Five-channel mixer. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Five-channel mixer. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Musician

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A multi-channel mixer makes it possible to quickly adjust the level of signals coming from microphones or other sources, in order to then apply the total signal to the UMZCH. The proposed design provides timbre correction for low and high frequencies. For the design of the design, the case from the old calculator "Electronics BZ-02" was successfully used.

The mixer is designed to sum and adjust the levels, audio signals from five electrodynamic microphones or other sources of audio signals with a low level. From the output of the mixer, the signal can be fed to the input of a power amplifier or to a recording device. The mixer has a separate gain control for each of the five inputs, as well as a general gain and tone control for low and high frequencies.

As can be seen from the mixer diagram (Fig. 1), the audio signals through the input connectors are fed to the volume controls of each channel (to all five or several of them) and then through the summing resistors R6 - R10 to the inverting input of the op-amp DA1. Its non-inverting input is connected to ground (the midpoint of the stabilizer) through a resistor to reduce the offset voltage at the output of the op-amp. This op-amp provides a voltage gain of about 200 and is the basis of an active tone control for low and high frequencies within ±19 dB. Resistor R16 is for general gain control (volume). Op-amp DA2 - buffer repeater, matching amplifier with mixer load. The output voltage of the mixer at maximum gain is at least 1 V.

(click to enlarge)

When working from electret microphones that do not have a built-in power source, it can be obtained from the mixer by stabilizing the voltage at a level of 1,5 ... 3 V with a zener diode or LED, which can also be used to indicate the operation of the mixer. For this purpose, you can use LEDs, for example, AL307BM or AL336B, by connecting them to a constant voltage source through a resistor that limits the current of the LEDs within 5 ... 10 mA.

Since the author used the case from the old calculator "Electronics BZ-2" as the basis for the design of the mixer (its sketch is shown in Fig. 02), the rectifier, switch, fuse and power cord from the mains 220 V, 50 Hz were also borrowed from it. However, the mixer power supply can be any that provides a stabilized voltage of ±10...13 V at a current consumption of up to 50 mA.

Five-channel mixer

The mixer can also be placed in a homemade metal or plastic case. All elements of the device, except for adjusting resistors, are located on a printed circuit or breadboard mounted inside the case on racks. The connections of the board with other elements are made with a mounting wire. Housings of adjusting resistors must be connected to the common wire of the device. Input and output sockets can be of any type - "tulip" (RCA), ONTS - VG, ONTS - VN, etc.

In the tone controls, adjusting resistors SPZ - 4aM or any other with an adjusting characteristic of type B (or, in extreme cases, A) are used. Sliding resistors SPZ-23a or SP3 - 236 with a linear characteristic (A) were used as level controllers. The nominal resistance of the regulators R1 - R5 is not critical and can be increased up to 33 kOhm. The remaining resistors are C2 - 33 or similar. Capacitor C2 - oxide non-polar K50 - 6 or its analogue, made of two polar, connected in anti-series, C11 - C13 - oxide K50 - 35. Isolating capacitors C4 - C8 - film K73 - 9, K73 - 17, the rest are ceramic.

Chips DA1 and DA2 can be (and expediently) replaced by any modern general-purpose op amps by changing the correction circuits in accordance with the typical op amps used.

Author: L. Kompanenko, Moscow

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