Color and music setup with two-stage brightness control. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Color and music setup with two-stage brightness control. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Color and music installations, garlands

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The dynamic range of incandescent lamps is much narrower than that of a piece of music. This leads to the fact that the color-music device tuned to the maximum incoming signal level (DMU) stops working at low signal levels. If the CMU is set to the minimum signal level, then at medium and maximum signal levels, the intensity of the glow of incandescent lamps is constant. As a result of this, a blinking effect occurs, which quickly tires the listener and does not correspond to the nature of the phonogram.

Special devices help to eliminate this contradiction - compressors and automatic gain controls, which allow narrowing the dynamic range of a musical work to the dynamic range of incandescent lamps (5 ... ... 10 dB). However, it is possible to match the dynamic ranges of the DMU and phonogram signals using multi-stage brightness control.

(click to enlarge)

The diagram shows only the low-frequency channel of the DMU. The input signal, as usual, is divided by filters into the corresponding number of frequency channels. The filters of each channel are made of two independent LC circuits (L1C1 and L2C2). The first stage of the regulator is assembled on transistors V1 and V2, a parallel group of lamps H2 is included in the emitter circuit of transistor V1. The lamps of this group operate when the amplitude of the input signal changes from 0,5 to 3 V. This range can be slightly changed with the potentiometer R1. When the contacts of the switch S1 are open and the amplitude of the input signal increases by more than 3 V, the second DMU circuit (V3, V6, H2) is activated and the group of H2 lamps immediately turns on to full heat, displaying the amplitude signal spikes at the frequencies of the corresponding channel. In the closed position of switch S1, the lamps of this group begin to glow at an input signal level of 1 V. A backlight channel is assembled on the trinistor V10. The background channel works in conjunction with the first stage and turns off when the lamps of the second group of any of the channels are turned on.

The device is powered by a 6,3 V alternating current source. The input of the device is connected to the output of an audio frequency amplifier with a power of 4 ... 6 W. The Control button allows you to check the operability of the second stage and the background channel. The frequency band in the CMU is divided into three frequency channels: 100...350, 350...700, 700...2000 Hz. The filter coils of all channels are the same, have an inductance of about 1 H, contain 1000 turns each and are wound with PEV-2 0,15 wire on a K20x12x6 ring magnetic circuit made of 2000NM ferrite. Capacitors C1 and C2 in the channels have a capacity of 0,47; 0,1 and 0,02 uF, respectively, for each of the frequency channels. Screen device housing 400x300x120 mm. The screen is made of cellular transparent material. Closer to the screen are the lamps of the first stage, the side walls are pasted over with crumpled aluminum foil, and the back wall has a dark background, which changes the apparent depth of the screen. For a frequency channel of 100 ... ... 350 Hz, two lamps of the first stage and four lamps of the second are painted green, and one lamp of the second stage is red and yellow. For the frequency channel 350 ... 700 Hz, two lamps of the first stage and four lamps of the second are painted red and one lamp of the second stage is green and blue. For the frequency channel 700 ... 2000 Hz, three lamps of the first stage and six lamps of the second are colored blue, and two more lamps of the second stage are yellow. Background lamps (5 pieces) are colored differently and are placed over the entire area of the rear wall.

To configure the DMU, an audio frequency generator with a low-impedance output of 50 ohms is connected to its input. When the device is powered on, all background lamps should light up. The sensitivity of the channels is set to a minimum and the resistors R2 are adjusted until a weak glow of the lamps of the first stages is obtained. By adjusting the resistor R13, they ensure that when the channel button S2 is turned on, the second stage lamps turn on and the background lamps turn off. Then, having increased the sensitivity of the channels to the maximum, signals of various frequencies, with an amplitude of 1 and 3 V, are supplied from the generator and the operation of the DMU is checked. If necessary, select resistors R6 and R7 and filter capacitors C1 and C2.

Author: V.Gromov

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