I had to look up the AM-10 spec sheet to refresh my memory...
The gain is stated as 45 dB *fixed* and the maximum output (when strapped for "high power") is + 24 dBm. Ignoring the slight tweaks possible depending upon input impedance strapping, that means that a mic level signal input of approx. -21 dBu will cause the preamp to clip.
For a close mic'ed amp, or whatever, you will need to install a pad AT THE INPUT to the mic transformer if you don't want square waves at the output of the preamp.
Be SURE the pad properly "reflects back" a load of 1000 to 2000 Ohms to the mic while presenting 200-Ohms-ish into the primary of the input transformer.
As for levels...
Think of it this way. Assume a REALLY hot signal from a condensor mic at 0 dBu (loud kick drum). The preamp adds 45 dB of gain. Thus, the output would need to be +45 dBu. But, max output level from the AM-10 is +24 dBu, so you're overdriving it by 21 dB and making some nifty clipped square waves.
But, in these times, horribly overdriven signals are "the really cool sounds" vs. Ye Olde Days when only Marshall guitar amps were required to create similar sounds. It seems that the entire recording chain needs to be spitting out square waves these days....sigh. Looking at the waveform on a scope, or in a DAW, it's like a line of toothpaste dropped onto the bathroom counter.
SO, "it all depends". If you prefer the sound of seriously clipped signal waveforms, just let 'er rip. If you don't want serious distortion from a high-level mic source, pad between the mic and preamp input. This is audio-level-matching-101! <g>
BTW, adding a pad AFTER the preamp is only useful if the recording device requires a lower input signal than +24...unless you need to clip the recorder!
Bri