Six-channel stereo mixer for active loudspeakers. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Musician

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The author proposes a simple six-channel stereo mixer using an op amp that provides signal amplification if necessary, as well as an adapter that, when installed in it with various types of connectors, will become a useful device for interfacing audio or multimedia complex devices.

Many personal computers are equipped with external active speakers that can be used for other purposes, for example, for working with electric musical instruments, microphones, in audio effects systems, audio and video surveillance, etc.

Fig. 1

On fig. 1 shows a diagram of a simple six-channel stereo mixer for an active speaker. Such a device can be used to serve up to six stereo sources or 12 mono sources.

Inputs XS1-XS6 are intended for summing signals of one channel, and connectors XS7-XS12 - for signals of another channel. Instead of two-pin connectors (all or part of it), you can install three-pin connectors that are suitable for switching and connecting stereo audio equipment.

The signals from the XS1-XS6 connectors sum up the DA1.1 op-amp, and the signals from the XS7-XS12 - the DA1.2 op-amp. The outputs of two channels (stereo) are connected to connectors XS13 and XS14.

When the contacts of the SA1 switch are closed, the signals from all 12 connectors XS1-XS12 are added to XS14. The output of wires from the SA1 contacts to external circuits (conventionally marked "A" and "B") can be used to potentially control another device.

Op-amps with OOS circuits provide transmission of line-level signals without attenuation (through connectors XS4-XS6 and XS10-XS12) or with a gain of more than 60 (1 MOhm / 15 kOhm = 67), if the resistance of the signal source connected to connectors XS4-XS6 and XS10- XS12, less than 1 kΩ. The input impedance of the mixer at the input with gain is 15 kOhm. These inputs can be used to connect microphones or other low level sources.

The line level inputs are 1 MΩ impedance and should be used to connect the outputs of a sound card, electric guitar, EDA recorder, or other high level sources.

As adders, you can use operational amplifiers of the NE5532A, TL072 series, which are distinguished by low input current and low noise, or similar. The first of these microcircuits may be preferable when the load resistance is in the range of 600 Ohm ... 2 kOhm. The mixer is operable in the full range of the supply voltage of the applied op amps

Rice. 2 (click to enlarge)

On fig. 2 shows the power supply circuit for the described mixer. The use of voltage stabilizers in the block helps to reduce the supply voltage ripples, which are unacceptable for low-signal amplifiers. The mains transformer on the secondary winding creates an alternating voltage of 2x18 ... 20 V at an average current of 0,1 A, sufficient after rectification for the operation of integral stabilizers for a voltage of +/-15 V. It is permissible to choose stabilizer microcircuits from a wide range for a voltage of 5.15 V, providing load current up to 100 mA.

Fig. 3

On fig. 3 shows a diagram of an adapter with connectors for stereo inputs. Using such an adapter, stereo signals can be routed to separate cables (connectors), and vice versa (each triple of connectors can be used "reversely"). By the way, it is not at all necessary to combine all the "triples" of connected connectors together with a common wire, this will exclude loops along the circuits of the common wire, which can create an alternating current background.

Instead of part of the mini-jack input connectors (TS, TRS to 3,5 mm) in the mixer and adapter, you can install five-pin connectors ONTS-VG (DIN-5/180^о) or others.

Mixer and power supply do not require adjustment; they will work if the parts are in good condition and there are no errors in the installation. The design of this device may vary depending on the capabilities, location of the device and ease of use.

Author: P. Petrov

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