PASS LABS X250 Question

Hi Mike,

I suspect that the 100 volt figure you are thinking of is peak-to-peak, not peak. Note in the manual that the maximum output voltage spec of the X250 is indicated as "plus, minus 65 volts," the 65V therefore obviously being peak, rather than peak-to-peak.

100V peak-to-peak corresponds to about 156 watts rms into 8 ohms, or 312W rms into 4 ohms, and would be well within the X250's peak-to-peak voltage swing capability of 65 x 2 = 130 volts.

Based on that voltage swing capability, as you will realize it can readily be calculated that the amp will not clip until an output power level of 264W rms (or more) into 8 ohms is reached, or 528W rms (or more) into 4 ohms.

Best regards,
-- Al

Al, thanks again.

Hello Al,

I meant +/-100 volts... I took this number from Spectron web site:

"...in reality an amplifier's voltage headroom is limited by the power supply voltage, which limits the peak voltage. Spectron's amplifiers are the highest voltage we know of in the audiophile world, using a plus and minus supply of 120V. By comparison most amplifiers use power supply voltages on the order of plus and minus 85V or even lower. An engineer evaluating an amplifier to determine the required headroom would look at the output voltage of the amplifier with an oscilloscope while playing the loudest music he would reasonably anticipate would be listened to. At Spectron we have done that. What we see is that it is common in high quality recordings to see voltages near 100V peak, with medium efficiency speakers. This means that when listening to the same music with most other amplifiers, the signal would be 'clipped'... "

What we see is that it is common in high quality recordings to see voltages near 100V peak, with medium efficiency speakers. This means that when listening to the same music with most other amplifiers, the signal would be 'clipped'... "

Hi Mike,

I wouldn't take that statement too seriously. If it were true, most people would be experiencing intolerable clipping much of the time.

100V peak (200V peak-to-peak) is 625 watts rms into 8 ohms, or 1250 watts rms into 4 ohms. That would blow up many home speakers even if applied very briefly. And, using 90db/1W/1m 8 ohm non-planar speakers as an example of "medium efficiency speakers," 625 watts would correspond to a sound pressure level of around 112db at a listening distance of 10 feet.

Accurately reproducing the cannon shots on Telarc's notorious recording of the "1812 Overture" might require that, but I would expect that not much else will.

Best regards,
-- Al

Hey Thanks to everyone for the information. It has been very interesting to read.

Based on what I have read here I feel pretty confident now that the Amp can most likely double it's 8ohm rating without much fuss. I may shoot Nelson Pass an email just out of further curiosity.

One thing that I found interesting about this Amp is how much cooler it runs when plugged into a dedicated Power Conditioner. This is something I recently noticed when switching from a Shared Power Conditioner configuration and the info posted here relating to Power Supply capabilities of the various Amps basically confirms what I have noticed on my own Amp.

The thing that I found most surprising about the temperature differences of the two configurations is that it wasn't like I was using a small Power Conditioner to begin with (it's a Shunyata V-Ray). My previous configuration also consisted of 1 x dedicated 20amp circuit, 10 ga Romex wiring to the breaker box and a full host of Shunyata power cords (20 amp Python from the wall to the V-Ray & 15amp Taipan to the Amp).

The new configuration includes an additional 20 amp Python and a Shunyata Hydra 6 on a second 20 amp circuit that only runs the Pass X250.

Temperature wise it's a huge difference going from almost not being able to touch the top of the Amp to a luke warm after a full nights listening session at an aggressive volume.

So it seems that it is a very hungry beast and is much happier with its own supply of juice. All in all, it definitely has plenty of headroom in my system even if it didn't double its 8ohm rating.

Thanks again for the info