Nuforce STA200

"At 51K ohms input impedance and the high input sensitivity a good candidate for a passive..."

The 0.45V input sensitivity is not much of an issue, its actually relatively low, but the 35dB gain is more of a concern. A passive with a low output impedance may work depending on the output voltage of the source.

Kalali, if my understanding is correct, because the voltage required to reach max output is low, sensitivity is high.  Given the output voltage of most sources today, the sensitivity and gain of this amp would call for judicious use of the volume control of any preamp. I have not yet approached 11 o-clock with my SYS passive.

Jetter, not knowing any more about the specifics of aysancorluham's situation it is hard to guess at why his amp 'blew up'. I would be cautious about using this amp with any speaker not known to be easily driven by an amplifier. To me that mean a speaker that doesn't dip below 6 ohms across the frequency range, and having a sensitivity of 87dB or higher depending on the size of the room in which the system is to be used.  

Finding such a speaker, one I feel fits into a budget commensurate to a $500 amplifier and $50 passive, is the difficult part. I am still looking.  

Mesch, I have two pairs of nominal 6 ohm speakers, both probably in the 85db range.  One is a 2&1/2 way with two 7 1/2" or so scanspeak mid/woofers.  I can run the unit all day, with the STA200, being fed by this tube preamp, http://www.divertech.com/coplandcta305.html and the amp never is even warm to the touch.  I have a Schitt sys, but honestly it is set to not reduce the output to the amp at all as it is not needed.  In other words, the volume control can be turned up far enough (high enough) from the zero position with the sys in or out of the system to not worry about the preamp volume control not being high enough to function fully.  I don't understand the impedance matching thing to know if I happen to have a more compatible preamp than normal or what.

Well, I might just be overly cautious. I need to spend more time with my STA200. I certainly am happy with it's sonics and it seems compatible with my PS Audio Digital Link III via the SYS. In addition to the speakers I mentioned earlier, I also have a pair of Dali Zensor 1s which don't drop lower that 5ohms and are 88dB sensitive. I will try the amp with these as well. 

I purchased this amp for use with a passive pre in an attempt to build a low cost high quality system.  Though I don't believe specs tell the whole story, I do believe there are some that certainly help to insure electronic compatibility between components when putting together a system. I have learned much from this forum toward that end. I remain with much more to learn.

Happy New Year to all!

Thanks mesch for your clarification, truly appreciated.  From your earlier post I got the mistaken impression that you were saying that you knew of an identified amplifier design weakness that could result in possible serious amp failure.  I don't think this any longer.  These things do happen though, for example, I have a pair of Goertz alpha core speaker cables that without the use of zobel networks have resulted in some amps going into oscillation with not pretty results.

So blue skies on this end.