Integrated Amp Reviews

"Oh Baby, pass the butter"—Brak (Space Ghost)
In the last year, a bunch of amps have come through my house—integrated and power, solid-state and tubed—and I've learned a lot from listening to each of them. The main lesson has been that anyone who thinks all amps sound the same is inexperienced, unobservant, philosophically brainwashed, deaf, or crazy. During the Pass Labs INT-150's ($7150) stay at my house, it cohabitated with three other amps: the Rogue M180 tube monoblocks ($5495/pair), the Simaudio Moon i3.3 ($3300–$4000, depending on options), and Pass Labs' own XA30.5 ($5500), which I kept on long-term loan, knowing I'd soon be reviewing the INT-150. I was able to listen to each of these amps side by side with each of the others.

The INT-150 had an overall drive and wide dynamics similar to those of the Simaudio Moon i3.3, the Pass amp getting the nod for its even greater sense of ease when playing loud. The INT-150 had a more forward top end than the sweet-trebled Moon i3.3, but overall, the Pass had a more natural soundstage perspective and a more even tonal balance. Both presented soundstages with the same sense of depth, but the INT-150 seemed to pass along to me more musical information than did the Simaudio, with better senses of reverberation decay and separation between instruments.

Next up were the Rogue M180s, which have become my reference for moderately priced tube amps. Running KT90 tubes, the Rogues gave me the midrange magic and stereo imaging that the solid-state Pass couldn't quite offer. Both could play loud with similar bass articulation, the Rogues sounding slightly fuller from midbass through midrange. Some people will like the INT-150's clarity and cleanness in the bass and midband; some will prefer the warmth and body of tubes. The INT-150's top end erred slightly on the forward side of neutral, with nice extension, while the Rogues sounded perhaps a little closed-in and forgiving in the top two octaves. It was in soundstage width and depth that the Rogues truly outshone the INT-150, presenting a more involvingly three-dimensional space in which the music could take place. Compared to the Rogues, however, the INT-150 gets the nod for better build quality.

The most interesting comparison was between the class-A/B INT-150 and its brother, Pass Labs' class-A XA30.5 power amp. In a way, I was reviewing four products for the price of two. As Nelson Pass told me, the INT-150 is an X150.5 strapped to some input relays and a volume control, and the INT-30A is the integrated version of the XA30.5. I often see questions on Internet forums asking for guidance in buying a Pass amp: a lower-powered class-A model, or a higher-powered class-A/B design? I hoped to shed some light on the sonic differences and similarities between these amps and integrateds.

The XA30.5 offered a much more relaxed, rounded, and even tonal balance than did the slightly forward and drier INT-150. The XA30.5 gave greater body to voices and instruments, with a purity and texture in the midrange that the INT-150 couldn't quite deliver. As I wrote in one of my more poetic listening notes, "the XA30.5 gives me more of the ether around the music. The actual air around the voices and instruments is more tactile—it has humidity and dust in it, the way it does in real life." On the other hand, the INT-150 had superb control in the bass, and never gave up while reproducing big dynamic swings. The XA30.5 occasionally crapped out in loud passages, and its less defined control of my woofers both made some music lose its rhythmic drive, and gave it a small case of bass bloat. Also, the INT-150 had a markedly wider soundstage than the XA30.5. I didn't expect that last difference, but I heard it with every recording I tried.

I liked both amps equally, but in different ways. When I listened to the XA30.5, I occasionally missed the INT-150; when I listened to the INT-150, I sometimes missed the XA30.5. But if I had to choose, I think I'd rather live with the XA30.5's shortcomings. If you're trying to decide between the XA30.5 and the X150.5, or between the INT-30A and the INT-150, you'd best listen to both of each pair. Your choice will come down to which speakers you're using, how loud you like your playback levels, your favorite music, and what aspects of performance are most important to you.

Unapologetically awesome solid-state performance
Pass Labs' INT-150 is an extremely well-built, gorgeously designed, good-performing integrated amplifier. It excels at offering wide dynamic range, great control, steady drive, and a broad soundstage. Though its midrange and top end are slightly forward, this is less a flaw than an aspect of its character. Its bass is tight and tuneful. While it lacks the midrange magic of fine tubed gear, the INT-150 does offer unapologetically awesome solid-state performance. The INT-150 is a true high-end product that is easy and fun to use.