First Watt: current vs voltage

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.

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Liguy and Bombay, you are incorrect. There is a night and day difference in the way current and voltage source amps operate. They are not just power amps.

Some of the First Watt are current source amps and some are the more common voltage source amps. I think Mr. Pass screwed up to mix the two topologies in one line of amps since it leads to confusion like this.

The current source models will not work with most speakers. They are not the equivalent of SET tube amps as the latter are voltage source amps. The need to use them with single drivers has no relationship to the fact that most of these speakers are efficient even though being lower power does make a good match with them.

From the F1 manual

"This is a very unusual amplifier that will not sound good with about 98% of the loudspeakers on the market. It requires careful attention to loudspeaker loading to get the best performance.

It does not work well with ordinary passive crossover networks – the components and their locations tend to be reversed. It won’t break, but probably won’t sound good."

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