AR envelope generator

Description: This is a dual Attack/Release envelope generator that has been added to the Modular Benjolin design. While not essential, it provides enjoyable functionality, particularly when used alongside the modular rungle bit output mod. The circuit is straightforward, making it easy to build and use. Although a single envelope generator could suffice, the low component count and requirement for just one integrated circuit (IC) motivated the inclusion of two. Resistors R5 and R6 form a voltage divider that sets the threshold voltage at approximately 2.5 volts. Any incoming voltage exceeding this threshold will trigger the comparator, resulting in a high output of 9 volts for this circuit. The design employs a simple RC (resistor-capacitor) slope generator, with the attack and decay rates controlled by two potentiometers and capacitors (C1 for AR1 and C2 for AR2). Resistors R7 and R8 serve as peak limiters. The output from the operational amplifiers (pins 1 and 14) produces an envelope that oscillates between the power rails of +9VDC and -9VDC, typically swinging just below +9VDC and above -9VDC. For a bipolar envelope, the offset can be omitted. A trim potentiometer is installed to adjust the positive power supply, allowing for fine-tuning of the negative swing of the envelope to achieve a base voltage of exactly 0 volts. Although an oscilloscope is helpful for adjustments, it is not strictly necessary. An alternative testing method involves connecting the output of the AR generator to the control voltage (CV) input of a voltage-controlled oscillator (VCO), such as those in the Benjolin. To ensure the AR is not triggered, the connection to the VCO CV input should be unplugged and the pitch noted. After reconnecting, the offset potentiometer can be adjusted until the pitch remains consistent regardless of the connection.

This dual Attack/Release envelope generator circuit is designed for integration into modular synthesizer systems, exemplifying versatility and ease of use. The core functionality revolves around the generation of control voltage envelopes, which can modulate various parameters in synthesizers. The use of two envelope generators (AR1 and AR2) allows for complex modulation possibilities, enabling independent control over different aspects of sound synthesis.

The voltage divider formed by resistors R5 and R6 is crucial for establishing the trigger threshold, ensuring that only signals above 2.5 volts activate the envelope generators. This feature prevents unwanted triggering from noise or low-level signals, enhancing the reliability of the circuit in live performance or studio settings.

The RC slope generator's design allows for customizable attack and release times through the use of potentiometers. By adjusting these components, users can shape the dynamics of their sound, creating everything from sharp percussive hits to smooth, gradual swells. The choice of capacitors C1 and C2 will also influence the envelope response, with larger capacitance values resulting in slower envelope changes.

The peak limiting functionality provided by resistors R7 and R8 ensures that the output envelope does not exceed the desired voltage levels, protecting downstream circuitry from potential damage due to excessive voltage. This is particularly important in modular synthesizer environments, where multiple modules can interact and affect each other's performance.

The output envelope swings between the positive and negative power rails, allowing for both unipolar and bipolar envelope shapes based on user preference. The trim pot for offset adjustment is a valuable addition, enabling precise calibration of the envelope's baseline voltage. This feature is essential for achieving consistent performance across different setups and configurations.

In summary, this dual Attack/Release envelope generator circuit offers a simple yet effective solution for dynamic sound modulation in modular synthesizer systems. Its design emphasizes flexibility, ease of use, and adaptability, making it a valuable tool for both novice and experienced synthesists.By no means is this a necessary addition to the benjolin but its one I`ve had some fun playing with and decided to add to my Modular Benjolin design. This circuit is a dual Attack/Release envelope generator. The AR is especially useful when combined with the modular rungle bit output mod. This is a very simple design and is easy to build and use. It is also relatively easy to modify for other applications. You could definitely get by with one but its such a low part count and required just one IC so I decided to build two. R5 and R6 creates a voltage divider that sets your threshold voltage which has been set at around 2. 5volts. Any incoming voltage above 2. 5 volts will trigger the comparator and set the output high (which is 9 volts for this circuit). This is a simple RC (resistor capacitor) slope generator. The rate of attack and decay are determined by the two potentiometers and the capacitor (C1 for AR1 and C2 for AR2).

R7 and R8 act as peak limiters. The voltage coming out of the op amps (pin 1 and 14) is an envelope that swings between the power rails (+9VDC and -9VDC). In actuality it will swing just below +9VDC and above 9VDC. If you want a bipolar envelope then leave out the offset. I want the base voltage to be exactly 0 volts so I installed a trim pot to the positive power supply.

I use this to pull up the negative swing of the envelope until it is exactly 0 volts. It will take some fine adjustment. An oscilloscope will make it a lot easier but isn`t totally necessary. One way to test without a scope is to plug the output of the AR generator into the CV input of a VCO (like one of the ones on the benjolin). Make sure the AR is not being triggered. Unplug the connection to the VCO CV in and make a note of the pitch. Plug it back in and adjust the offset pot until the pitch is the same whether it is plugged in or not.