Hi Dan,
Thanks for the interesting links. Bob Cordell sure shares a lot of great information.
Interesting that he is also a big fan of HEXFET based MOSFET-style amps.
Since not everyone is an EE on the board (and just to be clear, neither am I, just more into EE-stuff than most), here are some ‘connect the dots’ thoughts:
As Bob points out, HEXFET’s can provide tons of current as compared to bipolar designs. Which means that when you take HEXFET output devices, and combine them the highly ingenious ‘tracking downconverter’ from the other Bob (Carver), we wind up with the Sunfire amps that can drive ultra-low impedance loads with ultra-high current and do so with very little wasted energy (‘ya know, Green is in
).
People with low-impedance speakers (i.e. all ESL owners) should read
Bob Carvers amplifier design white-paper.
Then think about the fact that you have current driven speakers, and think about your AB-class amp, and then realize you can’t actually supply the current your speakers really need. Time to re-think amp selection?
OK, those with Sanders ESL amps get a pass here, as those are well designed AB’s.
Also, Bob Cordell states that the role of an amplifier is:
It must multiply the incoming signal voltage by a factor of about 20, and deliver a perfect replica of the signal to the speaker, independent of the impedance that the speaker presents to it.
So, the amp must have ‘load invariant’ characteristics, which coincidentally, Sunfires have.
In the interview with Bob Cordell, he expresses many views which I subscribe to.
