Tubes and less sensitive speakers

Magnepans are typically very inefficient and require high current amps to get the best out of them. 

@jeffbij Just so you know, this statement is false. 

To understand why the first thing you need to know is how current plays out in a speaker like this, which is a fairly resistive four Ohms without odd phase angles.

To make 200 Watts into that speaker you need an amp that can make just a tiny bit over 7 Amps. As you probably know, in the scheme of solid state amps that's not a lot of current.

A 'high current' amp is probably called that because it can double power into 4 Ohms from 8 and maybe again from 4 Ohms down to 2 Ohms. But the Maggies really don't require an amp that can drive 2 Ohms with double the power. They only require that the amp make power into 4 Ohms and can do it in such a way that very minor variations in impedance don't result in variations in output.

Many so-called 'high current' amps advertise a current rating that doesn't square with the power ratings they claim; IOW the 'current' stated is often far more than the amp could ever produce. That is because that rating is the amount of current that would flow for 10milliseconds if the power supply were shorted out. Its not anything to do with the power the amp can make.

Since the speakers don't have a box, they don't have the same sort of resonance that requires a low output impedance to control them, even in the bass. They just need the amp to be able to make the power.

It is true Maggies don't seem to be very efficient. But since they behave as a line source, you really have to add about 6dB to their measurement to understand what is going on. If you've been around a set of Maggies, you may have noticed that they sound just as loud ten feet away as they do when you are only a foot away. That is because at a distance, more of the output of the speaker is reaching your ears while when close up it does not. The same is true of a microphone placed 1 meter from them.

So this means the speaker really is more sensitive than the rating suggests. The model 2.7i for example is similar to an 8 Ohm box speaker of 89dB or a 4 Ohm speaker that is 92dB.

Crazy Suggestion since they are hard to find and long out of production but perhaps the 400 watt Melos monoblocks(triode output). They easily put out 400 watts(under rated, especially earlier versions) with a relatively high damping factor too(20 if I recall). The big problem is taking care of them and rare tubes(EL519).

@atmasphere  -  I stand corrected.  I've always based my efficieny for Maggies on their published specs, but the reasoning about the line source behavior makes sense.  I even took a moment to test the

...they sound just as loud ten feet away as they do when you are only a foot away.

and I agree.  In my ~20 years of Maggies in my secondary system, it was something that I never paid attention to.

Just goes to show, we can always learn something new every day.

One thing to consider is installing a high pass filter on the input jacks of the power amp (inside the amp)---or in a little box containing the filter plugged into the input jacks (as the video below will explain)---feeding the Maggies, to remove low bass frequencies from entering the amp and therefore the Maggies. The "corner" frequency of the filter is determined by the value of the capacitor used and the input impedance of the amp. There are formulas available on the internet for determining the cap value required for different amplifier input frequencies and the desired x/o frequency. Removing the low bass from the input signal to the amp will significantly decrease the power required to run the Maggies, and improve the sound of the amp and speakers as well (decreased power amp distortion produced, less excursion of the Maggie Mylar diaphragms). Removing the bottom octave (20-40 Hz) cuts the amplifier power required in half!

One amp to consider is the no-longer-in production Music Reference RM-200 MK.2 (review by Michael Fremer and John Atkinson available for reading on the Stereophile website), available used for around $2500 (one just sold at that price yesterday on USAM). The RM-200 was designed specifically to work well with low impedance loudspeakers, and puts out 125 watts into 4 and 8 ohm loads (the amp also includes 2 ohm and 1 ohm taps!). It uses only a single pair of KT88 (or 6550) tubes to produce those 125 watts, yet the tubes last around 10,000 hours.

Then add a pair of subwoofers to reproduce the low bass. Planar devotees have employed this tactic for decades, all the way back to the QUAD ESL of the 1950’s. I’ll post below a video Danny Richie of GR Research made on the subject of high pass filtering loudspeakers and adding subs:

https://youtu.be/65eFr2rKy3M?si=rftln4L2ryHM_yvf

Have you ever thought about getting a hybrid amplifier?  I’m currently using PS Audio BHk preamp and 300 mono blocks.  They have a tube input section and the amps have a Mosfet output section. Plenty of power and warmth.