The diagram presented below shows a simple circuit of a bird sound generator. All the parts are very common and the transformer is an ordinary type as found in small transistor radios at the output stage
The circuit is basically a feedback oscillator circuit that is configured around a small output transformer. The transistor forms the main active components here.
When mains power os applied to the circuit, the 4K7 resistor resists the voltage and drops it to lower levels suitable for operating the DC electronic circuit.
The diode rectified the low level AC to DC while the capacitor filters and smoothens the rectified DC.
Initially the voltage reaches the base of the transistor which instantly conducts and pulls the one half winding of the transformer to ground, forcing a strong induced current across the secondary winding.
However the moment this happens, the entire voltage is shorted to ground via the transformer winding and this eliminates any biasing voltage at the the base of the transistor and it fails to support the conduction.
The transistor releases the transformer activation which reverts a strong back emf to the secondary winding.
However the moment the transistor stops conducting, the voltage at it's base is restored and the cycle repeats again.
This repeated pulsation of the transformer induces a strong back emf oscillation at the secondary of the transformer, which is amplified over the connected loudspeaker.
The associated components, the 10 resistor and the 0.1 capacitor performs the feedback function for keeping the transistor active with a certain foxed frequency range.
The frequency of the circuit may be adjusted through the 4k7 pot and the 0.1uF capacitor so that any desired tone can be achieved at the output over the speaker.
The above adjustments helps to refine the tone of a particular bird to any form and helps to replicate the results as closely as possible.
220 V Bird sound Chirping Effect
The 220 V AC based "chirper" circuit sounds exactly like a bird. It offers a control which you can use to vary the tone of the fundamental sound output through lower frequencies to higher. When the speaker (4 to 6 inch should be adequate) is installed within the exact same box along with the circuitry, it can decide the complete scale the device.
Essentially the circuit is actually a free-running multivibrator. Pot R4 adjusts the frequency from around 1000 hertz to 10,000 hertz. The bird chirping effect is achieved by a low-frequency oscillator applying a neon bulb (M3).
This signal supplies base bias for transistor Q1. In case capacitor C1 is short circuited, the chirping effect is removed, and the circuit turns into a easy variable-frequency multivibrator. Transistor Q3 works like the driver stage, and Q4 is rigged as the output transistor.
T1 can be any standard audio output transformer as shown below: