Could anybody explain what is the reason to put
such a large capacitor C4 220nF between base of transistors?
Only for stability purpose? If so, why such a large?
Reactance for 1KHz is 720Ω.
I don't use this old circuit. It and a pcb design are shown in the datasheet for the TDA2030A amplifier IC.
The power transistors boost the current of the amplifier IC so that a 4 ohm speaker can be driven with a much higher power.
single supply power amp with a large electrolytic coupling the speaker output...... that's an oldie but moldy....... i still see it done from time to time, but it behaves badly when it clips. this amp could be operated from +/-22V rails, and you could eliminate the output capacitor and the voltage divider that provides +22V on the + input (the three 100k resistors).
the supply current for the chip operates the output transistors, but the supply pins must be well bypassed (but not to ground, as that would defeat the purpose of using the supply pin currents to operate the transistors) for the chip to operate properly. the chip is there primarily for voltage gain (and some current gain) and the output transistors provide most of the current gain. don't try this with an op amp!!!!! most op amps can't be operated above 36V (or +/-18V) and can't source enough current to drive output transistors directly.
also, the supply current for the chip sets the bias for the output transistors, so there's no bias adjustment. this means that most likely the transistors will run a bit hot, since they're probably running a high bias current. the chip will control this to an extent if it's mounted on the same heat sink as the transistors, but it looks like a thermal nightmare....
also, the supply current for the chip sets the bias for the output transistors, so there's no bias adjustment. this means that most likely the transistors will run a bit hot, since they're probably running a high bias current. the chip will control this to an extent if it's mounted on the same heat sink as the transistors, but it looks like a thermal nightmare....
Until the TDA2030 is drawing more than about 900 mA, the current through the output transistors is zero.
When I was in my 20's, I built one of these with a 741 in the middle (different resistor values of course). It was cool. I don't remember if it sounded good.