The A-Designs EM-Silver is a single channel microphone preamp for 500 series style rack casings. A-Designs has a whole line of different colored (both visually and sounding) 500 series mic preamps. I've used a couple of them in this line, as we have a few different types in the B room at the studio where I work. The EM-Silver is one of my favorite of the bunch, but all of them sound great in their own way. The pre has built in phantom power, a -20 db pad, and a phase reverse button. The only connection of it's own that the pre has is a 1/4" input for using it on the DI, otherwise you use the connections on your 500 series casing for it. It isn't usable or rackable outside of a 500 series Lunchbox casing...
If you understand how to use a microphone preamp and the features involved with one, the A-Designs EM-Silver is going to be a breeze to use. It has a gain knob to go along with the aforementioned standard features that you'll normally find on a mic preamp, and that's really it. You won't find anything out of the ordinary here, which is a good thing as it makes it quite easy to use.
The A-Designs EM-Silver definitely has it's own sound, especially when compared with a few of the other preamps in this series. They recommend this one for use with ribbon microphones, so of course that is what we primarily use it for. I've tried it out using a Royer 121 on a guitar cabinet, and the results were nothing less than fantastic. It's definitely a bit gritter than your average mic preamp, but I like this a lot when used in the right situation. The preamp has a good amount of headphone available to it, so I'd be curious to try it out with an older ribbon microphone that might not have as high an output as the 121. I've also used the EM-Silver for a bass guitar cabinet microphone, which also sounded awesome, so this mic pre is definitely not only limited to use with ribbon mics...
A-Designs is an innovative company, as I love the idea of the 500 series line or mic preamps that they've put out. The EM-Silver is one in this line, and is one which has all it's own sound. Before choosing one in this series, I'd recommend hearing each if possible to see what might work best for you, as each really is it's own animal. All are about the same price, so it should just be a matter of preference. Heck, if you can it would be awesome to have a full rack of each one these 500 series modules. However, if you can only do one, the EM-Silver is a great place to start!