100W Quad Car Amplifier – Schematic Diagrams

100W Quad Car Amplifier Schematic Diagrams      Comments Off on 100W Quad Car Amplifier ]]>

This quad final amplifier
is actually intended to be used in a car, but it can naturally also be
used for a variety of other medium-power applications. The TDA7375A can
be successfully used in all situations in which a reasonable amount of
audio power is desired and only a relatively low supply voltage is
available. This IC is the successor to the TDA7374B, which forms the
heart of the active loudspeaker system described earlier this year. Such
a quad IC amplifier is naturally an excellent choice for this
application, especially since the individual amplifiers can be connected
in pairs in the bridge configuration, which allows them to provide
approximately four times as much power.

The new IC can handle a peak voltage of 50 V (10 V more than the
TDA7374B), but what is more important is that it is also truly intended
to be used for single-ended operation. It includes all imaginable types
of protection in order to avoid the premature demise of the four
amplifiers, and in fact it is ideally suitable for a ‘no-nonsense’ mini
surround-sound system. For more information about the TDA7375A, we refer
you to its data sheet, which can be found at http://www.st.com. The circuit shown here has four trimpots for individually setting the output levels of the amplifiers.

In addition, all inputs have RC networks (R1/C1, etc.) to block
possible RF interference. The function of R6 is to separate the grounds
of the input and output stages, in order to avoid possible ground loops
that might arise with the use of multiple modules. A 5-W type is used
for this resistor, in order to prevent it from going up in smoke if the
ground connection of the power supply comes loose. C10 decouples the
internal voltage divider, which biases the internal amplifier stages to
half of the supply voltage. RC network R5/C9 provides a delayed,
plop-free switch-on.

C15 and C16 are local bypass capacitors for the supply voltage. The
power supply ripple rejection of the TDA7375A is approximately 50 dB. If
you want to use only a transformer, bridge rectifier and smoothing
capacitor for the power supply, the minimum requirement is a transformer
rated at 12 V / 30 VA in combination with a 10,000-µF electrolytic
capacitor (remember that the maximum allowable supply voltage is 18 V).
One of the few drawbacks of this quad amplifier is that two of the
channels are inverted with respect to the other two. For this reason,
the polarity of each loudspeaker terminal is marked on the circuit board
layout (e.g., +LS1 and –LS4) to indicate which terminal of the
loudspeaker should be connected where.

Radial electrolytic capacitors rated at 3300µF/16V and having a
diameter of only 12 mm are used for the output capacitors, which allows
the circuit board to remain relatively compact. Our preferred type of
electrolytic capacitor is a member of the Rubycon ZL series, which can
handle no less than 3.4 A of ripple current. The maximum current
consumption of the circuit with all four channels driven to the clipping
level (with 4-Ω loads) is approximately 2.1 A. The TDA7375A can also be
used with 2-Ω loads. However, in this case the internal temperature
rises considerably, since the Multiwatt 15V package has a rather large
thermal impedance of 1.8 ºC/W.

In the interest of the service life of the IC, it is thus a good
idea to use a somewhat larger heat sink. A 4 A/T fuse has been selected
in consideration of possible 2-Ω operation. If you limit the load to 4
Ω, the fuse value can be reduced to 2 A/T. The output terminals of the
amplifiers can be found on the circuit board next to the associated
electrolytic capacitors. The related 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 on the left, next to the IC,
since this gives the best current paths on the circuit board and the
least distortion. Vertical car connectors (spade terminals) are used for
the power supply connections.

R1-R4 = 100Ω
R5 = 10kΩ
R6 = 0Ω1, 5W
P1-P4 = 10 k preset

C1,C3,C5,C7 = 15nF
C2,C4,C6,C8 = 220nF
C9 = 10µF 63V radial
C10 = 47µF 25V radial
C11-C14 = 3300µF 16V
C15 = 100nF
C16 = 1000µF 25V radial, max. diameter 13mm

IC1 = TDA7375A (ST)

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 × 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

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