Demy,

Según HiFi Choice las diferencias entre el modelo básico del PM7200 y el KI son más bien pequeñas. Asimismo no encuentran diferencias al cambiar entre modo A y modo AB. Te transcribo la crítica completa:

Given the way we (and plenty of you, evidently) reacted to the basic, non-signature, PM7200, why on earth would Marantz want to upgrade it? Let's see: we accused it of having "bags of power... remarkable refinement... bass goes down for miles...". Okay, you get the idea. But we also pointed out that, bargain though it may be, it's not part of the real high-end pantheon.

So has Ken Ishiwata's signature on the front changed that? What, in fact, has he changed apart from the badge? Most obvious is the chassis, now entirely copper-plated inside and out. It's pretty and it's also functional, improving the conductivity of the metalwork and hence making it more effective at keeping interference out. Internally there are some component changes and a new toroidal mains transformer, entirely wrapped in copper foil to reduce electrostatic interference. Keeping with the theme, power transistors are also now covered with a copper-plated shield, and some internal wiring has been changed from stranded to solid core.

The biggest practical difference all these changes seem to make is to reduce the output power. Continuous output is just a little under 100 watts and peak output is around 110 watts, the former less than 1dB below the standard amp but the latter more like 2dB down. Put in those terms, it's not a big problem, and frankly you're still looking at a pretty powerful lump: it's also a little more assured into lower impedances so there is a quid pro quo. What may prove to be an issue is that hum is slightly increased compared with the standard model, at least on the review sample. This is almost certainly due to magnetic interference from the new transformer - copper foil doesn't do much about that, unfortunately. It's a buzzy,
high-frequency sort of hum on the left channel and with sensitive speakers it may just become audible at typical listening distances: however, the way toroidal transformers are made is inherently slightly inconsistent and levels of hum may vary between units.

In case you missed the original PM7200 review, here's a quick recap. This is an integrated amp with a fairly typical set of features - bypassable tone and balance controls, twin speaker outputs, plenty of inputs including phono and a remote control. But it also has unusually high power around the 100-watts mark plus the distinguishing feature of a choice of operating modes - high power Class AB or medium power (around 30 watts) Class A. In both original and KI units, Class A holds up to ten watts or a little under, so strictly speaking it's really highly enhanced Class AB. You can switch between the modes on the fly, which makes for fascinating comparisons, though in practice, at power levels within the Class A envelope, both we and at least one HFC correspondent found that differences are often so small as to make one wonder whether anything has changed.

Apart from the KI changes, construction is good inside and out but the casework is prone to resonance and a little damping wouldn't go amiss. This is easy for the user to experiment with of course, but if you're going to use Class A mode don't block up the ventilation slots! There's quite a lot of heat to get rid of and watching your hi-fi catch fire can seriously spoil a listening session...

SOUND QUALITY
It's been a while since the basic 7200 left HFC but luckily one such unit (not the one we reviewed) was also on hand for part of the listening tests, which reduced reliance on memory. At least one recollection proved correct: it's a very capable amp. Probably the toughest test of any true audiophile amp - high-power ones, anyway - is the extent to which it can fully take charge of any given speaker and show it who's the boss. That's also the area where budget amps have come on most obviously over the past decade or so, and while the 7200 isn't going to displace many Krells from their owners' affections it shows a lot more aptitude in that area than previous sub-£500 amps. Give it some high-energy programme in any musical genre and it will keep a tighter rein, with correspondingly tauter definition especially across the bottom couple of octaves, than one might expect from it.

It's probably in that department where the KI shows the most marked improvement over the basic 7200. And it's an interesting comparison too, not quite as simple as just being tauter or more extended. In fact it sometimes sounds less extended but that's not the actual case. What is actually happening, as becomes much clearer on extended listening and comparison with high-end references, is that the limits of the non-KI are being reached with some very tough basslines and its grip is relaxing just sufficiently to allow just a little bass bloat.
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