5. CALIBRATION PROCEDURES
BEFORE YOU CALIBRATE: As the UnFairchild warms up, the calibration will typically fall into place. This can take any-
where from 10 to 30 minutes.
BALANCING BY EAR
BALANCING WITH THE METER
Balancing is important for the overall performance of the UnFairchild. When the tubes are out of
balance typically you will hear a thumping sound when the compressor is reacting to transients.
Balancing is quick and easy to do and typically is only done if you replace the 6386 tubes. Balanc-
ing is the process of equaling the voltages to the 2 sides of the 6386 push/pull circuit. Here is the
step by step process
1) Power up the UnFairchild and let it warm up for at least 10 minutes.
2) Set the BYPASS/VU Switch to BAL.
3) Set the THRESHOLD control to “0” or fully counter clockwise.
4) Adjust the BAL trim pot for the lowest possible meter reading. The meter should go all the way
down to -20 or lower.
Balancing with the meter will work for the majority of applications, but there are circumstances
in which balancing by ear may achieve better results. The balance between a set of tubes can be
different based on the amount of compression. If you are using the UnFairchild to do some very ex-
treme compression on transient sound sources; such as drums, you may hear some sonic artifacts,
such as thumping. You can solve this simply.
1) Play the sound source with the compression setting where you’re hearing the thumping.
2) While the sound source is playing, adjust the BAL trimpot until the thumping goes away.
9
CALIBRATING THE AUDIO LEVELS
The audio level calibration should be done before
you calibrate the “0” for the gain reduction me-
tering mode. Changes to the GAIN TRIM control will change the gain reduction “0” calibration. The
GAIN TRIM controls will give you around 4dB of adjustment with a 10 turn trim pot.
1) Power up the UnFairchild and let it warm up for 5-10 minutes.
2) Send a 1K sine wave audio signal at +4dB level to the input of the channel you are calibrating.
3) Set the
BYPASS/VU
control
(#7 on the upper front panel - see page 7)
to the “VU” setting.
4) Set the INPUT GAIN CONTROL
(#8 on the upper front panel - see page 7)
to 12.
