All I could readily find is that the amp operates in pure class A up to 40 watts continuous into 8 ohms. It even allows for 80 watts peak in pure class A but converts to class A/B above that output. Most class A/B amps don't double down when the impedance halves but I think some do. Sorry for the non answer.

PASS LABS X250 Question

Hello, I am curious if anyone knows if the X250 Amp doubles its 8ohm rating when driven with a 4ohm loudspeaker. I don't see anything in the documentation that mentions this.

If it doesn't double it's output can anyone explain why this would be the case.

Thanks for any info you can provide

If it doesn't double it's output can anyone explain why this would be the case.

Thanks for any info you can provide

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- 14 posts total

I would feel pretty confident that the amp can supply 500W into 4 ohms, for the following reasons: 1)This review indicates that it can. 2)The first paragraph that starts on page 10 of the user manual sort of implies that it can. 3)The specs on the last page of the user manual indicate a maximum output voltage of 65 volts, and maximum output current of 20 amps. I believe those are peak numbers, rather than the conventionally used rms values. The rms equivalents for those numbers are 46 volts and 14.1 amps. 500 watts into 4 ohms requires 44.7 volts and 11.2 amps rms, those numbers being less than the specified capabilities. What is the input sensitivity for the X250 for full out-put, balanced and single-ended?The user manual indicates a gain of 30db. That is a voltage gain of about 31.6 times. 250W into 8 ohms, or 500W into 4 ohms, corresponds to an output of 44.7 volts. 44.7/31.6 = approximately 1.4 volts sensitivity (the input voltage required for maximum rated output power). That would apply to the unbalanced input. I suspect that an amplitude of 1.4 volts on each of the two signals at the balanced input (meaning a 2.8 volt differential) would also result in full power, but I'm not certain of that. The other possibility would be a 1.4 volt differential, or an amplitude of 0.7 volts for each of the two signals. Best regards, -- Al |

Pass amps are typically very unrated in power. My X150 amp puts out around 250 watts into 8 ohms and I think pushing 400 in 4 ohms. I don't doubt the X250 probably easily puts out 600-700 watts into 4ohms. I have never run out of steam with my X150 amp. This is on Eminent Tech speakers which are very inefficient. You should be fine. Plenty of head room with the X250 and I hear the X240 is the best sounding one of the bunch in that era prior to the .5 amps. |

I agree that X250 can easy output 400 watts rms into the load of 4 Ohms. I disagree with the calculation of the sensitivity. Almarg use relation between rms and peak in ....sinusoidal waveform which is not the case here. I cannot calculate exactly but I would take as a reference peak output current of 65 volts which should be slightly below rail voltage (65-70 volts) and then devide it over 31.6 times so it would seem to me that its sensitivity is 2 volts (go get its peak power whatever it is). Balanced input , in theory should be double indeed or about 4 volts. |

Michael, my calculation was based on the assumption that sensitivity is defined as the rms input voltage that is required to drive the amplifier to its maximum rated rms continous power output. I'm not 100% certain, but I believe that is the correct assumption. If I understand your post correctly, you appear to be assuming that sensitivity is defined as the instantaneous input voltage required to drive the amp's output to its maximum possible instantaneous output power level (the peak of a sine wave). That assumption strikes me as unlikely to be true, given that amplifier power ratings (and speaker power-handling ratings) are as far as I am aware always specified on an rms basis. Confusion sometimes arises due to loose usage of the term "peak." "Peak power" can refer to the power corresponding to the peak of a sinusoidal waveform, but it is also often used to refer to "MAXIMUM rms power." Regards, -- Al |

- 14 posts total