Universal block of regulators on the LM1040 chip. Scheme, description

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Universal block of regulators on the LM1040 chip. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Audio equipment

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The block of volume and tone controls is built on the basis of the LM1040 microcircuit, in which, by changing the constant voltage at the control inputs, electronic control of the gain in two gain channels (frequency-dependent or linear) is achieved. The low level of non-linear distortion and noise makes it possible to use this microcircuit and its close analogue (LM1036) in amateur audio equipment, as well as for upgrading industrial ones.

The regulator block with a microcircuit for a two-channel volume, balance and tone control does not have digital control and therefore can be built into any amateur stereo amplifier between the input selector and the UMZCH. The main parameters of the device (its diagram is shown in Fig. 1) exceed the level of requirements for Hi-Fi Audio equipment with fairly favorable subjective assessments of the quality of sound reproduction.

Universal regulator block on the LM1040 chip
Fig. 1

Technical specifications

Volume control range (typical), dB.......................75
Bass tone control range at a frequency of 40 Hz, dB. .+15/-15
Treble tone control range at a frequency of 16 kHz, dB .............................+15/-15
Harmonic coefficient, %, no more .................... 0,06
Noise level (typical), dB ... -80
Input resistance, kOhm, not less than ................20
Output impedance, Ohm ...................... 20
Crosstalk level between channels, dB........70
Current consumption at supply voltage 9... 16 V, mA..........................10

The levels of noise and harmonic distortion in the control channels are specified for an input signal voltage of 300 mV at a supply voltage of 12 V.

All regulators in the microcircuit are made on the basis of several analog multipliers on bipolar transistor structures. Therefore, the input selector must normalize the input voltage levels of the regulator bank by appropriate selection of resistors in the voltage dividers. It is desirable that the input signal does not exceed 400 mV rms, since at higher voltages the non-linear distortion increases significantly, especially at high audio frequencies. At a lower signal level, non-linear distortions do not exceed hundredths of a percent.

Volume control - thinly compensated, but switchable. The frequency characteristics of tone control are shown in fig. 2, and the dependence of the loudness level on the attenuation in the path is shown in Fig. 3. By changing the values of capacitors C5, C6 (HF) and C9, C11 (LF), it is possible to shift the frequency bands of regulation.

Universal regulator block on the LM1040 chip
Fig. 2

The modes of "extended stereo" (control via an electronic key on VT1) and heavily compensated volume control - KRG (switching the voltage at pin 9 using a transistor VT2) are switched on by applying a high-level voltage (+5 V); at a low level of control voltage (0...0.3 V) these modes are disabled.

Universal regulator block on the LM1040 chip
Fig. 3

As an electronic key VT1, field-effect transistors with an n-channel with a cut-off voltage of not more than 4 V can be used. Bipolar transistor VT2 - any of the KT315 series or similar.

Variable resistors - with a linear regulation characteristic, for example, SPZ-33-32 or similar imported ones.

The dimensions of the printed circuit board and the placement of elements on it depend on the capacitors used; such a node is easy to assemble on a breadboard. In the signal path of the block (C1 - C3, C5, C6, C9, C11), it is desirable to use high-quality film capacitors of the K71-5, K71-7, K73-9, K73-17, K78-2 series. Oxide capacitors C4, C7, SU, C13, C14 - imported (for example, Jamicon) or K50-35, the rest - ceramic K10-17, K10-47 or KM series.

Instead of the LM1040 chip, you can use its close analogue - LM1036, which functionally differs only in the absence of the "Extended stereo" mode; but one should keep in mind the difference between them in the pinout.

The low output resistance of the adjustment unit (about 20 ohms) eliminates the effect on the gain of the UMZCH with a common OOS and phase inversion, even if its input resistance is small - a few kilo-ohms.

The use of electronic regulation in the stereo path makes it possible to abandon dual variable resistors, eliminating the appearance of crackles and rustling during regulation, and increase the service life of the equipment.

Author: N. Tokarev, Moscow; Publication: radioradar.net

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