OK, it's time for a basic PA tutorial. Every PA, from small and cheap to huge and Oh-My-God, has certain components- A mic preamp with one or more mic inputs, a power amp, and one or more speakers. The preamp raises the weak mic level output to line level (like your DMP-3). The power amp raises the line level signal to something that can drive the speaker array. Most PA's also contain some EQ, which can boost or cut (attenuate) specific frequency bands to improve sound and help control feedback. They often also include basic FX (effects), such as reverb, delay, or compression.
There are several ways a PA can be configured. The system always ends with speakers, which are either active, which means the power amp is built into the speaker, or passive, which means the speakers need a power amp somewhere else to get their power. The mic inputs into a mixer, which controls the relative levels of the mic inputs. The mixer can be powered, which means it contains a power amp to drive speakers, or unpowered, which means it needs a separate power amp. A powered mixer that is designed only to drive PA speakers is called a PA head.
So, it can work in any of these ways:
1: Unpowered mixer > power amp > passive speaker
2: Powered mixer/PA Head > passive speaker
3: Unpowered mixer > active speaker
The speaker described by the previous poster is an active speaker with a built-in mic preamp, but they are not as common, and as he says, likely to be pricey. I got it- pricey is right out.
The other factors to be considered here, other than overall quality, is component matching, partacularly impedence and power matching. Impedence will be expressed in Ohms. If an amp has an 8 ohm output, it wants to be plugged into an 8 ohm speaker. PA speakers are usually 4 ohms or 8 ohms. Power matching is also critical. Plugging a 400 watt amp into a speaker designed to handle 80 watts is a prescription for trouble. The speakers will usually use a 1/4" jack, like a guitar amp, or a speakon connector, a specialized connector used almost exclusively for live speaker arrays.
So we get down to- what can work for you? Obviously you are a beginner in this area, so trying to match components without the technical knowledge is, IMHO, a bad idea. You need components that are already designed to work together. Secondly, money is a big issue. I can't make that go away, but the good news is that small PA systems are a hell of a lot cheaper than they used to be. In 1980, I paid $800 for a *used* 100 watt PA system, and that was an OK deal. Today, if I did that, anyone on this board would call me a sucker.
Next question- how much power do you really need? The good news is- not that much. We are talking about a practice PA, which would normally be used in a small room for practice, or for a solo acoustic artist to do a coffee house. That's about 80-250 watts. A serious band doing a good sized club would need 1000+ watts. Also note that watts will be expressed as program power (the home stereo people will say RMS), or as peak or peak music power. The program power is what we are talking about, that's what you can use. Peak power is what an amp puts out about 1 second before it blows up! Oddly enough, if you stay in the music scene, you'll find uses for a very small PA that you never anticipated, once you learn how to connect different pieces of equipment. The main speakers, which initially are your whole system, may be pressed into service as stage monitors later on, when you own a bigger PA. All of that said, here's a system that could meet your current needs:
http://pro-audio.musiciansfriend.com/product/Squier-4Channel-PA-System?sku=608003
I could get you down to about $200, but the system is so cheap, and the company that builds it so fly-by-night, that I can't recommend it at all. I wouldn't be doing you any favors. If a Fender product breaks, you have a fighting chance to get if fixed under warranty. Is it powerful? No. You can't afford power right now, and you need a PA. It should work fine with your SM7b. If the budget goes up, I can scale recommendations up to match it-easily. In conclusion, here's a link that will give you a more complete and more complicated explanation of the tutorial above, with a glossary:
http://www.musiciansfriend.com/document?doc_id=99523
What you need now, more than anything else, is knowledge, because people on the board who are trying to help you are assuming that you know stuff that you don't. For instance, the poster above mentioned a "desk". That is a term for a good sized mixer. When it gets big enough to impress girls with all your cool knobs and dials, we call it a "recording console". Best of luck. We have all been broke, we have all been clueless, and we all started somewhere.-Richie
