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March Audio - 1ET400A - P262 135w vs P422 227w


New Member
Jul 5, 2022
Hi All,

Bit of a newbie here and a bit confused, and understanding that this might get a bit technical. I am looking at a March Audio. Two options are the P262 and P422, with both, based on photos, running the 1ET400A chip. The 1ET400A is rated at 227w 8 ohm from the manufactuer, and across seemingly all other applications, however the P262 is outputting 135w. Would this be down to a less powerful power supply, and would limiting the chip in such a way reduce sound quality (March Audio does quote identical THD, but different signal to noise ratio), i'm not so concerned with the wattage itself as I listen nearfield and have quite sensitive speakers (Focal Chora 826), just curious if there'd be a noticable difference between the two.



Active Member
Jul 5, 2020
Cambridge, UK
The 1et400 is in fact a complete printed circuit board module supplied by Purifi to the majority of builders of these amplifiers (Exception NAD, a volume manufacturer, build their own using Purifi schematics).
The major difference between the March P262 and P422 is almost certainly just in the power supply Voltage and, possibly, current rating. The Purifi 1ET400 can output to within approx. 5V of its power rails. So with the nominal recommended supply of 65V we get approx 60V peak output or 225W into 8Ohm at approx. 1% THD . The 5V headroom ‘loss’ is likely to increase by a small amount as we lower the load impedance.
Most suppliers of the Purifi amplifier use a Hypex SMPS1200A400 +/-64V power supply which means their amps don’t quite make 225W but if you’re lucky enough to have 240V mains rather than 230V you’ll get your 225W as the SMPS1200A400 is unregulated and its output tracks mains supply.
March audio power supplies are no longer the SMPS1200A400 and the amplifiers work from 100-240V mains stabilised against supply changes. For the lower power P262 the power rail voltages are likely to be about +/-51V. The slightly reduced power into 2 Ohms (where the output isn’t voltage limited) might suggest that the power supply has marginally less current delivery than the supply for the P422 but this is rather insignificant.

EDIT: I didn’t address the issue of performance at power levels below the clip point in my original comments. I would think that the 2 amps would be identical. The residual noise is the same and the only difference is in the signal to noise ratio which is just a reflection of the increased maximum output of the P422 vs P262.
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