Circuit power audio amplifier stereo LM1875 + NE5532 – 2 x 20 Watts

Circuit audio amplifier stereo power with LM1875 and preamp for NE5532 - 2 x 20 Watts

The LM1875 is a monolithic power amplifier offering very low distortion and high quality performance for consumer audio applications.
The LM1875 delivers 20 watts into a 4Ω or 8Ω load on ±25V supplies. Using an 8Ω load and ±30V supplies, over 30 watts of power may be delivered. The amplifier is designed to operate with a minimum of external components. Device overload protection consists of both internal current limit and thermal shutdown. The LM1875 design takes advantage of advanced circuit techniques and processing to achieve extremely low distortion levels even at high output power levels. Other outstanding features include high gain, fast slew rate and a wide power bandwidth, large output voltage swing, high current capability, and a very wide supply range. The amplifier is internally compensated and stable for gains of 10 or greater.

Circuit description of the power audio amplifier with LM1875n

The scheme is simple and can be divided into three parts: Power supply, preamplifier and stereo power amplifier.

Power supply: This power supply is symmetrical, easy assembly, the transformer must be 60VA 18-0-18 volts in the secondary to have a maximum of + – 25 volts at the power supply, if you use speakers of 8 ohms can use up to 22 volt transformer and thus will have about 30 watts per channel. B1 is a bridge rectifier that must withstand 100 volts / 4 A, ex: GBU606. The capacitors C2 and C5 can be longer if you prefer, the power supply for the preamplifier circuit is based on the integrated voltage regulators 7815 and 7915, beyond the initial source of the capacitors, there are number of capacitors on supply lines of integrated circuits .

Pre Amplifier: This circuit is based on double operational amplifier NE5532N. The audio is coupled by C26, until the pin 3 of ic5A is amplified and coupled via C25 to IC4 LM1875. In the right channel is the same thing.

Stereo Power Amplifier: This circuit is based on two integrated circuit LM1875 audio amplifiers that allow amplification of up to 20 watts per channel or 30 Watts maximum @ 8 ohms @ +-30Volts,  are connected to speakers 40 Watts RMS.

Schematic diagram of a stereo amplifier using integrated circuit lm1875 – click to enlarge

Board component side – guidance for mounting the circuit with lm 1875 – click to enlarge

Board Copper bottom side

Copper board component-side

For those who do not want to use double-sided board, make red marks on the connection wires

List of components for assembly of the stereo amplifier chip LM1875

Part Value Description Amount
Resistors 1/4W 5%
R1, R7 12k Brown, Black, Orange, Gold 2
R2, R9, R16, R17 1k Brown, Black, Red, Gold 4
R3, R4, R8, R10, R11, R14 22k Red, Red, Orange, Gold 6
R5, R13 10k Brown, Black, Orange, Gold 2
R6, R12 1 Ohm /1W Brown, Black, Gold, Gold 2
C1, C3, C6, C8, C11, C17, C21, C27 100nF Ceramic Capacitor 8
C2, C5 4700uF/35V or 6800uF Electrolytic Capacitor 2
C4, C7, C10, C18, C20, C28 100uF/35V Electrolytic Capacitor 6
C9, C12, C19, C22 22uF/35V Electrolytic Capacitor 4
C13, C23 220nF/100V Ceramic Capacitor or polyester 2
C14, C24, C29, C30 220pF Ceramic Capacitor 4
C15, C25 2.2uF/35V Electrolytic Capacitor 2
C16, C26 10uF/35V Electrolytic Capacitor 2
IC1 LM7915 Negative voltage regulator -15V 1
IC2 LM7815 Positive voltage regulator +15V 1
IC3, IC4 LM1875T – TO-220 Audio Amplifier – Texas Instruments 2
IC5 NE5532 or equivalent Dual OP AMP 1
B1 KBL608 or equivalent Rectifier bridge 1
LED1, LED2 Led 5mm Red LEDs 2
TRAFO 3 pin KRE Connector Terminal Power – Connect the transformer 1
IN 3 pin KRE Connector Terminal Audio input 1
OUTL 2 pin KRE Connector Terminal Left channel audio output 1
OUTR 2 pin KRE Connector Terminal Right channel audio output 1
Welding, Wire, PCB, Box.

Download Circuits files in Eagle PDF: Lm1875 PCB, Schematic, Silk Screen, component side.
Download   Mirror

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About the author blog author. Electronics technician for the technical school of Brasilia - Brazil. Interested in electronics, circuits and technology in general.

11 thoughts on “Circuit power audio amplifier stereo LM1875 + NE5532 – 2 x 20 Watts”

  1. Hey man there’s a mistake, the virtual photo you made of the assembly amplifier is incorrect, all the pcb is in inverted possition, this caused i made the pcb again, please check it!

  2. [img][/img]
    the upper picture No connection to speaker out to GND, but connect to gnd below picture


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