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Vocal Zapper 9
Now comes the big test. Switch S1 to the Zap mode, and the lead vocal should
drop out as if by magic. If it doesn't, adjust trimpot R12 for the maximum
amount of cancellation (this should occur somewhere near the midpoint of
rotation). Once set, this trimpot need not be changed as you play different
records unless you are altering it for a specific effect.
Now that the lead vocal has been eliminated, it's time to try out the microphone
preamp. Plug a microphone into the J5 with trimpot R11 set full counter-
clockwise and the gain on your stereo tuned all the way down. TO PREVENT
FEEDBACK THE USE OF HEADPHONES IS RECOMMENDED.
Adjust trimpot R11 for the proper blend between microphone and program
material. Note that most people tend to set the mic gain too high at first so that
they can hear themselves well; however, excessively high mic gain settings can
cause distortion. If you experience such distortion, back off on R11 a bit. Now
with the unit in the Zapped mode, you can sing (or howl) along with some of the
world's best backup musicians playing for you. Please note that the Zapper will
not work with mono program material, but stereo tapes, records, or FM with
good separation will work in almost all cases.
PRINCIPLES OF VOCAL CANCELLATION
With most stereo records, certain instruments are traditionally placed in the
center of a stereo mix, such as vocals, bass, and bass drum. Other instru-
ments, such as lead guitar, keyboards, vocal harmonies, and the like are mixed
more towards the right or left side of the stereo spread.
The Vocal Zapper removes the
lead vocal according to the process
shown in the figure. The right and
left channels of a conventional
stereo recording are summed
together in a differential amp (IC1).
As a result, all center channel
material, including the lead vocal,
is cancelled at IC1's output. The
remaining instruments that are
mixed more to the right and left
sides are relatively unaffected.
In order to prevent complete cancellation of the bass and bass drum, C3 only
allows frequencies above approximately 160 Hz to be cancelled. Frequencies
below 160 Hz are not mixed differentially, meaning that bass information
present in the right channel will appear at IC1's output. If you prefer complete
suppression of the center of the stereo field and do not mind losing some
bass, you can change the value of C3. Values between C3's current value of .01
mfd and .22 mfd. will cause greater rejection as the value is increased.
MIC
INPUT
MONO
OUTPUT
STEREO
INPUT
HIGH PASS
FILTER CAP
DIFFERENTIAL
AMP
PREAMP
IC1:A
IC1:B
R
L
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