In order to sort of establish a baseline, I switched things around a bit in order to keep the h/k's in the rack for a short while. I moved the B-2X off the rack entirely, and ran three sets of cables to the speakers. Because I normally run 4 amplifiers, I have two runs of cable already (12-ft of 11-ga. Ixos Gamma Geometry for bass, and a 16-ft run of Zu Audio Libtec). The third run was for the Yamaha and consisted of a high quality 12-ga. stranded cable, about 10-ft in length. When run full range, the two sets of jacks on the speakers are jumper'd with a bit of pure copper bus bar.
To sort of condition myself, and to help to accurately note differences, I setup the system in three different ways- first was how I normally run it, with the 4 h/k's. The second configuration was with the Yamaha, and the third configuration was with a solo set of h/k's, with the same 12-ga. cable as was to be used with the Yamaha.
First, I'd like to comment a bit about the construction and some of the details of the Yamaha B-2X for those who may be unfamiliar with this amp. Starting in the mid-1970's, Yamaha latched on to the then still burgeoning idea of Class A solid-state amps. Models such as the CA-1000, CA-1010, and others featured a Class A operation option, which gave up power and economy in exchange for a 10's or dozens of watts of Class A power. This is a feature that continued through the 1980's, and there are more than a few Yamaha amps (integrated or power amps) that have switchable Class A operation. Some others, however, featured Class A operation as a matter of design, seamlessly shifting gears from a low-powered Class A amplifier to a higher powered, more typical Class AB amp. The B-2X is one of those amps. Novel, somewhat, to Yamaha was the actual execution of this Class A/AB design. Some companies used what has been coined "sliding bias", where a circuit follows the input signal and adjusts the bias of the output stage so that it is always "technically" running in Class A, at least to a point. Others used parallel output stages, one operating in Class A, with the other operating as a typical Class AB/B amp. Yamaha's approach (and one that would be used as the basis for their "HCA" design in the MX-10000) was to sort of bridge an independent Class A output stage with a more traditional Class AB output stage. In essence, the Class AB stage acted like a reverse/mirrored load, providing current through the real load (the speaker) to keep the voltage across the Class A stage constant. This meant that all the class A stage had to do is provide voltage (with no real load) and thus, theoretically, could provide Class A operation through to full output. For this reason, unlike many amplifiers, the (-) terminal is not, in fact, connected to the chassis ground, but is instead connected to the output of the Class A amplifier. The (+) terminal is connected to the output of the Class AB amp in more standard fashion. This novel approach to Class A operation aside, the amp is noteworthy for other details. The unit is twin powered, with each channel having its own ~450VA power transformer, twin 22,000uFd caps for storage, (twin 100kFd(!) caps for the class A filter), and build quality and construction that would rival any higher-end amp today. The one sore point, in my view, are the speaker terminals. In theory, the best speaker connector is none at all; that is, when it comes to banana's v. spades v. pins v. bare wire, bare wire is, in theory, superior. In practice, however, bare wire can be unwieldy, and is hardly convenient, especially for those like me that have frequent occasion to swap gear. That said, the terminals used by Yamaha are, in theory, superior to what I'm accustomed to using with my h/k's, but I was not willing to lob the ends off my quite expensive cables to accommodate the Yamaha.
So on to a bit of listening. After I had gone through the three setups listed above to sort of establish a starting point, I put the B-2X back in the rack and allowed it to idle for about an hour. The first disc I listened to after the amp had a chance to cook was a mix disc of various trip-hop and electronica type music (Massive Attack, Sneaker Pimps, and the like). I found more similarities between the h/k setup and the Yamaha than differences. Where there are differences, they're quite subtle, and are not a reflection of either amp doing anything wrong, but rather doing it right, just differently. Overall, the B-2X seems a little softer in presentation, somewhat more akin to an amp that makes use of FET's (MOSFETs or JFETs). In particular, in some instances where the h/k's reproduced a sibilance, the B-2X slightly glossed it over with a bit of harmonic glassiness (like a stronger than normal 2nd harmonic added to the fundamental "s" sound). That's certainly not a problem, but it does tend to make me think that the h/k's are more technically accurate, while the Yamaha is slightly more musically pleasing. Bass is the other area where there is some difference. The bass from the Yamaha seems to be a little more well damped and tighter. Playing a track with a bit of kick-drum has a bit more initial impact and quicker decay than with the h/k's, meaning that on the low-end, their accuracy v. musicality swaps places. Still, on other tracks, they're neck and neck in terms of impact and definition. Indeed, I would be hard pressed with most music to tell which amp was which in a blind test. This is a very good thing for the Yamaha.
But now that I have some comparisons and base-level listening done, the Yamaha will be continued to be used on its own throughout the rest of the week, at least, and will ultimately be judged based on its own merit, and not how well it compares with my normal amps. But, if the first couple hours are any indication, it should prove to be a great amp and a very enjoyable week.
