This final 4 channel amplifier is really designed for automotive use, but of course it can also be used for many other medium power applications. The TDA7375A can be successfully used in any situation where a reasonable amount of audio power is required and only a relatively low supply voltage is available. This IC is the successor to the TDA7374B, which forms the heart of the active speaker system described earlier this year. Such quad-amplifier ICs are naturally an excellent choice for this application, especially since the individual amplifiers can be connected in pairs in a bridged configuration, allowing them to provide power. four times.
The new IC can handle a peak voltage of 50V (10V higher than the TDA7374B), but more importantly, it is also really intended for single-ended operation. It includes every kind of protection imaginable to prevent premature failure of all four amplifiers, and it's, in fact, perfectly suited to "obvious" mini surround sound systems. For more information about the TDA7375A, we refer you to its data sheet, available at www.st.com. The circuit shown here has four potentiometers to individually adjust the output level of the amplifier. In addition, all inputs have an RC network (R1/C1, etc.) to block possible RF interference.
The function of R6 is to separate the background of the input and output stages, to avoid possible ground loops when using some modules. 5W type is used for this resistor to prevent the resistor from fuming if the grounding connection of the power supply is loose. C10 decouples the internal voltage divider, which biases the internal amplifier stages to half the mains voltage. The R5/C9 RC network provides slow, hang-free booting. C15 and C16 are local bypass capacitors for mains voltage. The TDA7375A's supply ripple rejection is about 50 dB. If you only want to use transformers, bridge rectifiers, and smoothing capacitors for power, the minimum requirement is a 12 V/30 VA transformer combined with a 10,000 µF electrolytic capacitor (remember that the maximum allowable supply voltage is 18 V).
One of the few downsides of this quadruple amplifier is that two of the channels are inverted compared to the other two. For this reason, the polarity of each speaker terminal is marked on the PCB diagram (e.g. +LS1 and –LS4) to indicate which speaker terminal should be connected to where. Radial electrolytic capacitors rated 3300 µF/16 V and measuring only 12 mm in diameter are used for the output capacitors, which allows the board to remain relatively compact. Our favorite type of capacitor is a member of the Rubycon ZL series, which can handle ripple currents of no less than 3.4 A. The maximum circuit current with all four channels driven at cutoff (with 4 Ω load) is approximately 2.1 A.
The TDA7375A can also be used with 2 Ω loads. However, in this case, the internal temperature increases significantly because the 15V Multiwatt package has a rather large thermal impedance of 1.8 ºC/W. For the sake of the life of the integrated circuit, it is therefore advisable to use a slightly larger heat sink. The 4 A/T fuse has been selected taking into account its ability to operate at 2 Ω. If you limit the load to 4 Ω, the fuse value can drop to 2 A/T. The amplifier outputs are on the board next to the included electrolytic capacitors. The relevant ground connections for LS1 and LS2 are located next to the LS1 and LS2 terminals, but the ground connections for LS3 and LS4 are located to the left, next to the IC, as this yields current paths. Best on PCB and smallest distortion. Vertical car connector (flat connector) is used to connect power.
COMPONENTS LIST
Resistors:
R1-R4 = 100Ω
R5 = 10kΩ
R6 = 0Ω1, 5W
P1-P4 = 10k preset
Capacitors:
C1,C3,C5,C7 = 15nF
C2,C4,C6,C8 = 220nF
C9 = 10µF 63V radial
C10 = 47µF 25V radial
C11-C14 = 3300µF 16V
radial, max. diameter 13mm, e.g., Panasonic
(Iripple 2500 mA) or Rubycon (Iripple 3400 mA)
C15 = 100nF
C16 = 1000µF 25V radial, max. diameter 13mm
Semiconductors:
IC1 = TDA7375A (ST)
Miscellaneous:
F1 = fuse, 4A/T (time lag), with PCB mount holder 2 fast-on (spade) terminal, male, vertical, solder type (2-pin version)
Measurement results
Supply voltage = 14.4 V
Quiescent current = 100 mA
Pmax. (0.1% THD) = 4 x 5.3 W/ 4Ω
Input sensitivity = (5.2 W/4 Ω) 0.5 V
THD+N (B = 80 kHz, 1 kHz 1W/4 Ω) = < 0.04 %
Bandwidth = 28 Hz to 55 kHz