I'm looking to get some Magnepan 1.7i. From what I've read, they are low sensitivity, like my KEF LS50 speaker. But they also apparently like high current to be at their best.

I'm looking at getting Purifi ET400a-based monoblocks. They are rated at about 425W into 4 Ohms and current is like 25A. These are supposed to be like the successor to the Hypex units. Now I know I'm on ASR and these amps should all sound the same, but for those who believe in audible differences I've heard that the Purifi is supposed to be even better sounding with improved soundstage and clarity.

The other option is Hypex NC1200-based monoblocks. They are rated at about 700W into 4 Ohms and current is like 40A.

Given the above, which is likely to get the best out of the Magnepan 1.7i speakers?

Thanks!

I have owned 6 pairs of Magnepans over 25 years, from SMGa's up to 3.5r. If I had a dollar for every time someone incorrectly said they require a lot of current, I would be rich. It is simply not true.

The easiest way to look at this is from the amplifier perspective. An amplifier is a voltage device. In response to a set input from the preamplifier, the amplifier outputs a set voltage. This continues until the amplifier in unable to supply sufficient current to maintain the voltage and starts to clip. Ohm's law dictates the required current, it doubles from 8 ohms to 4 ohms and again into 2 ohms. The only fly in the ointment is that speakers with a high phase angle can require more current than a straight Ohm's law calculation would show.

In the case of Magnepans, they are almost a perfect resistive 4 ohm load with low phase angles. Some drop to 3 ohms, but not at low frequencies where the most power is needed. Lets run some quick calculations:

Purifi 1ET400- 425w into 4 ohms- This is 41.2 volts and 10.3 amps of current. At 3 ohms to maintain the same voltage the amplifier would have to put out 13.7 amps which would net 565 watts. The Purifi is rated at 25 amps of current.

Ncore NC1200- 700w into 4 ohms- This is 53 volts and 13.2 amps. At 3 ohms to maintain the same voltage you are at 17.6 amps which nets 933 watts. The NC1200 is rated at 40A peak current and its limiter cuts in at 38 amps.

As you can see, Magnepans are not getting close to the limit of the current capabilities of either of these amplifiers. Any amplifier that is designed to drive a 4 ohm load will comfortably supply enough current for Magnepans.

The real issue, as you point out, is that Magnepans have low efficiency and require a lot of voltage (e.g. watts). The question is how loud do you listen and how large is your room? I know with my 3.5s and 700 watts to each (high passed at 80hz), they could only put out about 102db peak in my room (which is loud, but not extremely loud). There is only so much output the panels are capable of.

In most cases, the Purifi will have enough power for the 1.7s. Going to the NC1200s will net you 2 db more output, if the 1.7s are capable of actually putting out more output. In terms of quality, the Purifi measures a bit better, but both the Ncore amps and Purifi measure better than the limits of a 16 bit recording and the differences are likely inaudible. So the question is do you want excellent measurements or really excellent measurements?