DOD Phasor 595

Description: Protection against reverse voltage is implemented. A 10µF capacitor provides additional DC filtering. The CD4007 is configured as a flip-flop controlled by a foot switch. The output of the flip-flop drives the indicator. An 18V supply passes through a 100kΩ resistor to each of the non-inverting inputs and associated resistors of each operational amplifier, with the exception of the second LFO op-amp. The purpose of the two 100kΩ resistors is to provide a +9V bias point for the non-inverting inputs. Most operational amplifiers are designed to operate on a split power supply with equal single-ended power supply (+18V); thus, the op-amps must be biased to the midpoint of the supply voltage. This arrangement allows the op-amp to follow AC voltage swings on the input referenced to this bias point. The 100kΩ voltage divider is decoupled with a 10µF capacitor to ground (0V). If the op-amp's input were connected directly to this point, it would create a direct path to ground for AC signals, resulting in no sound. The non-inverting inputs are connected to this bias point through the 100kΩ resistors, isolating the AC signal from the AC ground and setting the input impedance of the circuit. There are some exceptions to this configuration, such as the second stage of the LFO, the output mixer amplifier, and the input buffer. The input buffer is biased through a 470kΩ resistor, maintaining an input impedance around 500kΩ to prevent loading of the input (guitar). The output mixer uses the inverting input to sum signals from the input buffer and the phase-delayed signal. The bias voltage can be applied directly to the non-inverting input without shunting the AC signals, resulting in an output that is 180 degrees out of phase with the input. Finally, the second LFO op-amp is biased from the output of the first stage. The DC voltage applied to the first stage non-inverting input appears at the output and, unless blocked by a capacitor, biases the next stage correctly.

The circuit described serves multiple functions, primarily focusing on audio signal processing and operational amplifier (op-amp) biasing. Protection against reverse voltage is critical in preventing damage to components, particularly in circuits that may experience incorrect polarity connections. The use of a 10µF capacitor for DC filtering is essential in smoothing out voltage fluctuations and ensuring stable operation of the op-amps.

The CD4007, functioning as a flip-flop, provides a digital control mechanism that can be activated via a foot switch, allowing for user interaction in audio applications, such as effects pedals. The output of this flip-flop is linked to an indicator, which could be an LED or other visual feedback mechanism, signaling the status of the circuit.

The biasing scheme involving two 100kΩ resistors is a classic approach in op-amp circuits, allowing the op-amps to operate effectively with AC signals by establishing a reference voltage at the non-inverting inputs. This is particularly important in audio applications where maintaining signal integrity is crucial. The decoupling capacitor ensures that AC signals do not short to ground, preserving the audio signal path.

The input buffer's design, with a higher impedance (around 500kΩ), is particularly advantageous when interfacing with high-impedance sources, such as electric guitars, as it minimizes loading effects that could distort the signal. The output mixer configuration, utilizing inverting inputs to sum various signals, is a common technique in audio processing, allowing for the blending of multiple audio sources while maintaining phase integrity.

The mention of the second LFO op-amp being biased from the output of the first stage indicates a cascading design, where the output characteristics of one stage directly influence the subsequent stage, enhancing the overall functionality of the circuit. This interconnected biasing is fundamental in ensuring that each stage of the circuit operates within optimal parameters, contributing to the desired audio effects.

Overall, this circuit exemplifies a well-thought-out design, integrating various electronic principles to achieve effective audio signal processing while maintaining the integrity and performance of the system.protection against reverse voltage. The 10mfd provides additional DC filtering. The CD4007 is configured as a flip-flop( )controlled by the foot switch. The output of the flip-flop drives the indicator The 18v appears to go through a 100k resistor, then to each of the non-inverting inputs and associated resistor of each opamp, with the exception o f the 2nd LFO opamp. Why of two 100k resistors. This provides a +9v bias point for the non-inverting inputs (+). Most opamps are designed to run on a split power supply with equal single ended power supply(+18v) you must bias the opamps to the middle of the supply voltage. This allows the opamp to follow AC voltage swings on the input referenced to this bias point. Notice that the 100k voltage divider is decoupled with a 10mfd cap to ground (0v). If the opamps input was connected directly to this point you would have an direct path to ground for AC signals (a short).

Therefore no sound! The non-inverting inputs are connected to this bias point through the 100k resistors. This isolates the ac signal from the AC ground and sets the input impedance of the circuit. Notice there are some exceptions to this, the second stage of the LFO, the output mixer amp and the input buffer. The input buffer is biased through a 470k resistor. This keeps the input impedance around 500k to prevent loading of the input (guitar). The output mixer is using the inverting input to sum the signals from the input buffer and the phase delayed signal.

The bias voltage can be input directly to the non-inverting input without shunting the AC signals. BTW this means this effect output is 180 degrees out of phase with the input. Finally the 2nd LFO opamp is biased from the output of the first stage. The DC voltage applied to the first stage non-inverting input appears at the output and unless blocked by a capacitor biases the next stage correctly. long answer to a short question!