This is a high impedance small amplifier circuit. It can give power output about 1W with connecting to a 9V power supply. The advantage of this circuit is using dual Darlington transistors. So they have more size of input impedance about 20 Mega ohms.
This circuit is unlike other circuits. The input impedance is always a constant of about 20 Megohms. Whether we will adjust the volume control on any levels.
Look at the circuit below.
The components in the circuit, they are so cheap.
Especially the all transistors output, BC549, and BC559. So, if we increase the power. They may be very distorted. We must reduce the current level to a safe. By reducing the volume down.
The output section is the R1 and C1 in order. To reduce the oscillator gain. In fact, the output sector, including an op-amp 741 acts as drive dual complementary.
Read more 741 0p-amp circuits
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Generally in work learning of transistor. Also, it is a High impedance small amplifier circuit. We can divide the work period of the transistor are 3 the period.
For example, the period cut off be transistor stop work. At this period have no bass current (Ib) and collector current (lc). The period is full be intermittently at current flow through with full ahead.
Until reach the condition is full and the trend will don’t flow increase back and forth the reed that the this.
And the period active be intermittently at transistor work Bias current.
We can find a gain ratio value current. Thus in using transistor power amplifier, as a result, will very the circuit work during active.
Which we will live expansion ratio way value current of the transistor.
There are R1 and R2 to build a divide bias voltage. To give Q1 by having a signal output at collector pin (C). But a signal has still not enough.
Then, we must induce to amplify with Q2 and Q3 again.
Which Q2 and Q3 each other be Darlington circuit be the lead transistor 2 pcs.
They have alike property comes to each other.
They will get the gain rate rises.
From that time a signal that enlarged reach a loudspeaker SP1 makes a louder sound out.
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