Sound Devices MM-1 Single-Channel Portable Microphone Preamp

According to the Sound Devices Manual, to give you a ballpark figure, with Duracell AA MN 1500 Alkaline batteries with a condenser microphone (48V) and 75-ohm headphones at high levels, you can expect about 8 hrs. of run time. It's always good to do your own testing.

Yes, the Sound Devices MM-1 Single-Channel Portable Microphone Preamp comes with a metal belt clip.

You indeed could either use the MM1 preamp to feed a line level input in the MixPre-3 II or you could use the MixPre-3 II's preamps alone. Both preamps are fantastic and transparent, so it rather comes down to if you prefer the nuances of one over the other. In terms of need, the MixPre-3 II doesn't require any external preamps to function as it itself can very well amplify source content.

Yes, you need to make sure you have the appropriate phantom power setting; 48volt is the most common, and make sure your Alexa is set to line level input. All you need is 2AA batteries, a microphone, and two XLR cables. One to connect the mic to the MM1, and another to go out of the MM1 to the Alexa. Recommend energizer ultimate lithium batteries. They'll last days.

There are a couple of power supplies you can use:Sound Devices XL-WP3 Universal Power Supply, or for mobile power Sound Devices XLNPH NP Type Battery Cup for Field Mixers with a Switronix NP-50 NiMH NP-1 Style Battery - 50Wh, 13.2-Volt

Looks like you'll need to purchase a XLR F to 3.5mm (mono) male cable. The output of the SD MM-1 is Line level. So, the cable will need to be the type that can attenuate line level down to Mic level for the 70D to receive.

This is a mono device, but you can monitor using stereo headphones

Hi - I use this preamp with a Tascam DR-60D Mark II recorder, so I'm guessing your DR-40 works similarly. The SoundDevices preamp sends out a line signal -- not a microphone signal -- so you would set the audio recorder input to line. (Page 48 of your manual has instructions on this.) You will not need to use gain on the recorder (and, in fact, I'm pretty sure that the recorder will not offer gain for a line signal). In my work with this preamp, I've found that the preamp gain dial on the preamp is the main setting to focus on. (If you're monitoring audio through the recorder, then the mon gain and phones dials on the preamp are irrelevant.) Depending on the type of mic you're connecting to the preamp, a preamp gain setting of 36-50 dB should work well, with an input level on the recorder of about 50%. Hope this helps!