manitouman, you asked:
> On the M-Audio site it states: "Professional balanced ¼” TRS inputs capable of mic or line-level signals." So does this mean the signal from the preamp, in my case the 9100, needs to be a balanced signal? One gain knob controlling both mics is NOT a balanced signal? Someone enlighten me please.
This use of the word "balanced" doesn't refer to the relative levels between the two channels, such as the "balance control" on a stereo amplifier or receiver would affect. Instead, it refers to the preferred way of sending signals down a cable in professional audio, which differs from the way used in consumer audio.
In consumer audio, cables are shielded, the shields are connected to the chassis of the equipment that they're plugged into on both ends, and each channel has one signal-bearing lead wrapped within the shield. In balanced connections there are two independent signal-bearing leads within the shield for each channel. Neither signal lead is connected to the shield at either end of the connection.
Also--this may seem technical, but it's essential--those two signal-bearing wires are at the same impedance (relative to ground) as each other. That's what creates the "balance." Because of the identical impedance, Ohm's Law tells us that as the signal voltage rises and falls, the current flowing in the two conductors will always be identical to each other at any given moment, with equal and opposite signal voltages.
That's the key, since a balanced input responds ONLY to the difference in voltage between those two leads--ignoring the voltage between either lead and ground. Any interference that the cable picks up should affect the voltage in both signal leads equally, leaving their voltage relationship intact. In this way a balanced input essentially ignores interference, and that's why balanced connections are the norm in professional audio.
A typical unbalanced input connector is an RCA socket--a coaxial "pin plug" such as you'd find at the CD inputs of a hi-fi preamp or receiver. It has an outer contact (shield/ground) and an inner contact which connects with the pin of the plug. A typical balanced input connector is an XLR-3F, which has shield/ground on pin 1 and the two signal leads on pins 2 and 3. The MicroTrack's "stereo phone" sockets are an alternative to XLR sockets, with the shield/ground on the sleeve of the connector and the tip and ring being the two signal connections.
Any balanced input can accept unbalanced signals, but not all ways of hooking up such an arrangement are created equal. The ideal way, if you want best noise immunity, is to create a balanced signal at the output of the signal source; then use balanced cable and a balanced plug. There are other ways to connect unbalanced sources to balanced inputs, but they don't get you the noise immunity of a balanced connection.
--best regards
