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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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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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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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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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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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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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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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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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Many
friends asked if it’s 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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