Pass X250 Manual 电路图.pdf

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1、 Page 1 Pass X250 Owners Manual RadioFans.CN 收音机爱 好者资料库 Page 2 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,

2、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. The amplifier contains only two simple stages: the first is a balanced Class A voltage gain stage using low noise Jfet input devices followed by comp

3、lementary Mosfets. Its output drives a bank of high power Mosfets operated as voltage followers. These are inherently low distortion types of circuits, but their performance is improved when operated in balanced mode through cancellation. Distortion and noise identical to both halves of a balanced c

4、ircuit will disappear at the output, and in a well-matched symmetric circuit, most of the distortion and noise is identical. Supersymmetry enhances this effect by providing a connection between the two halves of the balanced circuit that further perfects the match. Any distortion and noise not alrea

5、dy identical to the two halves is made identical through feedback by a factor of about 10, and the result is improved cancellation at the output. Unlike feedback techniques where the goal is to correct for the distortion by feeding a gain stage an inversely distorted signal, Supersymmetry seeks mere

6、ly to create perfect matching. Matched balanced power circuitry typically sees a distortion and noise reduction of about 90% (20 dB) through a balanced connection without any additional effort. The Supersymmetric circuit delivers another 90% reduction, so that the X series has about 1/100 of the dis

7、tortion of a conventionally simple amplifier. Actually this ordinary distortion and noise can still be seen at the output of one half of the circuit, but since it is virtually identical on the other half, it goes away at the speaker terminals. This gives good measured performance, which because it i

8、s produced by a simple circuit, also sounds excellent. Previously these kinds of simple Class A circuits have been popular for their sound quality in low power amplifiers, but have not found application at high power levels due to excessive distortion and low efficiency. Supersymmetry overcomes this

9、 barrier, delivering the sweetness, staging, and detail of very simple circuitry up to kilowatt power levels and beyond. The X Series amplifiers have the tremendous dynamic range (150 dB) to do justice to the 24 bit recordings of the 21st Century. The simple but powerful circuitry moves easily from

10、total silence to explosive transient and back to silence without a trace. So relax and enjoy your amplifier. Call us if you ever have a problem or question. Nelson personally answers his email addressed to , and you are welcome to ask questions or offer comments. Thank you for buying our product. Ra

11、dioFans.CN 收音机爱 好者资料库 Page 3 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. Lets talk about power requirements

12、. 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. If you are driving a low impedance load, you will draw more than this, but this will not be typical. The X250 is provid

13、ed with the more conventional AC line cord, which is rated at 15 amps. The circuit ground is attached to the chassis in the conventional manner. The power input to the amplifier runs through a 3 pole RF filter which removes high frequency noise coming into and going out of the power supply. Under no

14、 circumstances should you defeat the ground connection of the power cord. For your safety, the chassis of the amplifier should be earth grounded. Looking at the rear panel you will see the AC power cord receptacle, a power switch, fuse holder, two pairs of output connectors, a pair of 5 way connecto

15、rs for remote turn-on, two RCA input connectors and two XLR balanced input connectors. Make sure that the power switch is off (down). Plug the AC cord into the back of the amplifier, and then into the wall. Then turn the switch on (up). The lights in your house will blink when the power supply charg

16、es the capacitors. On the front panel, the Standby LED indicator should be glowing blue, indicating that the power is on. The Power LED should not be on. If the Power LED is on, dont get excited, just use the front panel stand-by button to go to stand-by mode, with the Standby LED on and the Power L

17、ED off. OK, so the amplifier is sitting there in stand-by mode with just the single blue LED lit. No speaker connected yet. You can go ahead and connect the source and speakers. The amplifier can be driven single-end or balanced, if driving the amplifier single-ended leave the supplied jumpers in pl

18、ace (between pins 1 it must be driven by a balanced input signal and it only produces a balanced output signal. You could drive it with a single-ended input and hook a speaker up to only one output and ground, but there would be no point to it at all. Supersymmetry operates to make the two halves of

19、 the balanced circuit behave absolutely identically. Constructing the two halves of the circuit with identical topologies and matching the components precisely achieves a 20 dB or so reduction in distortion and noise, and local feedback with a Supersymmetric connection another 20 dB or so. This is e

20、asily 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 sta

21、ges, 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 simpl

22、e enough approach, although I didnt 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 single-ended Class A amplifiers. In 1997 I decided to build a state-of-th

23、e-art very high power amplifier, the X1000, a project not particularly appropriate for the single-ended Class A approach (believe me, you dont want to own an amplifier idling at 3000 watts per channel). So I pulled out the files on patent # 5,376,899 and took another look. Extensive testing of poten

24、tial circuits revealed that the best topology for the front end of the amplifier is what we refer to as “balanced single-ended”, a phrase I use to refer to differential use of two single-ended Class A gain devices. The classic differential pair of transistors (or tubes, for that matter) is just such

25、 a topology. “Balanced single-ended” is an oxymoron in the sense that most single-ended enthusiasts believe that the most desirable characteristic of single-ended circuits is their generation of even-order distortion components by virtue of their asymmetry. Purists will point out that a balanced ver

26、sion of a single-ended circuit will experience cancellation of noise and even-order components. Just so. Interestingly, the single-ended nature of each half of the balanced circuit doesnt give rise to much in the way of odd-order distortion, and when the even-order components and noise are cancelled

27、 there isnt much distortion and noise left. In any case, “Balanced single-ended” is a phrase that accurately describes the circuit. For the amplifiers front end, a balanced single-ended gain stage was developed which used just a differential pair of Mosfet gain devices. These were biased by constant

28、 current sources and cascoded for maximum performance and given local feedback and a Supersymmetric connection. After years of trying alternative arrangements, it ended up virtually identical to the schematic on the cover page of the patent, which is reproduced later in this manual. The front end, w

29、hich 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 Page 10 ultimately we found that w

30、e 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 us

31、ing the supersymmetric topology delivering up 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. People inevitably will ask

32、 how this relates to bridged amplifiers in general, and the balanced amplifier offerings of other companies. It is similar in that both terminals of the output to the speaker are “live”; neither of them is grounded. The supersymmetric amplifier is a special subset of balanced amplifiers, unique and

33、covered by U.S. patent. Supersymmetry is an approach that truly takes advantage of balanced operation like no other and requires a balanced input to retain the precisely matched behavior. Supersymmetry is ideally used to obtain high quality performance from very simple circuit topologies, avoiding t

34、he high order distortion character and feedback instabilities of complex circuits. A single gain stage amplifier using this approach can perform as well as a two gain stage design, and a two gain stage version of this topology can outperform the four or five stages of a conventional amplifier. Here

35、is some more explanation of the details of its operation: The supersymmetry topology does not use operational amplifiers as building blocks, nor can it be represented with operational amplifiers. It has two negative inputs and two positive outputs and consists of two matched gain blocks coupled at o

36、ne central point where the voltage is ideally zero. The topology is unique in that at this point, the distortion contributed by each half appears out of phase with the signal, and we use this to reinforce the desired signal and cancel noise and distortion. This occurs mutually between the two halves

37、 of the circuit, and the result is signal symmetry with respect to both the voltage and current axis, and anti- symmetry for distortion and noise. This means that the distortion and noise of each half appears identically and cancels. The diagram on the patent cover sheet shows an example of this top

38、ology. Each of the two input devices 20 and 21 are driven by an input signal, and their outputs run through a folded cascode formed by devices 30 and 31 to develop voltages across current sources 34 and 35. The sources 20 and 21 are coupled through resistor 40 which is the sole connection between th

39、e two halves and which also sets the gain of the circuit. The gates of the input devices 20, 21 are virtual grounds, and ideally would be at absolutely zero voltage. However, as the gain stage is not perfect, finite distortion and noise voltages appear at these points. These appear at the other side

40、 through resistor 40, in phase at the output of the other half of the system, where they match the distortion and noise of the first half. By actual measurement, this circuit does essentially nothing to reduce the distortion and noise in each half. Distortion curves before and after supersymmetry is

41、 applied are nearly identical. The distortion curves of the circuit from the patent cover sheet show: (a) the intrinsic distortion of each half of the example circuit, (b) the distortion of the differential output lowered due to the Page 11 intrinsic matching between the circuits, (c) the distortion

42、 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 add

43、itional reduction by a factor of 10. However there is essentially no difference in the distortion figures at the output (C) of each half of the circuit considered alone. Supersymmetry does not work by reducing the distortion per se, rather it works to precisely match the two halves of the circuit an

44、d lets the balanced output ignore the unwanted components. As long as the two halves are matched, this performance tends to be frequency independent, and does not deteriorate over the audio band. With mid-level distortion figures on the order of .002%, this is very high performance for a single bala

45、nced gain stage. The following pages include, a typical distortion curve of the amplifier, a list of specifications for the amplifier, and where to reach us. If you have questions, or we can help you, please feel free to contact us. Again, you can easily contact Nelson Pass by email addressed to , a

46、nd you are welcome to ask questions or offer comments. Other personnel are available through the website , as are copies of patents, DIY articles, and product information. Page 12 X250 SPECIFICATIONS All figures obtained after 1 hour warmup, with regulated 120 VAC power line. See manual notes about

47、AC power line regulation. Gain30 dB Freq. Response-0 dB at DC, -3 dB at 100 kHz Power Output250 watts maximum 1% THD, 1 kHz, 8 ohms Distortionrefer to accompanying distortion curve Maximum Output Voltageplus, minus 65 volts Maximum Output Currentplus, minus 20 amps Input Impedance22 kohm balanced Da

48、mping factor250 ref 8 ohms nominal Slew rateplus, minus 50 V/uS Output Noise300 uV unweighted 20-20 kHz Random noise floorapproximately 2 uV Dynamic range148 dB (random noise floor to peak output) Balanced CMRR-85 dB 1 kHz (input common mode rejection ratio) DC offset 100 mv Power Consumption270 watts idle, 1000 watts maximum Temperature20 degrees C. above ambient at idle Dimensions19 W x 22 D x 9.5 H Shipping Weight100 lbs. PASSPASS Pass Labs PO Box 12878 Reno NV 89510-2878 Page 13 tel:(530) 367 3690 fax:(530) 367 2193