This circuit already incorporates the amplification stage, since the oscillator is of the type of power, which can excite a heavy speaker with up to a few watts. The output transistor can be the TIP32 or BD136, which must be equipped with a heat radiator. Modulation is manual. By pressing the pressure switch S1, capacitor C1 charges slowly, thus polarizing the oscillator, which starts the operation with a low sound and becomes slightly higher. When the pressure switch is released, the capacitor charges and the sound changes smoothly from high to low until it stops. The circuit feedback capacitor C2 determines the average frequency of the sound, together with the charge and discharge resistors. Depending on the application, the resistors can be replaced by 100 k ohm trimpots in series with 10 k ohms resistors, and the capacitor can have values between 22 nF and 100 nF. In the same way, we can change the rise and fall time of the sound, that is, the modulation effect, with the use of electrolytic capacitors for C1 in the range of 22 u to 220 uF.
