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 | A | PS Audio BHK Signature 250 has more power - 250W against 40W into 8 ohms. That is about 8dB - a different class of amplifier rather than a bigger version of the same one, and far more than most rooms will ever ask for. |
| Room size | depends | We rate PS Audio BHK Signature 250 the better fit for a large room and a very large room, and Naim Uniti Atom for desk or near-field listening, a small room and a mid-size room. Match the amplifier to the room you actually have, not the one you want. |
| Built-in DAC | B | Naim Uniti Atom has a DAC on board; the other needs an external one, which is another box, another power lead and another purchase. |
| Analogue inputs | evenly matched | The same number of line-level inputs (1). |
| Use with a TV | depends | Only Naim Uniti Atom has HDMI ARC, so the television can drive it directly and one remote controls the volume. If the system is for music only, this changes nothing. |
| Headphones | depends | Only Naim Uniti Atom has a headphone output. Worth something if you listen late, nothing if you never do. |
| Amplifier type | depends | PS Audio BHK Signature 250 is Hybrid and Naim Uniti Atom is Solid State. 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 | Naim Uniti Atom takes up about 49% less shelf area (781cm² against 1544cm²), and it is 40mm shallower, which is the measurement that decides whether a rack door shuts. |
| Price | B | Naim Uniti Atom costs less - $3,799 against $4,249 at list. |
| Watts per dollar | A | PS Audio BHK Signature 250 is the cheaper watt - about $17 per watt against $95. A blunt measure, and it says nothing about how either sounds, but it is the honest one for raw output. |
A PS Audio BHK Signature 250 B Naim Uniti Atom
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?
The usual trade-off: PS Audio BHK Signature 250 measures better, Naim Uniti Atom costs about 11% less. With most speakers in most rooms that gap is smaller in practice than it looks here. 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 Signature 250 has the headroom, and headroom is what stops an amplifier hardening up on peaks. At desk distance or in a small room, 40 watts is already more than most people ever use, and the extra 210 watts would be headroom you pay for and never hear - we rate PS Audio BHK Signature 250 poorly for near-field use for exactly that reason. If this sits under a television, Naim Uniti Atom is the one to buy - HDMI ARC means the TV remote controls the volume and there is no second box in the way.
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.