11
THE OUTPUT CONTROL
As mentioned in the “Front Panel Controls” section, we have found that the UnFairchild can sound really
good when pushing A LOT of level through it. By reducing the output level, you can get the benefits of pushing a
lot of level without clipping the input of whatever device comes after it. The setting we generally use for this is to
turn the input gain on the UnFairchild all the way up (don’t be shy... This thing sounds great when it’s pushing a lot
of level). Then adjust the “Threshold” control for the desired amount of compression. If the resulting output level
is clipping the input of the following device (A/D converter, EQ, etc.) then simply turn down the output level with
the “OUTPUT” control on the UNFa-1 until you have the appropriate level.
Some of you may have noticed that under very extreme compression settings the right and left sides
can sound a little different even when stereo linked. This is due to the inherent limitations of the design utilizing
Vari-Mu tubes for the gain reduction. Differences in the tolerances of the tubes can be more significant when you
get deeper into the gain reduction curve of the tubes. The original Fairchild 670 did not even offer a stereo linked
mode, maybe for this reason. The issue can be compensated for by adjusting the bias current of each collection
of 4 tubes for the left and right sides. We are using the bias current adjustment as the “GAIN TRIM” control on the
UnFairchild (bias current also is a great way to adjust the overall level of a channel). With output level control on
the UNFa-1 you can now use the “GAIN TRIM” control on the UnFairchild to match the stereo compression for ex-
treme compression settings while maintaining the left/right balance of the two channels. If you are applying very
extreme compression on a sound source, let’s say a drum mix, and you hear the left and right sides not matching
perfectly, then listen to each side individually and determine which of the two sides sounds more compressed.
Turn up the UnFairchild “GAIN TRIM” control on the side that sounds more compressed by .5dB and then turn down
the “Output” control on the UNFa-1 .5dB (1 click) to match the level. Listen again and see if the two sides are better
matched. You can repeat again if the same side is still sounding too compressed.
THE AVG MODE
The “AVG” or “Average” mode offers a different way to achieve stereo linked compression. There are now 3
ways to have both channels compressing the stereo information the same or similar.
Original Link Mode - (UnFairchild set to Link, UNFa-1 “AVG” off or in the down position). If you only use the “Link”
mode on the UnFairchild than whatever channel (Left or Right) has the loudest signal will take over and trigger
compression on both channels. This is best when you want the compression to be more sensitive to signals that
are hard panned left or right. Signals that are hard panned will compress approximately 3dB more than if they are
panned to the center (depending on your “pan law” setting).
Link + AVG Mode - (UnFairchild set to Link, UNFa-1 “AVG” on or in the up position). With this combination of
settings, the left and right signals are summed to mono before being sent to the side chain. The result is that the
UnFairchild will compress more consistently regardless of where something is panned. The benefit of this is that
hard panned signals will not excessively pull down the level of a whole mix.
IND + AVG Mode - (UnFairchild set to “IND”, UNFa-1 set to “AVG”). With this combination of settings, the identical
mono summed signal is being sent to both channels but the channels are not linked together. You can manually
set the UnFairchild for the best matching of left to right compression. The benefit of this that occasionally the tol-
erances of the tubes make it difficult to electronically link the two channels together and have them match exactly
with extreme amounts of compression. With this setting you can simply match them by ear.