Color-musical device on fluorescent lamps. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Color-musical device on fluorescent lamps. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Color and music settings

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Several descriptions of various attachments to low-frequency amplifiers have been published in the literature, allowing you to accompany speech and music with color effects. But all these designs have a number of disadvantages. One of them is that incandescent lamps, which are used at the output of color and music installations, have an uneven spectrum of light radiation, therefore, even at full incandescence, the spectrum of the lamp in the blue light region is much weaker than red. With a change in incandescence, not only the intensity of the radiation changes, but also its spectral composition. To obtain the same brightness of different colors, it is necessary to use lamps of different power. In addition, incandescent lamps have a strong nonlinearity in the relationship between the emitted light power and the electrical power consumed.

The second disadvantage of devices of this type is the low output power. Indeed, to light three lamps of 100 watts, a very powerful amplifier and an appropriate power supply are required. Moreover, in the case of using an AC amplifier, it becomes necessary to use three powerful output transformers.

And finally, the third drawback is the flashing effect. It lies in the fact that the radiation intensity of each channel, and hence the total intensity, is proportional to the sound volume. This leads to very sharp fluctuations in light intensity, adversely affecting the audience.

The proposed design of the prefix for color music allows, if not completely eliminating, then significantly reducing these shortcomings. Installation scheme here.

The first problem is solved by replacing incandescent lamps with fluorescent lamps, the spectral composition of light radiation of which is practically independent of intensity. The method of controlling a fluorescent lamp using a high-frequency electromagnetic field (about 20 MHz) is not applicable due to the generated radio interference, while magnetic amplifiers are still little used by radio amateurs. Therefore, a method was chosen to control the intensity of the glow using a DC amplifier.

The output lamp of the amplifier must have an anode current of the order of 0,24 - 0,3 A. This requirement is satisfied by the GU-50 lamp or two 6P3S lamps connected in parallel.

The problem of constant total light intensity can be solved by several methods:

a white background light is introduced, the brightness of which decreases with an increase in the brightness of color sources;
one of the primary colors is used as a background, for example, green, which is given a dominant value; in silent mode, its intensity is maximum. As the intensity of other colors increases, the background color weakens;
all three primary colors (red, green, blue) in silent mode are half the maximum intensity. An increase in voltage in any part of the spectrum leads to an increase in the brightness of the corresponding color and a simultaneous decrease in the brightness of the other two, so that the total light intensity remains constant. When creating the described system, the latter method was chosen.

The low-frequency preamplifier and audio frequency filters are made according to the usual schemes, therefore their descriptions and circuit diagrams are not given in this article.

The output part, the circuit of which is shown in the figure, consists of three identical channels, each of which includes a diode detector (D103), a differential amplifier (6N1P), a final amplifier (GU-50) and a fluorescent lamp of the LDTs-30 type, painted in one from flowers. Rectifiers are common for all three channels.

The audio frequency voltage from the filter output is fed to the corresponding detector. The constant component of the voltage at the output of the detector, approximately equal to the amplitude of the input voltage, is amplified by a differential amplifier (L4, L5 or L6). Two voltages are removed from the outputs of each amplifier, one of which increases, the other decreases in proportion to the input voltage applied to the detector. These voltages and a compensating voltage of -180 V are fed to adders made up of resistors, the outputs of which are connected to the control grids of the GU-50 terminal lamps. Each adder is supplied with an increasing voltage of its channel and decreasing voltages of the other two channels. As a result, for the intensity of the glow of the fluorescent lamp of each channel, you can get the expression:

Ia = K (2a - b - c) + Io
Ib = K (-a -+2b - c) + Io
Ic = K(-a - b + 2c) + Io

where K is the overall gain; Io - the intensity of the glow of a fluorescent lamp in the absence of a signal.

From the expressions obtained, it can be seen that the total intensity of the glow of all three lamps Ia + Ib + Ic = 3 Io is constant and does not depend on the input voltages a, b and c.

The resistances of the resistors of each adder are chosen so that the operating point Io in the absence of a signal corresponds to the middle of the linear section of the characteristic that expresses the dependence of the brightness of the fluorescent lamp on the power consumed, which corresponds to a current through the lamp equal to 150 mA for lamps of the LDC-30 type. The bias voltage on the control grids of the GU-50 should be equal to -30 V.

The GU-50 lamps are connected by triodes in order to reduce their internal resistance and prevent overheating of the screen grids of the lamps in case the LDC-30 lamp does not light up for any reason. For reliable ignition of LDC-30 lamps, in addition to a constant voltage of +300 V, they are additionally supplied with a pulsating voltage with an amplitude of -360 V. The filament voltage to the negative electrode of each fluorescent lamp is supplied from a separate filament winding. A constant voltage of 300 V to power the entire installation is supplied from a transformerless rectifier made on powerful D302 diodes connected in a bridge circuit. The filaments of all amplifying lamps are connected in series and are powered from the mains through a 10 microfarad capacitor.

The power transformer is used only to obtain the filament voltage of fluorescent lamps and negative voltages of -180 V and -360 V. Such a power supply scheme allows the use of a power transformer with a power of about 40 watts. Due to the use of a transformerless rectifier, the connection of the color music set-top box to a radio receiver or tape recorder must be made through a low-frequency transformer. With a mains voltage of 127 V, fluorescent lamps rated for 127 V are used.

The article does not indicate which colors are chosen and what frequencies of the sound range they correspond to, since the concept of low, medium and high frequencies depends significantly on the sound program. Most viewers are in favor of the generally accepted correspondence: low frequencies are red, mids are green or yellow, and highs are blue.

Author: R. Terentiev, V. Psurtsev; Publication: cxem.net

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