Amateur amplifier control unit. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Amateur amplifier control unit. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Transistor power amplifiers

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The article describes the design of the block of electronic adjustments, which includes an input selector, volume controls with switchable loudness, balance and tone for low and high frequencies. The author assembled this block on the basis of a modern LM1036N microcircuit, the advantage of which is small non-linear distortions. Such an assembly can be used both in a complete (integrated) amplifier and in a separate preamplifier design.

The modern market for radio elements offers highly integrated microcircuits, and the assembly of many electronic devices has now become an easy task. This is especially important for beginner radio amateurs who do not have experience in manufacturing complex structures. It is also attractive that with proper installation, the structures begin to work immediately and practically do not require adjustment.

Recently, designs of various ultrasonic frequencies have gained great popularity to amplify the signal from a computer sound card, CD player and other sources of sound programs. But most of the circuits of such devices given in various literature either do not contain adjustments, except for the volume control, or they use outdated microcircuits with electronic control, which degrade the sound even when high-quality UMZCH microcircuits are used.

As an experiment, three versions of the adjustment block were made on various microcircuits, included according to the manufacturer's standard schemes. Then the quality of sound reproduction was listened to on music of various genres with these blocks as part of the same tract. Friends and acquaintances were invited to audition as experts. At the same time, measuring instruments were not deliberately used, the entire examination was carried out according to the "blind" method.

Almost everyone noted shortcomings in the sound of devices assembled on KR174XA54 microcircuits (in a block with electronic push-button control) and TDA1524 (adjustment with variable DC voltage). With good declared parameters, the sound took on an artificial character even with neutral settings of the regulators (without frequency correction - "flat"). The typical inflection frequencies in the tone controls and loudness circuits were chosen extremely poorly for these microcircuits; when adjusted, "mumbling" appeared at low frequencies.

The absolute winner of the test was the LM1036N chip. The experts noted a clear, light sound and correctly acting loudness when adjusting the volume. At the same time, the microcircuit has a low cost (about 60 rubles) and is not in short supply.

The adjustment block (its diagram is shown in Fig. 1) for the ultrasonic frequency converter includes an input selector, volume, balance and tone control for low and high frequencies. There is also a mode for turning on tone compensation when adjusting the volume. The signal source is selected using a switch on the electromagnetic relays, which, with electronic adjustment of sound settings, allows you to place the printed circuit board and related components in close proximity to the amplifier inputs. This minimizes noise and AC noise.

(click to enlarge)

The characteristics of the adjustment block are determined by the applied microcircuit. According to the manufacturer (National Semiconductor Corporation), the LM1036N chip has the following characteristics:

Frequency range at unevenness ±0,1 dB, Hz......20...20000
Signal-to-noise ratio, dB......80
Channel separation, dB ...... 75
Harmonic coefficient at UBX=0,3 V at a frequency of 1 kHz, %......0,06
Input impedance, kOhm......30
Output impedance, Ohm......20
Volume control range, dB ...... 75
Balance adjustment range, dB......26
Tone control range at 40 Hz and 16 kHz, dB......±15
Current consumption at supply voltage 9... 16 V, mA, no more......45

The adjustment block is mounted mainly on a printed circuit board (Fig. 2) with dimensions of 53x55 mm made of fiberglass laminated on both sides. It contains all the elements, except for the input selector, variable resistors R8-R11 and switch SA1. The mounting holes on the part installation side are countersunk to prevent short circuits, and the foil used to reduce pickups on the board and the common wire circuit is connected to the common wire.

Amateur amplifier control unit

In the design, you can use fixed resistors MLT-0,125, capacitors K73-17 or similar imported elements. Oxide capacitors - K50-35 with an operating voltage of at least 16 V or similar. As regulators R8-R11, imported dual variable resistors with a linear regulation characteristic are recommended; you can also use domestic variable resistors of group A of any type with a resistance of 22 - 47 kOhm. Dual resistor sections are connected in parallel for increased reliability.

The K1-KZ relay of the input selector must have the appropriate groups of contacts and an actuation voltage of 8 ... 10 V. The SA1 switch is of the P2G-3 type with a weakened latch spring and a remote limiter for circular movement (as in imported amplifiers). Input connectors - any used in consumer audio equipment (ONTs-VG, "tulips", SCART). RES-47 relays (passport 4.500.408) were used as signal source switches. The choice is due to the presence of two groups of contacts and the sealed design of the relay. We can also recommend relays RES-47 (passport 4 500 419), RES-48 (passport 4.590.204), RES-59 (passport 4.500.020), having a similar design. Relay housings should be connected to the common wire of the device.

The proposed adjustment block can be used, for example, in conjunction with UMZCH on TDA7294 chips (see "Radio", 2000, No. 5, pp. 19-21).

Author: O.Kornilov, Pechora, Arkhangelsk region.

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