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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.  If you are driving a low impedance load, you will draw more than
this, but this will not be typical.

The X250 is provided 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 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 connectors 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 charges 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, don’t get excited,
just use the front panel stand-by button to go to stand-by mode, with the "Standby" LED on
and the "Power " LED 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 place (between pins 1 & 3 on the XLR).

Now that the source component is connected, make sure there is no signal coming from it,
probably by turning the volume all the way down.

With the speakers connected, push the front panel button to activate the amplifier.  The
"Power" LED will come on.

You are ready to play music.

Do everybody a favor and try not to have shorted output cables.  It happens accidentally all the
time, and the amplifier is designed to survive, but I wouldn’t bet the farm on it.

Of course it’s always possible that something could go wrong.  If so, don’t get excited, just
relax.  It’s really aggravating when something like this doesn’t work, we understand, but it will

Summary of Contents for Pass X250

Page 1: ...Page 1 Pass X250 Owner s Manual ...

Page 2: ...ing a gain stage an inversely distorted signal Supersymmetry seeks merely 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 distortion of a conventionally simple a...

Page 3: ...ure 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 charges 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 don t get excited just use th...

Page 4: ...l button so if you want the button to operate leave the rear connection open So much for the most essential information Speaker Interface The X250 is optimized for loads nominally rated at 4 ohms and above You can run the amplifiers into a lower nominal impedance without difficulty and we are not aware of a speaker on the market that presents unusual difficulty with these amplifiers The X amplifie...

Page 5: ...s each These are used to create the unregulated output stage rails at plus and minus 47 volts at 20 amps All the power transistors in the product are power Mosfets actually Hexfets from International Rectifier and Harris These are hyper matched parts with gate voltages matched to 0 5 and all devices taken from the same lot codes made on the same wafer The speed and noise critical gain devices in t...

Page 6: ...have been offered during this century but the ideas that have stood the test of time have delivered much better performance in simple ways Two of the best ideas have been negative feedback and push pull operation Negative feedback is a simple technique which requires only a couple more parts arranged simply but it achieves dramatic improvements in performance Similarly for push pull operation a co...

Page 7: ... much in wasted energy but in the cost of the heavier hardware needed to deliver and dissipate the additional heat One of the important potential advantages of Class A operation is the possibility for simplified circuitry requiring little or no feedback because of the much more linear performance of gain devices biased to a high current By the mid 1970 s the marketplace began to see high end solid...

Page 8: ...my part led to the Stasis amplifier a simpler if cruder circuit in which the ocean liner could just about make it into port by itself with only minor damage and the tugboat was capable of crossing the Atlantic if not the Pacific Threshold and Nakamichi have sold lots of these amplifiers for the last 19 years or so and so it was pretty successful Yet it was always in the back of my head that there ...

Page 9: ...I decided to build a state of the art very high power amplifier the X1000 a project not particularly appropriate for the single ended Class A approach believe me you don t 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 potential circuits revealed that the best topology for the front end of the ampli...

Page 10: ... 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 one 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 dis...

Page 11: ... the two halves of the circuit and 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 balanced gain stage The following pages include a typical distortion curve of ...

Page 12: ... Current plus minus 20 amps Input Impedance 22 kohm balanced Damping factor 250 ref 8 ohms nominal Slew rate plus minus 50 V uS Output Noise 300 uV unweighted 20 20 kHz Random noise floor approximately 2 uV Dynamic range 148 dB random noise floor to peak output Balanced CMRR 85 dB 1 kHz input common mode rejection ratio DC offset 100 mv Power Consumption 270 watts idle 1000 watts maximum Temperatu...

Page 13: ...Page 13 tel 530 367 3690 fax 530 367 2193 ...

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