Peavey 900 - Page 2

INPUT CIRCUITRY - In order for a mixer to be
compatible in most applications, it must have the
capability to control the sensitivity of the input circuitry
of each channel. This requires an ATTENUATOR (1),
sometimes called a pad. Some mics and signal sources
can be at such a level as to overdrive or clip the input
circuitry of a mixer. An input attenuator allows the
operator to reduce the input gain when input clipping
occurs. Some manufacturers put attenuators in their
snake or stage box to be able to control the sensitivity of
the mic or signal source. This is not the best approach if
you are sending your signals through cable runs of any
length. The more signal being carried by the mic cable
the less susceptible is the signal to picking up hum or
noise which allows for an improved signal-to-noise
ratio. Many times it would be impossible to make an ad¬
justment on one of the attenuators if necessary during
the performance You shouldn’t have to run up to the
stage and pick up the drummer's leg so you can adjust
a mic input!
In use, ■ the operator must adjust the input
attenuator in such a manner that input clipping is avoid¬
ed. This can easily be done by setting up the channel
v/ith the highest expected input signal level and ad¬
justing the input attenuator so that no clipping or distor¬
tion is heard from the speaker system. Alter the mixer
has been used several limes, the operator will have a
very good idea of the signal levels encountered and will
be able to set up the attenuators accordingly. The
different types of microphones will have different output
levels and different performers will get widely varying
levels from mics depending on the strength of their
voices and/or their basic "mic techniques".
The input attenuator should be operated in the
position yeilding the least attenuation required to avoid
clipping. Operation in this mode allows maximum gain
to be utilized in the input preamp where it is most ef¬
ficiently obtained. Excessive input padding sometimes
makes necessary higher settings of the channel gain
controls and/or master control thus yeilding a less than
optimum signal-to-noise ratio for any given situation.
It is important to realize that not all "breakup” is
caused by the mic signal overloading the input stage of
the mixer. If the performer’s mic technique includes
very close and/or very loud situations, the internal
elements of the mic can “bottom out" or distort just as a
loudspeaker can when it is overdriven. Quite a few of
the mics now used by performers lack the dynamic
range required to adequately handle the tremendous
sound pressure levels encountered in a very loud rock
and roll concert situation. It is vital for the professional
soundman and the musicians to be aware ol the
limitations of the various links in the audio system in
order to correctly diagnose and solve the various
problems encountered in a sound reinforcement situa¬
tion.
Overall, the input attenuator is the first control in
the circuit and must be set up properly in order for the
remaining circuits to function properly. "Common
sense" and experience operating the 900 Mixer on
several jobs will allow the operator to achieve superb
results in virtually any nixing situation. Our variable in¬
put attenuator allows for much more flexibility than
some other manufacturer's mixers that only have
switchable fixed attenuation of maybe 10 to 20 dB.
where sometimes 10 dB may not be enough and 20 dB
may be too much attenuation. The 900 Mixer’s input
attenuator is continuously variable from 0 dB to -40 dB.
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INPUT ATTN
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15 +
LOW
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