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 | Cambridge Audio Edge A has more power - 100W against 70W into 8 ohms. That is about 1.5dB, which is a small step in loudness but real headroom on peaks. |
| Room size | depends | We rate Audio Research I/70 the better fit for a small room, and Cambridge Audio Edge A for a large room and a very large room. Match the amplifier to the room you actually have, not the one you want. |
| Built-in DAC | B | Cambridge Audio Edge A has a DAC on board; the other needs an external one, which is another box, another power lead and another purchase. |
| Analogue inputs | A | Audio Research I/70 takes more analogue sources - 4 against 3. |
| Use with a TV | depends | Only Cambridge Audio Edge A 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. |
| Room to grow | evenly matched | The same expansion options on both. |
| Amplifier type | depends | Audio Research I/70 is Tube and Cambridge Audio Edge A 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 | Audio Research I/70 takes up about 24% less shelf area (1428cm² against 1867cm²), and it is 65mm shallower, which is the measurement that decides whether a rack door shuts. |
| Price | B | Cambridge Audio Edge A costs less - $6,499 against $9,950 at list. |
| Watts per dollar | B | Cambridge Audio Edge A is the cheaper watt - about $65 per watt against $142. A blunt measure, and it says nothing about how either sounds, but it is the honest one for raw output. |
A Audio Research I/70 B Cambridge Audio Edge A
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?
Cambridge Audio Edge A is the easier recommendation: it leads on most of the measured areas and costs less. Take Audio Research I/70 if one of the "depends" rows above describes your system. If this sits under a television, Cambridge Audio Edge A is the one to buy - HDMI ARC means the TV remote controls the volume and there is no second box in the way. If you already own a DAC or a streamer, the built-in one is money you are paying twice for, and Audio Research I/70 becomes the more rational buy.
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.