acidjack, any device that runs on 9 VDC and delivers 48 VDC at its outputs must be using a DC converter internally. Those critters contain oscillators that generate AC, usually at some fundamental frequency that's reasonably far above the audible range. Most often these days, that oscillator then feeds a "ladder" of diodes and capacitors which rectify and smooth the AC at a higher peak voltage than the input--so in effect, you get a kind of "DC voltage multiplier" effect. But oscillators are never perfectly efficient--there are always some energy losses in their operation. As a result, running this supply with no microphones connected will definitely run down your battery. The only question is how fast.
According to DPA's Web site, your microphones draw 2.6 mA apiece. But how long a battery supply will last with a given load is nearly impossible to calculate directly. So to get a reliable answer to your question about the 3-hour concert, I'd suggest that you invest the cost of a 9-Volt battery of the type you're thinking of using. Plug both your mikes into your supply at home, but before you put the battery in, loosen the shell of the XLR plug from one of your mikes so that you can measure the DC voltage between (say) pin 2 and pin 1. (You could also measure between pin 3 and pin 1, but not between pin 2 and pin 3--they should always be at the same DC voltage.)
Put the battery in and observe the voltage when the battery is fresh (with a 2.6 mA current draw, you should see ca. 39 Volts). Then you might wait and see how long it takes for the "low battery" light to come on. (With both of my PS-2s it comes on well before it's necessary to change the battery. I guess it's better that way than the opposite.) You might check the voltage again then, leaving the mikes connected--it probably won't be much lower than it was initially. Then recheck the voltage periodically for a while, and see whether you get to anything near 3 hours with the voltage still in range, i.e. not dropping more than about 4 Volts from what it was when you started. That should tell you what you need to know.
Two notes: One is that I really did mean that the supply voltage should be around 39 VDC with a fresh battery and a microphone connected to each input, even though this is a 48-Volt supply. Phantom powering is a little funny that way; the voltage is specified with no microphone connected. As soon as a microphone is connected, current is drawn through the matched pair of supply resistors that each input channel has--and that causes a voltage drop across the resistors which is proportional to the current being drawn. In this case, Ohm's Law tells you to expect 1.3 mA (per resistor) times 6.8 kOhms (the value of each resistor) for a voltage drop of 8.8 Volts. Thus the "ca. 39 Volts" figure.
The other note: The outputs of your microphones, and of the PS-2, are balanced while the mike inputs of your M-10 are unbalanced. That's always a touchy situation, because only the manufacturer of the microphone (or someone else who knows its specific output circuitry exactly) can tell you how you should wire an adapter to unbalance the signals from that type of microphone. It's different with different manufacturers, and sometimes even with different models from the same manufacturer. Don't let anyone ever tell you that there's a standard wiring scheme for doing this, because there's not. Doing it the wrong way (even if that happens to be the right way for some other microphone) can cause all sorts of problems.
Unfortunately DPA's information PDF for this microphone doesn't say how to wire it for unbalanced operation, so I think you'll have to contact them directly and ask. I really, really don't advise taking other tapers' word for how this should be done (I can explain why I'm saying that if you want me to, but I've taken up too much space here already with this message); get the information from the horse's mouth.
--best regards
Topic: Using a Denecke PS/2 - any advice? (Read 2787 times)