OPERATING / SERVICE MANUAL
FDA 18
QUICK START
You’re in a hurry, so you better read this quick, so you can get started right away.
The input may be mic or line level. Choose by pressing the pushbutton located near the
MASTER control. A balanced input uses “+” as hot, “–” as return and GND as shield ground. An
unbalanced input should connect to “+” and GND. Leave “–” unconnected.
The outputs are “+” and “–”. Normally GND is not used on the sending end. Ground the
shield only at the receiving end.
Signal for the outputs is sourced either before or after the MASTER level control. The switches
which determine this are located within the confines of the unit’s covers. All FDA 18s are
shipped from the factory with the switches in the POST position.
Once the input and outputs are satisfactorily connected, set the input gain as high as possible
without causing the overload (OL) indicator to illuminate steadily with very high input levels.
NEVER CONNECT ANYTHING EXCEPT AN APPROVED RANE POWER SUPPLY TO
THE RED THING THAT LOOKS LIKE A TELEPHONE JACK ON THE REAR OF THE FDA
18. This is an AC input and requires special attention if you do not have a power supply EX-
ACTLY like the one that was originally packed with your unit. See the full explanation of the
power supply requirements elsewhere in this manual.
SYSTEM CONNECTION
When connecting the FDA 18 to other components in your system for the first time, LEAVE
THE POWER SUPPLY FOR LAST. This gives you a chance to make mistakes and correct them
without damage to your fragile speakers, ears and nerves.
INPUTS. The input on the FDA 18 is fully differentially balanced, i.e., it is a true instrumenta-
tion amplifier. It may also be used in an unbalanced configuration. Use only shielded cable for
your input. This wire should always be two-conductor plus shield, even for unbalanced operation.
Balanced inputs should be connected to the “+” pin and “–” pin for signal hot and return. The
shield should be tied to GND. A neutral “pin 1” ground is not necessary (except when using phan-
tom power). For unbalanced use, connect the hot side of the input cable to “+” and the signal re-
turn to GND. It is never necessary on any Rane Flex module to ground the pin 3 input in the
unbalanced mode; however, it won’t hurt anything either. If the input is coming from another
piece of equipment (as opposed to a mic), connect the shield only at the receiving end to help pre-
vent ground induced hum. If a microphone is the source, connect the shield to the case of the mic
as well as pin 1, and to the ground terminal on the unit. This is mandatory when using phantom
power.
OUTPUTS. The FDA 18’s outputs are fully balanced using a cross-coupled type of output line
driver stage. Use two conductor shielded cable for interconnecting to the next piece of equip-
ment. Normally, grounding the shield only at the receiving unit gives the best shielding, and the
most hum-free performance.
The cross-coupled output stage is capable of driving lines as long as 1000 without problems.
Longer lines (in excess of a mile) can be driven by directly paralleling two outputs.
