UMZCH for automotive radio equipment. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Automotive power amplifiers
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Readers are invited to a power amplifier for automotive audio equipment. During its development, the author tried to create a compact amplifier with good sound reproduction quality and high reliability when it is used in the specific conditions of a car interior.
The amplifier has the following main specifications:
- rated output power at a load with a resistance of 4 ohms - 2x15 W;
- range of reproducible sound frequencies - 20...20 000 Hz;
- harmonic coefficient at rated output power - no more than 0,3%;
- bass tone control range - from -19 to +17 dB at a frequency of 40 Hz and treble tone ±15 dB at a frequency of 16 kHz.
The amplifier is powered by 13,4 V car batteries.
The amplifier (Fig. 1) is assembled on four foreign-made microcircuits and one domestic one: DA1, DA2 work in the input signal level indicator, DA3 stabilizes their supply voltage; a timbre block is assembled on DA4, a power amplifier is assembled on DA5. The volume is controlled by resistor R6, LF tone - R9, HF tone - R8, stereo balance - R7.
(click to enlarge)
The amplifier is made in the form of a functionally complete compact unit and contains a minimum number of mechanical parts. The bearing part of the entire structure is a heat sink with an area of 200 cm2, made of duralumin 2 mm thick. The printed circuit board is made of foil fiberglass with a thickness of 1,5 mm. Its dimensions are 130x90mm.
The location of the parts on the printed circuit board is illustrated by a photograph (Fig. 2).
The amplifier uses fixed resistors MLT-0,125 (R1 - R5, R14, R15) and MLT-0,25 (the rest); variables (R6 - R9) - SPZ-4aM, tuning - SPZ-38G (R10, R11). Oxide capacitors are imported analogues - K50-35, the rest - KM-5. Choke L1 - from any domestic car tape recorder.
Establishing UMZCH comes down to the selection of resistors R1 and R2, which ensure reliable operation of the input signal indicators.
When connecting loudspeaker heads to the amplifier, you should pay attention to their correct (common-mode) inclusion. In-phase inclusion corresponds to a higher total sound pressure at low sound frequencies.
Author: A. Levashov, Kizlyar, Dagestan
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