1. INTRODUCTION
Congratulations on your purchase of the mythological UnFairchild! It does actually exist, a faithful, mod-
ern revitalization of the original Fairchild! The Undertone Audio team worked passionately to preserve
the character of the Fairchild sound while improving the reliability, functionality and affordability of this
legendary circuit. From our sound lab to yours, we sincerely hope you will find the results as useful and
satisfying as we have.
What’s different about the UnFairchild 670M II from an original Fairchild?
We are using Cinemag recreations of the original transformers used in the audio path. They are
extremely close to the originals with only small adjustments made to accommodate a more desirable gain
structure. The side chain circuit has been simplified to improve reliability and affordability and because
the original design was totally insane. It’s still a tube circuit..it still preserves the important sonic character-
istics of the original...the only difference is that it’s not insane.
The original Fairchild runs at a very high plate voltage. So high, in fact, that the original Fairchild
manual recommends that you should change the tubes every 6 months. We lowered the plate voltage
going to the 6386 tubes to help extend their life and reliability. 6386 tubes can cost anywhere from $120
-$500 each and the unit uses 8 of them! Best case you’re looking at $1,000 every 6 months to be sure an
original Fairchild is running up to spec. This is one of the reasons so many of them sound so different from
one another...and why some sound so
bad.
With the lower plate voltage and a good set of tubes, the Un-
Fairchild will run reliably for years.
MORE CONTROL:
We’ve added a wider range of controls. As cool as the original Fairchild is to own, it’s
cooler to have that sound with modern flexibility. The UnFairchild offers the legacy of the Fairchild; with
much more of what one would expect from a compressor built in 2018.
In addition to the original time constant presets there are:
• Independent control over the Attack and Release
• User control over the DC Offset (functions similar to a ratio control)
• Access to processing or EQing the side chain signal
• Fine-trim adjustments for precise matching of the L/R balance
• True stereo linking
• Multiple M/S processing modes
• Options for feed-forward compression
• Calibration for meter level acuracy and channel compression matching
• True bypass
• Output metering
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