Grind Customs DeProfundis Delay

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The DeProfundis Delay was designed by Grind Customs FX. It is a digital delay based around the commonly-used PT2399 delay chip, and in its stock form it offers a max delay up to roughly 600ms with minimal noise. The delay time is set by the resistance between pin 6 of the PT2399 chip and ground, which can be seen in the below schematic in Figure 4. Lower resistance means shorter delays, though if there is less than ~2k resistance to ground on power-up, the PT2399 will not function properly. The 2k2 resistor from pin 1 of the time pot to ground sets the minimum delay time and prevents this issue from occurring. There are workarounds to allow for shorter repeats out of a PT2399 without having issues with the PT2399 not functioning, but it requires additional parts. Extremely short delay times are more desirable for chorus and flanger effects, so the minimum resistance of 2k2 works well here. Conversely, increasing the resistance raises the delay time. Here, the max resistance from pin 6 to ground is 52k2 with the time pot turned all the way up. The max delay time of the DeProfundis Delay can be increased with more resistance, though at longer delay times the PT2399 can become quite noisy. If you would like to increase the max delay time, the next logical step up in potentiometer value is a 100K pot, however Grind Customs says that this circuit can handle about 75kΩ max from pin 6 to ground before the output becomes unusably noisy. In order to limit the potentiometer value and the series 2k2 resistor to ~75k, they recommend using a 100K Time potentiometer with a 270k resistor in parallel with lugs 1 and 2. This will result in a max delay time of roughly 900ms with a little more noise on the longest delay settings. For more info about how adjusting the potentiometer’s resistance works, see our “Potentiometers - Modifying Taper” tech article. There is a 10K tone trimpot on the board which is used to vary a high pass filter on the delayed signal. If desired, it can be replaced with a 10K linear potentiometer to make that an external control. See Figure 2 in our Guitar Pedal Footswitch and Jack Wiring article for the recommended footswitch and I/O wiring.