One amp “killing” another? Nelson Pass vs. Bob Carver vs. Rotel

For years I’d used a Carver M500t. Definitely not an ideal amplifier, but it served its purpose, and was reasonably musical. Late last summer, I’d introduced a Rotel RB-1070 into the system. It was one of those issues where it sounded OK, but…well, more on that shortly.

After several months of searching and researching, I narrowed down my amplifier choices to a select few, and narrowed in on a couple that were available for an affordable sum, but were “sleepers” in terms of popularity or partly due to age, yet had sonics that were the equal of others more costly.

Nakamichi PA-7.

What I came into was a Nakamichi PA-7. I am not a big fan of Nakamichi (after some really bad experiences with an OMS-7 CD player, and the ensuing runaround), but I came across this via a note on the ToneAUDIO web site. The original PA-7 (not its later revisions) is a Nelson Pass “Stasis” design–the design was used by Nakamichi under license from Threshold, the high-end amplifier manufacturer. The design is very stable into all impedances, and uses no overall negative feedback. It also has a lot of energy storage–over 130,000 µF of capacitance in the power supply. Pass himself recommends this PA-7.

Keep in mind that Pass also designed the original Adcom GFA-555, another sleeper of an amp.

The Nak amp, though, is a formidable unit. Heavier enough to be a boat anchor, it has machined aluminum handles and heat sinks. The familiar “STASIS” logo adorns the front. The rear is unassuming as well–a pair of RCA inputs, left and right sets of binding posts, and a receptacle for the power cord. Four tall feet allow you to rest the amp on its back.

Despite my modest speakers (my Martin Logan project is still on hold), I immediately heard a difference.

The M500t, as a refresher, was an amplifier whose “transfer function” was modified to sound like an expensive high-end amplifier. (It was one of two models which won two high end magazines’ “amplifier challenge shootouts”, where Bob Carver successfully modified the amplifiers to sound exactly like a specific model of high-end amplifier.) I will admit that the amp did have sort of a musical, flowing quality to it, but it was plagued by a few minor issues, like noise, and possibly not delivering its full power. Age was working against it–the amp is in need of a new set of capacitors, and a full adjustment.

Vintage Threshold Stasis power amplifier.

The PA-7 comes across as a very dynamic and musical amp. Right out of gate, I heard an openness to the tonal quality, and excellent soundstaging. After it had warmed up (and it does get warm!), playing a few specific tracks stressed the amp’s dynamic abilities, effortlessly processing those spikes in the signal without missing a beat (literally). What really stood out was that flowing, musical quality that was inviting to listen to. The inner details really become evident as well, little nuances and textures I hadn’t heard before. The PA-7 upped the game that the M500t was dealing, besting it in all ways. But, to the Carver’s credit, I would not say the PA-7 embarrassed it: if anything, the Carver’s basic sound signature (*cough* Conrad Johnson *cough*) made a stretch towards the higher end, lacking primarily those last few levels of refinement and detail.

And power delivery…the PA-7 seems very effortless, where the M500t seemed to run out of gas sooner, despite both having similar power ratings. The PA-7 at higher levels does not sound as loud–perhaps because it is not straining. One startling aspect of the PA-7 is that it sounds as though a subwoofer is present. It does not boost the bass, but what I am noticing is how powerful the lowest bass notes are. The power reserves of this amplifier are able to deliver those low notes as intended. The M500t could come close at times, and often did, but at the lack of overusing the term, the PA-7 delivers this bass very effortlessly.

The Rotel? This is one of those rare instances where I will say the PA-7 kills the RB-1070 in just about every aspect. Even before the PA-7, I felt the Rotel to be rather unremarkable and bland, and anemic in power. I know it is rated at 130 w/ch vs. the Carver’s 251w/ch (and the PA-7’s 200w/ch), but still, that level of difference should have played out with just under a 3dB difference in volume. The Rotel just couldn’t keep up, and even at lower volumes it came across as being somewhat flat in dynamics. Not only that, I never felt the Rotel to be all that musical of an amp. Analytic? Maybe, if one is trying to be kind. More like bland and lifeless. I never enjoyed this amplifier. Some others have complained about the Rotel amps being bright. Yet I would not even say it was bright, yet that is one way I might explain its less than inviting midrange. It was…uninteresting. Not engaging at all; some nights, I couldn’t wait to turn the bloody thing off. That effortless bass quality was non-existent in this amp, and bass in general was anemic and, again, flat.

My next step is to replace the preamp. The Hafler DH-101 is no slouch (and is better since I recapped it recently), but I know I can improve on it. Audio Research is one such candidate–I like the SP-16 (primarily due to the remote), but may settle for a few of the others. Reportedly, the matching Nakamichi CA-7A control amplifier has fantastic sonics as well, although it is not a Nelson Pass design.

For now, I can say that the PA-7 certainly lives up to its reputation, and is worthy of a spot in any high-end system. Yet, it will not break the budget. If you are in the market for one, find one with good cosmetics–I have seen a few in less than stellar condition. To step up from this amp at its current price would probably require a tenfold increase in cost.

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