Tremolo
circuit is a kind of sound effect. We can see this type of effect is
applied in guitar effect pedals. Tremolo effect is produced if we
modulate the amplitude of an audio signal. The shape of modulating signal can
vary from square wave, sawtooth wave, or sine wave. When we use a square wave,
then the effect produce a knocking-like sound which might be perceived like a
percussive instrument.
When
we use sine wave then we might perceive a kind of vibrato effect which gives
impression that there is a frequency modulation, but it is actually a psycho
effect because it modulate only the amplitude, not the frequency. This
tremolo circuit use very low frequency (VLF) as a source of modulating signal,
with frequency control by R12. The effect’s level, which is modulation depth,
is controlled by R11. The amplitude modulation is obtained by controlling the
gain of U1D, which has feedback path through Q1 which receives signal from U1C
phase oscillator. This is the figure of the schematic circuit diagram;
The power supply is rated
at 12V, but it actually works with 9V as well, so many standard audio effect
AD-DC adapter will do the job. If you want to build a custom power supply then
you can use small 15V 350 mA transformator with 7812 or 7809 integrated circuit
regulator series. The total current consumption should be lower than 10mA, so
you can even use smaller transformer like 21V 100mA, which is highly available
on the market because it is popular for TV booster application.
Be
careful in selecting the 78xx series regulator, because some manufacturers
specify different maximum input for this IC. A switch mode voltage regulator is
not really needed for this low power application, and it has worse noise figure
than the linear one. Some audio effect pedal has battery backup to guarantee
continues operation in case of power line failure, you can add 9V battery clip
to attach this backup supply, but don’t forget to provide power-on switch to
disconnect the battery when it’s not used. Finally, a power indicator LED is
very usable to provide power status indication.
