Right now I have Mola Mola Kaluga mono amps which will deliver more power than I could possible need.@willgolf You might want to consider that the characteristics of an amplifier like the Mola Mola may not be right for many horn designs. The reason is that when you have the efficiency of a horn, you don’t need a lot of amplifier power, so its possible to run low power tube amps (like SETs) that often don’t run any feedback. Horn speaker designers know this and expect such amps to be used with their speakers.
The way such an amplifier behaves on a load is different from how an amplifier using a lot of feedback (and thus having a really low output impedance) acts! An amp with a lot of feedback (like the Mola Mola) typically behaves as a voltage source, meaning its voltage output is invariant with load, which also means (if solid state) that its output power doubles as the load is halved.
Tube amps with no feedback tend to behave as power sources, meaning they try to make constant power with respect to load rather than constant voltage. You can read more about this at this link:
http://www.atma-sphere.com/Resources/Paradigms_in_Amplifier_Design.php
Now most horn designers are expecting the user to use a lower powered tube amplifier. Although the Mola Mola is a good amp, because of its near-zero output impedance on many horn systems the crossover won’t work right; as an example may cross the woofer over at a different frequency than intended. The reason for this is as I explained- many of these speakers are designed for amps that are Power Paradigm devices (having an output impedance that might be several Ohms) rather than Voltage Paradigm. Any time you attempt to mix the two technologies you can expect a tonal aberration that says nothing about the quality of the equipment involved, despite the fact that both can be quite neutral if used correctly.
BTW in case its not clear, loop feedback typically used in most solid state and class D amps introduces higher ordered harmonic distortions of its own while suppressing the distortion of the amp otherwise. Because these are higher ordered harmonics, they are extremely audible as brightness and harshness (a coloration) since the ear uses these harmonics to sense sound pressure- and on that account has to be extremely sensitive in this way. This fact is a bit inconvenient, as it often means that amps with really low distortion figures might not sound as good as amps with considerably ’worse’ numbers! If the audio industry weighted the various harmonics we would have a better understanding of this fact, but they don’t so while the 2nd harmonic is recognized as less harmful than the 7th or 13th, they don’t break those numbers down to anything meaningful on the spec sheets. Horns can exacerbate issues like this, so you have to be careful.
Put more simply, the equipment matching becomes more critical when dealing with horn systems so you will want to audition your amps with the speakers you’re auditioning as well to see if you are really getting what you expect!