5
HOW THE QUAVERATO WORKS
The Quaverato is a very versatile tremolo pedal that produces all three types of tremolo sounds
mentioned above (bias, optical, and harmonic tremolo). When the guitar signal enters the pedal, it
is buffered with a low-gain amplifier stage and then immediately sent to the high pass and low pass
filters. The high pass filter (HPF) does exactly what it sounds like: it only lets high frequencies pass
through, and blocks the lower frequencies. The low pass filter (LPF) does just the opposite: it passes
low frequencies and blocks the high frequencies. See “Figure 2: Filters and Cutoff Frequency” on
page 6. The specific cutoff frequency for each of these filters is adjustable via an internal trimmer
potentiometer.
Next each signal is sent through a
unity gain amplifier and through
a digitally-controlled optocoupler.
Each optocoupler consists of a
light dependent resistor (LDR) and
a light emitting diode (LED). The
LDR is in series with the audio path.
When the LED is dark, the LDR’s
resistance is at maximum, which is
much too high for any audio signal
to get through. As the LED gets brighter, the LDR’s resistance lowers and allows signal to pass through.
At full brightness the LDR’s resistance is very low, allowing almost all of the signal to pass through.
The LED is digitally controlled by a microcontroller chip. This microcontroller produces an LFO which
causes the LED to turn on and off. The microcontroller has been programmed to give you a wide range
of control over how the LFO modulates the brightness of the LED.
Next the high and low frequencies are mixed back together. From there, the signal goes through a final
amplifier stage on its way to the volume control and finally the output jack.
For a complete discussion of the Quaverato’s features and controls, please see the Quaverato Owner’s
Manual, available from ww.zeppelindesignlabs.com.
Figure 1: Filter Crossover
Figure 2: Quaverato Block Diagram