First Watt: current vs voltage

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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A current source amplifier has a very high output impedance- usually multiples of the speaker impedance.

A voltage source amplifier has a low output impedance, usually a small fraction of the speaker impedance.

Either one can sound good, but as far as what speakers work with them has to do with the speaker manufacturer's intention- whether the speaker is designed to work with voltage source amplifiers, power source amplifiers (tubes) or current source amplifiers (usually the latter employ some sort of current feedback which increases the output impedance).

The issue is two-fold: first, the crossover frequencies may not work right as the way these amplifiers behave is very different (an example here is using horns with voltage source amplifiers often results on horns that honk, due to the crossover not working correctly with the voltage source amplifier), and then if there is a port or other means of dealing with the box resonance, that may not work right for the same reason.

This is why equipment matching between amps and speakers is an on-going conversation in high end audio. Now if the speaker is OK with SET amplifiers, it stands a good chance of also working with a current source amplifier. So in this case its worth an audition- see what you think!

I have always seen voltage source attached to amplifiers that are capable of a high output in amps and can increasing their output into lower impedence loads. IE Krell is a voltage source amp, a Quad 405 isn't.At least this is the usage in England that I have seen in reading HF mags the last 40 years.

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Stan, sort of.

For a given input voltage an ideal voltage source will maintain a constant output voltage no matter what the load i.e. no matter how low the load impedance goes and no matter how much current the load draws. This requires the amp to have extremely low output impedance, ideally zero. Monstrous power amps like Krells are closer to these ideals than the Quad but they are both considered voltage sources.

Current sources are an entirely different beast.

For a given input voltage an ideal current source will maintain a constant output current no matter what the load. This requires the amp to have extremely high output impedance, ideally infinite. The First Watts are not that high with an output impedance around 80 ohms but that is 10 times most loads so they act more like current sources.

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