First Watt: current vs voltage

However, in man places I read that First Watt are current amps (in opposed to voltage amps) and thus they can only be used with single drivers speakers.

this makes no sense at all!! How did you conclude the 2nd part of your sentence from the first part??
Liguy has basically hit the nail on the head - all First Watt amps are power amplifiers. The First Watt amps seem to be low wattage, high(er) current amps made with a certain type of speaker load in mind (& that speaker load seems to be what I would call a benign load i.e. load impedance remains fairly flat 20Hz-20KHz & the phase shifts in that same freq range are minimal & not wild excursions from positive to negative & vice-versa).
I have a feeling, like Liguy, that the exclusive single-driver application being touted comes from the fact that single-driver speakers (which have no xover if there is no super tweeter) are benign loads. These amps should be able to drive any benign load speaker.

Liguy and bombay walla,

Have you actually looked at the details and reviews of the F1 and F2? These are unique designs that do not work with speakers with crossovers. If you want to contradict Nelson Pass, fine by me. But take a look at the designs and the manuals and schematics that First Watt provides, or read the reviews which also explain this.

Thanks, Guys!!! I have read the 6moons reviews, but somehow missed that only F1 and F2 were current sources.

Liguy and bombay walla, your argument makes sense to me. However, I know very little about electrical engineer. :-) I trust people who actually know when they say the current source amp do not work with cross-overs.

Liguy gives a great explanation of what the First Watt amps are about. Circling back to the original question, except for the F1 and F2, the big limitation with First Watt amps is their power output, which tops out at about 25 watts per channel, with no additional headroom, depending on model. I have an Aleph J, which is a wonderful amp, and which drives my very conventional, not-single-driver, loudspeakers to reasonable levels. Nelson Pass designs actually do sound different, and IMHO better, than many other amps. If you play music at moderate levels, you'll probably never notice the power limitation. I attached a power meter to the Aleph J and have never needed an output above 15 watts, peak. But note that my system is in a relatively small room.

I second the suggestion that you talk to Mark at Reno Hi-Fi, who can probably suggest the right First Watt amp to compliment your system.

Here is the recommended xover types for current amps:
http://www.firstwatt.com/pdf/art_cs_xvrs.pdf
It is not mandatory to use such these. You may get good results with other types.