Tremolo

The voltage-controlled oscillator (VCO) of U1, part of a phase-locked loop, generates a low-frequency square-wave signal ranging from 5 Hz to 2500 Hz. The frequency is modulated by adjusting the voltage at pin 9 through resistor R2. The frequency threshold is established by resistor R1 and capacitor C1, where increasing the value of R1 raises the frequency, while decreasing the value of C1 lowers the threshold frequency. Transistor Q1 functions as an amplifier, with its quiescent point set at 4 V and utilizing a transistor with a voltage gain (beta) of 100. The gain without tremolo effect is approximately 2 V, whereas with bypass capacitor C4 included in the circuit, the gain is configured to 33 dB. The instrument drive must not exceed 30 mV when C4 is present (no tremolo) to prevent distortion. In contrast, without C4, the maximum allowable drive is 1.5 V without introducing distortion. The output of U1 is connected to the collector of transistor Q1 via depth control resistor R4. The square-wave signal modulates the audio at a frequency determined by R2. The oscillator is activated through foot switch S1.

The described circuit comprises several critical components that work together to produce a stable low-frequency square-wave signal. The VCO is central to the operation of the phase-locked loop (PLL), which ensures that the output frequency remains synchronized with a reference signal. The voltage at pin 9 of U1 is pivotal in controlling the frequency of oscillation; hence, the design of R2 is crucial for achieving the desired range of frequencies.

R1 and C1 form a timing network that sets the frequency threshold, and their values must be selected carefully to ensure that the VCO operates within the intended frequency range. The interaction between R1 and C1 allows for fine-tuning the frequency response, making it possible to achieve specific audio effects.

Transistor Q1 is employed as an amplifier to boost the square-wave signal generated by the VCO. Its quiescent point at 4 V is essential for linear operation, and the choice of a transistor with a high beta value ensures adequate amplification of the signal. The gain settings are adjustable, with a notable increase when the bypass capacitor C4 is included. This capacitor alters the gain characteristics, allowing for a higher output level while managing distortion.

The output coupling to the collector of Q1 via R4 enables modulation of the audio signal, which is influenced by the square-wave frequency set by R2. The depth control provided by R4 allows for further adjustment of the modulation effect, enhancing the versatility of the audio output.

The activation of the oscillator through foot switch S1 provides user control over the circuit's operation, making it suitable for live performance applications. The design ensures that the circuit remains robust against distortion, with specific thresholds established for both configurations with and without C4. This attention to detail in the circuit design contributes to a reliable and effective audio modulation system.The VCO of Ul, a phased-locked loop. produces a low-frequency square-wave signal from 5 Hz to 2500Hz, which is controlled by varying the voltage to pin 9 via R2. The frequency threshold is set by Rl and Cl. Increasing the value of Rl increases the frequency, and decreasing the value of Cl decreases the threshold frequency.

Transistor Ql is operated as an amplifier with the Q point at 4 V, using a transistor with a voltage gain (beta) of 100. The gain without tremolo is about 2 V. With bypass capacitor C4 in the circuit, the gain is set at 33 dB. The instrument drive cannot be greater than 30 mV with C4 in the circuit (no tremolo), to avoid distortion. Without C4, the drive can be 1.5 V maximum with no distortion. Ul"s output is coupled to the collector of transistor Ql via depth control R4. The square-wave signal pulls the audio at a frequency determined by R2. The oscillator is activated by foot switch Sl. 🔗 External reference