The AD-20 supplies no phantom voltage. I am aware the AT-822 is battery only, in fact, that is why I chose it.
Your last paragraph is interesting. You are saying I should make a cable that connects pins 1 and 3 together and uses 2 for ground? I'm afraid I don't quite understand. Could you elaborate? I'm still a little fuzzy on the concept of balanced VS unbalanced.
Not a problem..
You have an ad-20 that has balanced inputs. If you are using them. You must "unbalance" the input by connecting pin 1=ground to pin 3= Signal negative to each other.. This unbalances the input of the AD-20 and allows you to use your unbalanced microphone with this preamp. If you do not connect pin 3 to anything its floating and it can pick up stray RF signals and inject them into your recording because pin3 must be terminated by a microphone or by grounding it out. If you were plugging in a balanced microphone to this input there would be no modifications necessary.
Balanced vs Unbalanced..
Unbalanced signals are very common for electret microphones. Like the ones you have. The issue with running unbalanced line for a microphone is your are really limited to about 10 feet max before you might run into problems.
With an unbalanced microphone you only have two wires..
A Shield wire this is to prevent stray RF signals from getting into the center wire or Signal wire.
The signal wire carries the signal to the destination with the aid of the ground or shield wire.
In a balanced system you have three wires..
A Shield wire - for ground and RF rejection
A Signal positive wire. This is the in phase representation of the signal
A Signal negative wire. This is the out of phase representation of the signal
When you combine the out of phase with the in phase you get whats called phase cancellation. So what this system does is cancel out interference that is inducted into the audio chain. The output then becomes clean and free of most inducted noises. The main advantage with balanced over unbalanced is better common mode rejection of inducted signals or just "less noise" there are limits to how fare you can run a balanced cable before it needs a buffer amp but we are talking distances of more then 1000 feet. With unbalanced you have less rejection of noise so the longer your unbalanced cable run is the more likely inducted noise will occur.
Here is a simple picture I stole from a web site that illustrates what I just said.
Now because the input impedance is 200 ohms on your mic and your preamp is designed for anything from 150 to 2k if its built properly you can simply just unbalance the preamps input.
If however you were connecting a high impedance microphone to a low impedance mic preamp you would need one of two things. An impedance converter like the ones found for the AT-853 microphones... Or a Transformer that has a Hi impedance primary with a low impedance secondary.. This allows the proper impedance matching of a microphone that is high impedance to a mic preamp that is low impedance.