so it plays usefully louder before it runs out and has more in hand on peaks. |
| Room size | depends | We rate PS Audio Stellar S300 the better fit for desk or near-field listening, a small room and a mid-size room, and PS Audio BHK Mono 300 for a very large room. Match the amplifier to the room you actually have, not the one you want. |
| Grip on hard loads | evenly matched | Both behave much the same into 4 ohms - output nearly doubles (300W and 600W). |
| Noise floor | A | PS Audio Stellar S300 is the quieter design on paper - 100dB against 85dB. Audible mainly with sensitive speakers in a quiet room. |
| Analogue inputs | evenly matched | The same number of line-level inputs (1). |
| Amplifier type | depends | PS Audio Stellar S300 is Solid State and PS Audio BHK Mono 300 is Hybrid. Valve designs are usually warmer and softer at the limits and need their tubes replaced eventually; solid state is the lower-maintenance choice. This is a taste and ownership decision, not a quality one. |
| Shelf space | depends | PS Audio Stellar S300 takes up about 15% less shelf area (1316cm² against 1544cm²), and it is 51mm shallower, which is the measurement that decides whether a rack door shuts. |
| Price | A | PS Audio Stellar S300 costs less - $1,999 against $8,499 at list. |
| Watts per dollar | A | PS Audio Stellar S300 is the cheaper watt - about $14 per watt against $28. A blunt measure, and it says nothing about how either sounds, but it is the honest one for raw output. |
A PS Audio Stellar S300 B PS Audio BHK Mono 300
depends neither is better in the abstract - it turns on your room, your system or how you will use them. Only specs published for both amplifiers are judged; anything missing on either side is left out rather than guessed.
Which should you choose?
PS Audio Stellar S300 has the edge on paper, though not by much. The rows marked "depends" are more likely to decide this than the score is. Start with the room. In a large or open-plan room, or with speakers that are hard to drive - low sensitivity, or an impedance that dips - PS Audio BHK Mono 300 has the headroom, and headroom is what stops an amplifier hardening up on peaks. At desk distance or in a small room, 140 watts is already more than most people ever use, and the extra 160 watts would be headroom you pay for and never hear - we rate PS Audio BHK Mono 300 poorly for near-field use for exactly that reason. Think about the whole system: the roughly $6,500 saved by taking the cheaper one would buy better speakers or a subwoofer, which does more for the sound than the difference between two competent amplifiers.
What a spec sheet cannot show: how either sounds with your speakers, how the controls feel day to day, and what the app is like to live with - which is where most all-in-one amplifiers are actually won or lost. Power figures are the manufacturers' own and are not measured to a common standard, so treat small differences as noise. If you can hear both, that will tell you more than any row above.