DOD Phasor 595


Posted on Feb 7, 2014

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


DOD Phasor 595
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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...




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