feedback with a Supersymmetric connection another 20 dB or so. This is easily accomplished with only one gain stage instead of the multiple stages required by conventional design, and so it results in only one “pole” of high frequency characteristic, and is unconditionally stable without compensation. In fact, if you build a supersymmetric circuit with multiple gain stages, it does not work as well.
In 1993 I attempted to build the first power amplifier using this principle, but it was not successful. Ironically, the supersymmetric concept not only allows for very simple gain circuits, but it requires them for good performance. My first efforts did not use a simple enough approach, although I didn’t realize it at the time. A more modest version of the circuit found its way into a preamplifier, the Aleph P. Ultimately the power amplifier was set aside, as we were very busy building Aleph
In 1997 Pass Labs decided to build a
“Balanced
For the amplifier’s front end, a balanced
The front end, which develops all the voltage gain for the amplifier, then presents this voltage to a large bank of follower Mosfet power transistors. Originally it was assumed that we would have to enclose this output stage in a feedback loop to get the performance we wanted, but ultimately we found that we could operate it without feedback as long as we put a healthy bias current through it. For these amplifiers this is about 600 watts worth. This is not pure Class A operation in the context of 1000 watts output, but it has proven to be the appropriate amount.
The result is three amplifiers using the supersymmetric topology delivering from 350 to 1000 watts per channel into 8 ohms with good distortion and noise figures. If you are a little less fussy about distortion, you will get twice that into 4 ohms. This is accomplished with only two gain stages and no feedback.
You want more? We can do that, too. The X1000 can be operated in series and parallel arrays to present multiple values of voltage and current so as to create a huge power/performance envelope direct coupled into virtually any load.
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