What is the best premp for Atma-Sphere MA-1 3.3 amp?

^^Yes.

Of course, X350.5 is giving out 350W at 8 ohms in the frequency range where most music lives and is therefore much more powerful than MA-1. Then the question is whether I need 350W in the flat portion of the impedance/frequency curve if I don't listen at rock concert levels and my room is medium size 400 sq ft. What do you all think?

@chungjh You've put your finger on the issue. ESLs in general have their impedance curve deriving from a capacitance which is intimately involved in the electrostatic principle.

As a result the impedance curve does not reflect on the efficiency of the speaker! In a normal box speaker, the impedance bump in the lower frequency is a common example of how the speaker has a higher efficiency at the resonance of the woofer in the box- and this is seen also as an impedance peak. The higher impedance of ESLs in the bass is not caused by resonance- and so for the speaker to do 86dB at one meter in the bass region takes the same watt of power to do so as it does at 1KHz or 10KHz. Yet the impedance of the ESL is quite different at these frequencies; in the bass the Sound Labs get to 30 ohms and are much less at 1KHz and even lower at 10KHz. If the amp can double power as the load impedance is halved this also means that the amp's power is cut in half as the load impedance is doubled. This is why the MA-1 makes more power than the Pass on the Sound Lab.


Al has already gone over that bit; the one thing not mentioned was the issue of transients which gobble power mostly in the bass. This is why the MA-1 will seem across the board about the same power on the Sound Lab as a solid state amp that makes over 400 watts.


One other thing to keep in mind- while the 86dB number makes most speakers impractical in many rooms, a line source such as the Sound Lab can be corrected by adding about 6dB once you are about 10 feet back. So 92 dB is then more practical. This is exactly the same phenomena where the volume does not appear to increase as you move closer to the speaker, unlike point source speakers.

Room size is approx 16' x 26' with 10' ceilings. M-60's with Zero Autoformers (not enough power) Bricasti amplifiers as well as Merrill Audio Veritas and even tried the new Merrill Element 118's. There were other amps as well and again just could not get the SL 545's to sing.

@sksos M-60s with ZEROs simply won't have enough power to make the Sound Labs play. Just as a FWIW: amps that have an extremely low output impedance like the Element simply won't be able to play a speaker like the Sound Lab- there likely was nothing wrong with the speaker; it just wasn't being set up properly. In a room of that size you'll need some power! For more on how this works see:http://www.atma-sphere.com/Resources/Paradigms_in_Amplifier_Design.php
Sound Labs (like all ESLs) are not Voltage Paradigm devices. So amps that can double power as the load impedance is cut in half aren't going to work very well on them. Sound Lab is by no means the only speaker that is a Power Paradigm device- lots of horn a full-range single driver (example of the latter: ZU loudspeakers) are as well. SETs fall into the category as well.