Three-channel automotive ULF on TDA1518BQ chips. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Three-channel automotive ULF on TDA1518BQ chips. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Automotive power amplifiers

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When the sound of the small Sony in front and Kenwood in the rear in the regular trunk space ceased to please the ear, I thought about improving the sound quality in the car. The option "to embed a couple of pancakes into the rear shelf" seemed the simplest, but the popularity of such acoustics among car thieves was embarrassing, and besides, the price of good pancakes was about $100. After listening to how other people play the channel separation system and studying the theory in Radio magazines, I came to the conclusion that a three-channel system would be the most rational for use in a limited enclosed space of a passenger car.

Firstly, because it is much easier to find a place for one powerful and high-quality low-frequency head (or speaker system) than for two, and secondly, good mid-high-frequency speakers, in this case, can be small and efficient at the same time. I note that at that time I had not yet heard how amplifiers with a power supply play, rocking a real subwoofer ... But more on that later.

A schematic diagram of such a three-channel amplifier is shown in the figure.

Three-channel automotive ULF on TDA1518BQ chips

Amplifier parameters

Total range of reproducible frequencies, Hz	12 - 20000
Maximum output power (THD=10%, Rн=4 Ohm, Up=14V)
MF-HF channels	2x12W
LF channel	24w
Rated power (THD=0.2%)
MF-HF channels	2x8W
LF channel	14w
Maximum current consumption	8А

As active elements, two TDA1518BQ microcircuits were used, containing a pair of low-frequency amplifiers each, developing power up to 12W at a 4-ohm load. The microcircuit can work as a set of two amplifiers for stereo channels, and as a single-channel bridged amplifier, it all depends on the connection of its outputs and on which inputs the signal is applied. In bridging, the microcircuit develops power up to 24W at the same load. In the described UMZCH, one A1 chip works as a stereo amplifier for midrange-high channels, and the second A2 works as a powerful ultrasonic frequency channel. Technical description for IC TDA1518BQ here.

The stereo signal is received through connector X1. Variable resistors R1 and R2 are used to set the levels of the stereo balance and the level of the mid-high channels. Stereo signals through capacitors C1 and C2 of relatively small capacity are fed to the inputs of two UMZCH, which are included in A1. The inputs are in-phase, since the microcircuit operates in two-channel amplifier mode. The choice of the operating mode (two-channel or bridge amplifier) for microcircuits of the TDA1518 type is made by closing one of the inputs of the upper, according to the scheme, the UMZCH microcircuit to pin 4. This UMZCH has two inputs - direct - pin 1, and inverse - pin 2. If you need a two-channel amplifier pin 2 is connected to pin 4, and pin 1 is signaled if a bridge amplifier is required, pin 4 is connected to pin 1, and pin 2 is connected to pin 13 (direct input of the second UMZCH). Partial blockage of low frequencies occurs at the input - C1 and C2 of too low capacity, the main blockage of low frequencies - at the output, due to simple high-pass filters formed by low-capacity separating capacitors C4 and C5, resistors R6 and R7, and speaker coil resistances.

The crossover frequency is about 400 Hz. The low-frequency channel is made on the A2 chip. The adder, which forms a monophonic signal from a stereo signal, consists of resistors R3-R4, which, together with the capacitor C10, are a simple preliminary low-pass filter that slightly fills the mid-high frequencies. A mono signal is formed on a variable resistor R5, which serves to set the level of the low-frequency channel. Chip A2 is connected in a bridge circuit. The absence of a separating capacitor at its output contributes to high-quality reproduction of low frequencies, and the output low-pass filter, consisting of coils L1, L2, the resistance of the low-frequency speaker VZ and the capacitance C8-C9 connected in parallel to it, provides a deep blockage of frequencies above 500-600 Hz.

Due to the fact that the amplifier consumes high current, there is no switch in the power circuit, UMZCH is constantly connected to the on-board network, but when S1 is opened, it goes into standby mode, in which it does not function and consumes less than 1 mA current. In my version, the +12 V voltage is supplied to the terminals of 11 microcircuits through a 0.5A fuse from the antenna output of the radio.

Coils L1 and L2 are wound on sections of cylinders of disposable syringes with a diameter of 23 mm, each contain 150 turns of PEV-0,61 wire. Coils together with capacitors C8, C9, R8 are located next to the woofer.

As a housing - radiator for UMZCH, you can use the housing from a faulty switch of the non-contact ignition system. Chips TDA1518BQ can be replaced by TDA1516BQ or TDA1516CQ, which have the same pinouts, but differ in input sensitivity. Woofer - 35GDN1-4, each mid-high speaker - 13 cm two-way Kenwood.

In the power supply circuit of the amplifier, there must be an LC filter, a 10A fuse. To reduce interference from a running engine, I disconnected the "mass" of the radio from the car body, removed the "grounding" of the antenna feeder on the deflector, connected the "body" of the amplifier to the "case" wire of the low-pass filter (the output of the resistor R8, left according to the diagram), and only to This point connected the wire connecting the "mass" of the car with the "body" wire of the entire audio system. "Mass" is fed to the radio through the screen of the line-in cord connecting the radio to the amplifier. When pulling this cord through half of the car, it is necessary to ensure that its screen does not touch any metal parts of the car that can "ground" it. Yes, and the acoustic output of the rear speakers is used as a line output on my radio.

The location of the speakers in the car

Front: Two-way Sony are in the front doors, connected in parallel to the tweeters located on the A-pillars. Rear: The woofer is located in the center of the trunk shelf, reinforced with 7 mm thick plywood, the midrange and tweeters are located in the regular places of the trunk. The amplifier housing, the filter board for the low-frequency channel are screwed to plywood, which reinforces the rigidity of the trunk shelf.

Publication: cxem.net

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