Pass X250 Owner's Manual Page 1
The X250 stereo amplifier embodies the design technology and refinements of the larger "X" series amplifiers including extensions of the patented Supersymmetry circuit. The Supersymmetry circuit topology was granted a U.S. patent in 1994, and is the result of 19 years of effort by Nelson Pass. The amplifier uses highly matched components in a classically simple balanced Class A circuit.
Setup You can position the amplifier anywhere you want, but it requires ventilation. We do not recommend placing it in enclosed cabinets or small closets without means for air to circulate freely. The amplifier idles at about 270 watts. Let’s talk about power requirements. The amplifier draws about 2.3 amps (continuous rms) out of the wall during normal audio operation, and this reflects mostly the idle current that we run through the output stage.
get fixed. We go to a lot of trouble to make products reliable, and the failure rate of our amplifiers is very low. This is small comfort to the few, but take it easy and give us a call if you have problems. People are interested in how long it takes for these amplifiers to break in. It takes about an hour for them to warm up, and this is where we adjust them first. Then we adjust them again and again over a couple of days, keeping the bias and offset in the sweet spot.
Interconnects and Speaker Cables We have a general recommendation about interconnects, which is that they should cost less than the amplifier. We have tried a lot of products and most of them work well, but as a practical matter we cannot make blanket recommendations. The amplifier is not sensitive to source interconnects. It is also not sensitive to radio frequency pickup, which allows some flexibility in choosing source interconnects without shields. We prefer speaker cables that are thick and short.
Warranty Information This product is warranted for parts and labor from the date we ship it. Check with the factory authorized distributor in the country you are purchasing this product for specific warranty information. Distributors are only required to offer warranty service on Pass products that they have sold. They are not obligated to offer warranty repair for products purchased from other distributors.
Once it was recognized that excessive use of negative feedback was creating problems with the sound, several designers addressed the problem by simply reducing the amount of feedback and regaining the performance by paying more attention to the character of the amplifying circuit itself. Feedback stopped being a “something for nothing” idea, and became more like a credit card, which is OK to use as long as you can afford to pay when the statement arrives.
Rushing to market in the 70’s with their low TIM distortion designs, companies employed either simpler or more complex circuits to achieve high slew rates. The amplifiers that had simpler circuits with fewer parts tended to sound better than the amplifiers with complex circuits and a lot of parts. They also cost less and broke down less often, not an unimportant benefit. Thus was a great principle of audio amplifier design reborn.
Supersymmetry does not reduce the distortion and noise present in either half of the output of the balanced circuit. Comparing the distortion curves before and after the application of supersymmetry, we see essentially no difference in either half of the balanced pair considered alone.
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 a series of amplifiers using the supersymmetric topology delivering up to 1000 watts per channel into 8 ohms with good distortion and noise figures.
intrinsic matching between the circuits, (c) the distortion of each half with supersymmetry, and (d) the differential distortion with supersymmetry. On this curve (B) we can clearly see that intrinsic symmetry due to the matching of the two halves reduces the distortion by a factor of 10. Supersymmetry (D) creates a more perfect match, and results in an additional reduction by a factor of 10.
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X250 distortion curve Page 13
X250 SPECIFICATIONS All figures obtained after 1 hour warmup, with regulated 120 VAC power line. See manual notes about AC power line regulation. Gain 30 dB Freq.
