A
lot of friends ask me a circuit AUDIO MIXER, for various uses. I will
begin with a circuit which you can it manufacture, as you want. This you
can place in the MODULES of inputs any circuit you want, depending on
the use that you intend the MIXER, the same is also for the number of
input channels, that you will manufacture. Below I will give enough
circuits with various levels of quality and complexity. All the circuits
that propose and are simple also they maintain, a very good level of
quality. For those who they are interested they can make few patience.
Shortly I will give project, professional level console of mix signals
of sound.
In
the Fig. 1 exist the main circuit of MIXER-6Ch. It is constituted by 6
input channels. The channels from CH 1-4 are monophonic channels. The
circuit that you will select for this place, can be in input connection,
BALANCE or UNBALANCE [ Symmetrical or asymmetrical ], have POWER
PHANTOM, for Electret
microphones, use various types plugs of input. The channels CH 5-6, are
intended for stereo use. The number of input channels they can increase
itself as long you want, making choice between mono and stereo of
circuits. More details for the input circuits I will give separately for
each circuit. The output of each channel drive the RV1-6, that
potesometer regulation level of sound. With RV7-12 we create conditions
of balance between two channels [ panoramic potesometer [ BALANCE ]].
All the signals from the input channels in this point are added by two
adders [ IC1a-b ], for each channel Here exist two trimmer TR1-2 that
adjust the gain of each IC, adapting the level of signal of output, in
the level that we want. They can be suppressed if you do not need such
something. The next stage is a EQUALIZER [ Fig. 9 ], three band of
regulation. The IC3α-b, constitute the output of MIXER, they are have
gain one and they make the essential isolation of previous stages, with
the unit that we will drive. For whoever they want they use headphones,
it exist a classic circuit drive of headphones, round the IC2a-b, that
give output in the JF13. It can also exist also optical clue of audio
level, with a STEREO VUMETER. Circuit that you can select between what I
give in the category of VU Meters or that other you want. The supply of
various circuits becomes from the power supply that connect to JF12b
and gives a variety from voltages, that probably will need. .
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R1…..12=4.7Kohms |
RV1….4=47Kohms Log. [Fader] |
C19-20=220uF 25V |
R13…..24=10Kohms |
RV5-6-13=2X47Kohms Log. [Fader] |
Q1-3=BD139 |
R25-26=22Kohms |
RV7….12=10Kohms Lin. pot. Log. |
Q2-4=BD140 |
R27-30-34-39=100ohms |
TR1-2=4.7Kohms trimmer |
IC1-3=NE5532 |
R28-29-36-37=100Kohms |
C1….8=10uF 25V |
IC2=NE5532 – TL072 |
R31-42=10Kohms |
C9-11=47pF ceramic or mylar |
JF1….6=XLRFemale Plug |
R32-41=4.7Kohms |
C10-12=47uF 25V |
JF7….11= RCAFemale Plug |
R33-40=10Kohms |
C13-14=100uF 25V |
JF13=JACKFemale Plug |
R35-38=47ohms |
C15-16=2.2uF 16V [C17-22=No use] |
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All the Resistors is 1/4W 1% metal film |
C18-21=100pF ceramic or mylar |
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Modules for mono Input Channels
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A
simple choice appear in the Fig. 2, in asymmetrical [ unbalance ]
connection of input. It uses integrated circuit [ IC1 ], in inverting
and possibility of regulation gain of unit, for low levels [ microphone ]
up to high [ line ]. With switch S1 we can, if it is necessary we give
supply for the operation of Electret, condenset microphones.
In the place of IC1 we can use a variety from integrated circuit that
give below. The type of integrated circuit that we will use, depend from
the number of input channels, that we will manufacture, for this reason
I do not give also concrete type. My own choice is: IC1=NE5534 – NE5532 – LM833- TL072- TL074.
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Electronic Balance Mic-Line input Module
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In
the Fig. 3, appears one stage with much better characteristics, in
symmetric connection [ balance ], with continuous regulation of stage
from the potesometer 22KΩ. This give the possibility for regulation of
sensitivity, from low input levels until high. And in this circuit I do
not give concrete type for the IC1-3. The choice can become from the
below list, according to the characteristics the each IC and
proportionally use for which him we intend. My own choices are:
IC1-2=NE5532 – LM833, IC3=NE5534 – TL071.
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Microphone transistors preamplifiers
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In
the Fig. 4-5, exist two choices for preamplifiers of microphone that
use transistor, in asymmetrical [ unbalance ] of input connection. For
the supply of this stages, exist two choices. The first choice, are with
diode zener, the other choice, use voltages that give the regulators,
from main power supply..
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- Mic/Line Balance input Professional
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Modules for Stereo Input Channels
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For
the modules of inputs stereo, exist two choices, that appear in the
Fig. 6-7. The first choice in Fig. 6, it is in symmetric input
connection [ balance ], while in the Fig. 7, exist one of simple
asymmetrical input connection [ unbalance ]. The gain of also two units
is one. This gain can increase itself, if this need, if we increase the
price of resistors that is parallel with the capacitors 33pF. Should
these resistors be equal between them.
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Stereo Phono Preamplifier [RIAA Filter]
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In
the Fig. 8, exist a classic preamplifier PHONO of correction RIAA, for
those who they insist they use disks of vinyl. For good precision in the
reproduction of sound, should the materials that find in the negative
feedback and correct RIAA, to be good quality, as resistors of 1% metal
film, the capacitors polypropylene and Mylar. The capacitor C8,
adaptation in the input, can change with such price, so that it suits
with the characteristics of cartridge that we will use. In the place of
IC1 we can use also the LM833 or other completed low noise integrated
circuit.
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In
the Fig. 9, exist a simple and classic circuit EQUALIZER, three band,
low, mid and high frequencies, with gain of regulation [ ±18 dB/oct ].
All potesometer they are doubly linear and good quality.
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Power Supply for 6 Ch MIXER
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The
Power supply in fig. 10, he is very simple in his designing. There are
four regulators that for us provide a variety from voltages, that
probably we will need. The basic voltage are ±
15V. The voltage of + 12V is intended basically for the circuit of
VUMETER. If we do not use electronic VUMETER, we can him suppress. The
himself is also in effect for the voltage of + 5V, (is intended for the
input circuits, with transistor [ Fig. 4-5 ], if we do not use the zener
diodes). For until 6 input channels the regulators, it does not need
they are placed in heatsinks . For more channels good it will be they
are placed on heatsinks. Is good transformer T1, it is placed far by the
remainder circuits.
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In
the Fig. 11, appear various choices of connection for various types of
plugs, that you can use in all the input circuits. Attention should be
given in the connections, so that are not created bronchuses, so that we
have hum. The clue [ + HOT ] correspond in signals inside phase, while
clue [ - GOLD ] in out phase signals. All the components should be good
quality. .
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Typical characteristics for IC’s, that I propose
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The MIXER-6Ch, can be manufactured in a box, which
the above surface will have a certain bent. In the place RV1-6, can be
used potesometer Fader. So if you cannot accomplish with this
manufacture, you can use simply rotatively potesometer in all the
places.
* If you use NE5534, it should you place capacitor 22pF between pin 5 and 8 .
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Pre Fader Listen [PFL] stage for Audio Mixer
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Monitor Sel. From Mixer Input Channel To Headphone
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Many
friends asked if its possible in the MIXER exist also a circuit
monitor, so that is possible the pre-listen channels without they are
open pot. Fader or they can hear that it exist in the each input
channel, parallel with the sound that goes to the main output, without
exist his effect of one in the other. This work him they make the
circuits that I give. In the Fig.13, exist a circuit that this listen
becomes from independent switches, with possibility of listen all
channels, we want. Parallel, exist also diodes LED D1-6, that shows more
channel is open. Then exist a classic summing amplifier and a
potesometer that regulates level to headphone amplifier. This signal is
charged with the mainly signal, but only in a headphone amplifier. If
the circuit became complexer, we could cut the signal from exit L-R,
when we pressed some switch. In the Fig.14, exist a circuit that make
the same work, but is simpler. Instead of switches, exists a double
rotary switch, that select only a input channel each time. In the place
of IC1, it can enter somebody from opamp. that propose, choice of that
will be proportional units that will be used.
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