Tone block with fixed settings. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Tone block with fixed settings. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Audio equipment

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Automation of control of operating modes in modern radio-electronic equipment makes it possible to optimally select the most acceptable operating modes with minimal time expenditure. This is very clearly visible in the evolution of tone control control units in sound reinforcement equipment, which have gone from a conventional variable resistor, through specialized mechanical keyboard stations with a fixed selection, to electronic control with just one button, without losing the property of multi-position selection. In addition, such a one-button control system opens up broad horizons for the creation of remote control systems.

As is known, the timbre coloring of a reproduced audio frequency signal (3H) very much depends on the quality of the equipment, speaker systems, room acoustics and other factors. Therefore, the vast majority of household equipment contains devices that allow you to change the amplitude-frequency response (AFC) of a 3H signal to your liking. These are usually simple tone blocks or equalizers that allow you to smoothly adjust the frequency response in two or more frequency bands. But, as practice shows, most listeners most often choose only a few positions of the frequency response regulators. Therefore, devices with smooth adjustment are not always justified.

It is for this reason that in middle-class equipment they began to use tone blocks with fixed frequency response shapes. Usually there are from 4 to 6 such fixed settings. The listener can quickly select one of them by simply pressing a button, which, of course, is very convenient when using the equipment. There are specialized microcircuits that allow you to assemble such a device [1]. The magazine "Radio" published similar homemade designs of tone blocks with fixed settings, for example [2].

I would like to offer another version of the device, which allows you to select one of four frequency response waveforms that can be pre-configured. Its diagram is shown in the figure.

(click to enlarge)

The basis of the tone block is the DA1 chip type TDA1524A (Philips). It acts as an electronic volume and tone control [3]. The inclusion of this microcircuit is typical. Variable resistor R10 regulates the volume, i.e., the signal level at the outputs of the microcircuit (pins 8 and 11), and resistor R9 regulates the balance between stereo channels. There are no variable resistors for adjusting the bass and treble tones. Instead, a tone control device on DD1-DD3 chips is included. The device works as follows.

When turned on for the first time, the DD1 counter will be set to zero by a voltage pulse generated by the R3C1 circuit. At pin 3 of the counter there will be a log level. 1, on the rest - log level. 0. Inverter DD2.3 (the top of the four) will go into the log state. 0 at the output (pin 6). The HL1 LED turns on, signaling the activation of mode "1". At pins 10 and 9 of the DD3 multiplexer there will be log levels. 0. Therefore, inputs X (pin 13) and Y (pin 3) will be connected to inputs X0 (pin 12) and Y0 (pin 1), respectively.

Pin 9 of the DA1 chip will receive the low-frequency tone adjustment voltage from the trimmer resistor R11, and pin 10 will receive the high-frequency tone adjustment voltage from resistor R15. By changing the positions of the sliders of these trimming resistors, you can select the desired frequency response in this mode of operation of the tone block. Conventionally, we will designate this mode as “FLAT”, i.e. with a flat frequency response.

When you press the SB1 button, a high voltage level through the contact bounce suppressor on the inverters DD2.1 and DD2.2, which is a repeater with capacitive feedback through capacitor C2, is sent to the counting input of the counter DD1 (pin 14). The counter will go into log state. 1 on pin 2. The HL2 LED will light up (mode “2”). Using diodes VD2-VD5 and resistors R7 and R8, a signal converter from the outputs of the counter DD1 into binary code is assembled to control the multiplexer DD3. Therefore, the multiplexer will go to the next state and connect trimming resistors R1 and R12 to the DA16 chip, which should also be configured to receive a certain frequency response of the output signal. Conventionally, this mode is indicated as “ROCK”, i.e. raising the low-frequency and high-frequency components.

With subsequent presses of the SB1 button, pairs of resistors R13, R17 and R14, R18 will be connected in series, which, in turn, are used by other companies to adjust the frequency response. Conventionally, these are the “POP” and “JAZZ” modes, this is signaled by the LEDs HL3 and HL4, respectively.

When you next press the button, a high voltage level from pin 10 of the DD1 microcircuit will flow through the diode VD1 to pin 15 and return the counter and the entire device to its original state, to the “FLAT” mode. Thus, the four modes are switched in a ring with one button, which allows you to quickly select the desired timbre coloring of the sound of the 3H signal. With trimming resistors R11-R14 (LF) and R15-R18 (HF), the timbre block can be configured to any desired shape of the frequency response in each mode. In addition, these settings can be easily changed over time. Therefore, this tone block occupies a middle position between tone blocks with smooth tuning and fixed ones. In addition, it allows you to control the volume and stereo balance between channels. All input and output characteristics of this device correspond to the characteristics of the DA1 chip [3].

As a DA1 microcircuit, you can use the domestic analog K176ХА48, the imported TDA1526A, as well as the TDA1074A tone control only in the appropriate connection. In the latter case, the functions of the volume and balance controls will be absent. Instead of the indicated microcircuits DD1-DD3, you can use similar ones from the K176, K564, KR1561 series. LEDs HL1-HL4 - AL307BM or any others with the desired glow color, diodes VD1 -VD5 any of the KD521, KD522, KD503 series, etc. Resistors and capacitors are also any small-sized domestic or imported.

Setting up the tone block consists of matching the maximum signal level from the outputs of the DA1 microcircuit with the input of the subsequent UMZCH using adjusted resistors R19 and R20. Adjusted resistors R11-R14 and R15-R18 adjust, as mentioned above, the desired shape of the frequency response in each mode of the LF and HF signals, respectively.

Literature

Brylov V. Equalizers of sound signals. - Radio, 2000, No. 8, p. 15, 16; No. 9, p. 13, 14.
Shubin S. Three-band timbre switch. - Radio. 2001, no. 9, p. 54.
Turuta E. F. Low frequency preamplifiers. Volume and tone controls. Display amplifiers. - M.: DMK, 2000, p. 105, 106.

Author: I.Potachin, Fokino, Bryansk region

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