The circuit was designed for providing a microphone line with a
balance input signal to improve the quality of sound with sufficient
gain and filter.
- NE5532 – an internally compensated low noise dual operational
amplifier with features such as full power bandwidth up to 140 KHz,
input noise voltage of 8 nV, common mode rejection ratio, 9 V/us slew
rate, high DC voltage gain, 32 V peak to peak voltage swing, wide supply
voltage range from 3 V to 12 V, unity gain bandwidth at 10 MHz, and
internal frequency compensation
- TL072 – a low noise JFET input
operational amplifier with features such as common-mode input voltage
range, high slew rate, operation without latch up, compensated internal
frequency, high input impedance at the JFET
input stage, low noise, low total harmonic distortion, protected from
output short circuit, low input bias and offset currents, wide
common-mode and differential voltage ranges, and low power consumption
- BC560 – a PNP epitaxial planar Silicon
enclosed in a 24-pin dual in-line package or 3-pin TO-92 package
typically used for switching and AF amplification due to its low noise
and high voltage features
The circuit is made up of the audio from the part of input mixing
console from the microphone or from any other source made of high level.
The input can be used on the circuit itself or be multiplied to a
number of channels that can be attached to the circuit. There are
several functions that this circuit may illustrate such as reverse face,
phantom power, and signal attenuation, to avoid distortions from
signals with high level. The switches are made to function as phantom
power for S1, mic-line selector for S2, 20 dB attenuation for S3, and
phase inversion for S4.
In extreme conditions, the microphone can deliver a signal of 1 mV
up to approximately 1 V. signals of around 100 mV to 1 V can be accepted
by the line input and provides amplification. To amplify the signal as
necessary up to 1 V on peaks, a microphone preamplifier may be used to
deliver a low noise signal to the next circuitry. The phantom power
supplied to the microphone by the microphone input is around 48 V.
Using the gain control, the amount of gain can be set although there
are some consoles where there is no gain control on the line input. For
full mixing console, the gain channels are regulating the signal while
the rest of the stages will be added to the next stages. An inversion of
the signal is possible through the phase button if present. The low
frequencies below approximately 100 Hz are cut using the filter while
the signal is being attenuated usually at 20 dB.
The mic/line balance input are normally applied to the mixers which
are being used in conference rooms, rental sound systems, churches,
hotels, and schools. The direct outputs of the mixer can be utilized
with other mixers for usages which require flexible zone distribution,
room combining recording, post-production, sub-mixing, and other audio
applications.
