Integrated Amplifiers

There's something comforting about a product with a singular focus, and Pass Labs' INT-25 fits that bill. A line-only integrated, it steers clear of the digital inputs, network functionality and onboard phono stage offered by many competitors. Instead, it presents itself simply as a conduit between your source(s) and speakers, combining a FET-based preamp and Class A power amp and nothing else. If that sounds somewhat 'basic', Pass Labs' history and the amplifier's £7200 price tag should suggest it's anything but. As does its mastery of music – but I'm getting ahead of myself…

The INT-25's stripped-down specification might put off prospective buyers seeking a one-stop-shop, but such an approach does have clear benefits. For the end user, it brings the freedom to pair the amp with a DAC, network player and phono stage of their choice, avoiding unnecessary duplication. And for designer Nelson Pass, it contributes even more to his simpler-is-better philosophy.

Baby Class A
California-based Pass Labs has been making amplifiers since 1991, beginning with the 75W monoblock Class A Aleph 0. Its range has since expanded to include stereo and mono Class A and Class AB designs, line and phono preamps, the HPA-1 headphone amplifier, and its INT integrated series. The INT-25 here is that range's entry-level amp, and is rated at 2x25W/8ohm. It's overshadowed by more powerful (Class AB) stablemates – the £8750 INT-60 claims 2x60W, and the £11,495 INT-250 [HFN Nov '17] a robust 2x250W.

All are only available in silver yet have slightly different stylings, and while the INT-25 misses out on the circular blue-lit meter of its brethren, it remains good-looking. It sits on four circular feet and is reasonably large at 431x152x440 (whd) and heavy (22.2kg) – although compared to the INT-250 it could be considered compact and lightweight. Meanwhile, two side-mounted heatsinks add a slightly industrial feel to an otherwise quite glamorous visage, where bevelled edges on the thick brushed aluminium front-plate frame its asymmetric layout. Controls are minimal – just a 63-step volume, a trio of input selectors, and mute and power buttons. A blue LED window gives a numerical indication of volume level, and smaller LEDs illuminate the chosen input.

With none of the du jour mod-con features, the amplifier's back panel is naturally uncluttered. Sat between two metal handles are just chunky loudspeaker binding posts for spade, banana plug or bare-wire connection, and a trio of line-level RCA inputs.

Simply Does It
This purity of design carries through to the INT-25's internal architecture. The preamp is a simplified single-ended version of the balanced JFET circuit used in the costlier INT-60 while the Class A FET power amp – a very elegant two-transistor configuration – is culled from Pass Labs' XA-25 model.

Incidentally, if that 2x25W seems rather parsimonious, especially for owners of insensitive speakers, then do not despair because that conservative spec. only denotes the amp's Class A reach, determined by its standing bias current. In practice, and ably assisted by a very substantial power supply, it'll deliver a lot more as the INT-25 ventures out into Class AB.