VAC Auricle Mk I Amplifier User Manual
Page 6
Page 6
OBTAINING THE BEST PERFORMANCE FROM Auricle
Output Tube Bias Adjustment:
Your Auricle has been shipped with the output tube bias properly set. Nonetheless, it should
be checked when you install your amplifier and approximately once every month thereafter.
It must also be adjusted each time a tube is replaced.
Remove the small black ‘acorn’ caps from the bias adjustors, which are loctaed near each
output tube. Allow the amplifier to reach normal operating temperature (about ten minutes
of warmup should be sufficient). Mute the preamplifier. Turn the bias test switch to each
tube position in turn and observe the bias meter. Using a long handled screwdriver, rotate
the control by the appropriate tube until the needle is centered on the small white dot. Repeat
for each of the output tubes and then, because the adjustments can interact slightly, recheck
all four tubes, in the same order as before.
NOTE:
The tubes are very hot (up to 250 degrees centigrade) and can cause
severe burns. Be extremely careful not to come into contact with the tubes
when making these adjustments.
Matching Auricle To Your Loudspeakers:
Like many modern tube amplifiers, Auricle includes multiple “transformer taps” for the left-
and right-channel outputs. The rear panel includes separate binding posts for each channel’s
4, 8, and 16 ohm taps. Do NOT assume that the tap which corresponds to your speakers’
published impedance specification will yield the best sound. Due to the various standards
by which impedance can be measured, not to mention the fact that a speaker’s impedance
varies with frequency, it is impossible to assert with certainty which output tap will yield the
best sound. For this reason, VAC strongly suggests auditioning your speakers through both
taps. In general, we find that a speaker’s minimum impedance is more important than its
nominal (average) impedance when determining which tap is correct. A lack of bass
response often indicates that a lower impedance tap should be tried.
Precautions: To avoid risk of injury from hot tubes, allow unit to cool before coming into
contact with the tubes.