This useful amplifier will provide an output power of up to about 8 watts rms at low distortion (less than 0.1% THD) into an 8 ohm loudspeaker when using a 28 volt supply. If used with a 4 ohm loud­speaker the output power is in­creased to about 12 watts rms or so, with the distortion being roughly doubled (although ob­viously still quite low). The circuit will operate with lower supply voltages, down to less than 9 volts, with a reduction in the maxi­mum output power.

Circuit in lines (Click to enlarge)

The circuit utilizes a TDA2030 integrated circuit, a modern device superior in performance and ea­sier to use than most previous de­vices. It is used in much the same way as an operational amplifier, and like an operational amplifier it has both inverting (—) and non-invert­ing (+) inputs. In this circuit it is used in the inverting amplifier mode.

The non-inverting input is biased to half the supply potential by R2 and R3; C2 decouples any hum or other noise from the supply lines. R4 biases the invert­ing input of ICI, with a negative feedback action stabilizing the output at half the supply voltage under quiescent conditions. This ensures that the circuit can provide the highest possible un­clipped peak to peak output voltage swing (and output power).

R4 also forms part of the network which sets the gain and input impedance of the circuit, with R1 forming the other half. The voltage gain is approximately equal to R4 divided by R1, about 30 with the specified values. This gives the circuit an input sensitiv­ity of about 260mV rms for 8 watts into 8 ohms. The value of R1 sets the input impedance of the amplifier at 22k, but volume control VR1 shunts the input to give a minimum input impedance of 11KR.

Input and output DC blocking are given by C1 and C4 respecti­vely. C3 and R5 are a Zobel net­work and aid the stability of the circuit. C5 provides supply decou­pling and should be mounted close to ICI.

Regards

Team Coreelectronics